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![SPRINKLER IRRIGATION
101
10.6.2.2. Pressure and Topography
The topography in the field affects the pressure in the irrigation system. Elevation of 1
m. in topographic height decreases the pressure by 1 m. (0.1 atm.). Downward decline
of 1 m. increases the pressure by 1 m.
The slope along the pipe can be expressed in %. That facilitates the calculation of the
combined effect of friction in pipes and topography in each point in the field.
10.6.2.3. Nomograms and Slide-rulers
In daily use, the common practice of head-loss determination is accomplished by the
use of nomograms, slide-rulers and computers.
Fig. 10.5. Slide-ruler for Head-loss Calculation in Pipes
10.6.2.4. Head Losses in PVC and PE Pipes
The calculation of head losses in PVC and polyethylene pipes is similar to that of
aluminum pipes. Since the plastic pipes are designated by their nominal external
diameter, it is necessary to know the wall thickness. Knowing the external diameter
and wall thickness facilitates the calculation of the internal diameter and the net cross-
section of the pipes. These values are required for the calculation of head losses
according to the Hazen-Williams formula and for the use of the common head-loss
nomograms, in which the internal diameter is the related parameter.
As mentioned before, in plastic pipes, as the nominal working pressure is higher, the
wall thickness has to be greater and hence the internal diameter and the free cross-
section will be smaller.
For example, in PE pipes of 50 m m . of 4, 6 and 8 bars. working pressure classes,
the greatest internal diameter is in the grade 4 pipe and the smallest is in the grade 8
pipe. For the same flow-rate, the higher head-losses will occur in the 8-grade pipe and
the lower in the 4-grade pipe. Two distinct nomograms are given on page 104 for the
most prevalent PE pipe diameters of rigid (high density) and soft (low-density) PE
pipes.
Calculation example: (using the Hazen-Williams nomogram)
The head -loss of a 3" aluminum sprinkler lateral with 16 sprinklers, positioned 12 m apart,
has to be calculated. The nominal (average) sprinkler flow-rate (discharge) is 1.5 m3
/h; the
length of the lateral is 186 m. The friction coefficient [C] of the pipeline is 120.](https://image.slidesharecdn.com/sprinklerirrigationtechnologyandapplicationshandbook-2011-complete-140819035034-phpapp02/85/Sprinkler-Irrigation-Technology-and-Applications-2011-122-320.jpg)
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SPRINKLER IRRIGATION
than 0.15 is poor. With the recent improvements in manufacturing tolerances, most
emitters have Cvm < 0.10.
The manufacturing flow-rate variation is determined statistically. Samples of emitters
are selected randomly and tested under constant pressure.
11.5.2.2. Emission Uniformity (EU), combines variation due to emitter manufacturer
variance and variation due to pressure. This is a design parameter. In new
installations or when emitter clogging is not occurring, EU (design) is approximately
equal to DU.
EU is given as:
EU = [(1 -1.27(Cvm)) X (Qn/Qavg) X 100] (Eq. 11.11)
Where,
Cvm = manufacturer’s coefficient of variation,
Qmin = minimum emitter discharge due to reduced pressure,
Qavg = mean emitter discharge due to pressure.](https://image.slidesharecdn.com/sprinklerirrigationtechnologyandapplicationshandbook-2011-complete-140819035034-phpapp02/85/Sprinkler-Irrigation-Technology-and-Applications-2011-151-320.jpg)
![SPRINKLER IRRIGATION
194
13.2.2. Climate Data
a. Rainfall – amount and seasonal distribution.
b. Reference Evapo-transpiration (ET0) – calculated from climatic variables
(Penman-Monteith method) or measured in Class A pan.
12.2.3. Cropping Data
a. Growth season
b. Phenological stages – dates, time-length, foliage coverage, root-zone depth,
sensitivity to water stress.
c. In-row and between row spacing.
d. Peak season crop coefficient (kc): the ratio between ETc (crop water loss by
evapo-transpiration) and the ET0.
The crop coefficient kc has been elaborated for use in fully wetted soil surface
technologies like overlapping sprinkler irrigation. For partial soil surface wetting
technologies, the ETc may be adjusted downwards. The component of evaporation
from soil surface is significantly reduced in partial wetting pattern, due to the small
percentage of wetted soil surface.
The adjustment can be made using the equation:
ETca = ETc × [0.1(GC)0.5
] (Eq. 13.1)
Where:
ETca = Adjusted ETc
GC = Percentage of ground cover, The percentage of ground cover relates to the
shaded soil surface by the crop foliage at midday.
13.2.4. Water resources
The second set of data is the water source and the water quality.
13.2.4.1. Water Supply Capacity
The parametrs needed for system design:
a. Water source characteristics (river, dam, pond, well, public/commercial supply).
b. Hours of supply (if by external supplier or due to restrictions on electricity supply)
c. Maximum available hourly/daily flow-rate (discharge).
d. Pump pressure-discharge curve (if applicable).
e. Pressure at supply connection (if by external supplier).
f. Water quality (physical contamination, hardness, salinity).
If a public or commercial supplier provides the water, the head, maximum available
flow-rate at the supply points and supply hours have to be validated.
Additional data have to be gathered about the crop water requirements, the climate
conditions, the amount and the season of rainfall and the sensitivity of the crop to
the irrigation-dependent environment factors like salinity and the wetting of the
foliage.
With the above-mentioned data at hand, the selection of the irrigation method and
emitter can be considered.
The parameters to be considered are the application-rate that has to correspond to
the water intake-rate of the soil, the duration of the application that has to
correspond with the wind conditions, water quality and crop sensitivity to foliage](https://image.slidesharecdn.com/sprinklerirrigationtechnologyandapplicationshandbook-2011-complete-140819035034-phpapp02/85/Sprinkler-Irrigation-Technology-and-Applications-2011-215-320.jpg)
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SPRINKLER IRRIGATION
retained in the soil after irrigation or rain, when the rate of downward movement has
substantially decreased, usually one to three days after irrigation or rain ended.
Filter area - The total area of a filtration element, usually expressed in square
centimeters or square inches.
Filter cake - The debris accumulated on the filter element, blocking it, resist the
water flow through the filter and increase the differential pressure.
Filter - A device which removes particles from water by means of a physical barrier,
chemical process and/or biological process.
Filtration degree - Size of pores in filtration medium (expressed in mm, micron or
mesh units).
Filtration element - The active component of the filter, it determines the type of filter
and the filtration level.
Filtration velocity - Flow-rate per cross section area [m/hr].
Filtration - The process of removing solid particles from fluid by forcing them through
a porous medium.
Flange - A flat metal ring with a hole in its center, through which a pipe passes, and
with a number of smaller holes drilled circumferentially, destined for the connecting
bolts.
Float valve - A valve which automatically opens or closes as the level of a liquid
changes. The valve is operated mechanically by a float which rests on the top
surface of the liquid.
Flood - An overflow of water onto lands that are used or usable but are not covered
normally by water. Floods have two essential characteristics: The inundation of land
is temporary; and the land is adjacent to and inundated by overflow from a river,
stream, lake, or ocean.
Flood Irrigation - A method of irrigating with water that is applied from field ditches
onto land that has no guide preparation such as furrows, borders or corrugations.
Flow - The movement of fluids, through pipe, fittings, nozzles, valves or other
vessels. Measured in Cubic Meters Per Hour (m3/h), Liters Per Minute (l/m), Liters
Per Second (l/s), Gallons Per Minute (GPM), Gallons Per Hour (GPH), Cubic Feet
Per Second (ft3
/s).
Flowing well/spring - a well or spring that taps ground water under pressure so that
water rises without pumping. If the water rises above the surface, it is known as a
flowing well.
Flow-rate - The amount of water moving through an emitter, a pipe, fixture, stream,
etc. Volume of water per unit of time, measured in l/h or m3
/h.
Flush-flow - High initial momentary flow through an irrigation lateral; required to flush
the lateral and emitters before the working pressure is built-up.
Freshwater - Water that contains less than 1,000 milligrams per liter (mg/l) of
dissolved solids. More than 500 mg/L of dissolved solids is undesirable for drinking
and many industrial uses.
Friction-loss - The pressure lost as water flows through pipes, fittings and valves of
an irrigation system. As the velocity of water flowing through the system increases,](https://image.slidesharecdn.com/sprinklerirrigationtechnologyandapplicationshandbook-2011-complete-140819035034-phpapp02/85/Sprinkler-Irrigation-Technology-and-Applications-2011-261-320.jpg)
![246
SPRINKLER IRRIGATION
returned to the source.
Non-Point Source (NPS) pollution - Pollution discharged over a wide land area, not
from one specific location. These are forms of diffuse pollution caused by sediment,
nutrients, organic and toxic substances originating from land-use activities, which are
carried to lakes and streams by surface runoff. Non-point source pollution is
contamination that occurs when rainwater, snowmelt, or irrigation washes off plowed
fields, city streets, or suburban backyards. As this runoff moves across the land
surface, it picks up soil particles and pollutants, such as nutrients and pesticides.
Non-volatile memory - A feature in irrigation controllers that will retain the
programmed information in electronic memory during a power failure, without the
need for a battery.
Normally Closed (NC) valve - An automatic valve through which no water will flow
unless external actuation is applied that trigger the valve to open. Most electric
valves are of the normally closed type.
Normally Open (NO) valve - An automatic valve through which water will flow
unless external actuation is applied to close the valve. Most hydraulic valves are of
the normally open type.
Nozzle - The final orifice through which water is emmited from the emitter to the
atmosphere.
Open area - The Pore Area of the filter medium; expressed often as a percentage of
its total area.
Operating pressure - The pressure at which a device or irrigation system is
designed to operate.
Organic Matter (OM) - Plant and animal residues, or substances generated by living
organisms. All are based upon carbon compounds.
Orifice - Discharge hole in an emitter or lateral.
Osmosis - The movement of water molecules through a thin membrane. The
osmosis process is one method of desalinating saline water.
Outfall - The place where a sewer, drain, or stream discharges; the outlet or
structure through which reclaimed water or treated effluent is finally discharged to a
receiving water body.
Oxygen demand - The need for molecular oxygen to meet the needs of biological
and chemical processes in water. Even though very little oxygen is dissolved in
water, it is extremely important in biological and chemical processes.
Ozonation - The process of applying ozone (O3
) to a liquid for disinfection purpose.
Pan evaporation - Evaporative water losses from a standardized pan used to
estimate crop evapo-transpiration and assist in irrigation scheduling.
Particle size - The diameter, in millimeters, of suspended sediment or bed material.
Particle-size classification is:
[1] Clay—0.00024-0.004 millimeters (mm);
[2] Silt—0.004-0.062 mm;
[3] Sand—0.062-2.0 mm;
[4] Gravel—2.0-64.0 mm.](https://image.slidesharecdn.com/sprinklerirrigationtechnologyandapplicationshandbook-2011-complete-140819035034-phpapp02/85/Sprinkler-Irrigation-Technology-and-Applications-2011-267-320.jpg)
![254
SPRINKLER IRRIGATION
chemical-physical methods. Activated sludge and trickling filters are two of the most
common methods of secondary treatment. It is accomplished by bringing together
waste, bacteria, and oxygen. This treatment removes floating and suspended solids
and about 90% of the oxygen-demanding substances and solids. Disinfection is the
final stage of the secondary treatment.
Sediment - A material in suspension in water or recently deposited from suspension.
In the plural the word is applied to all kinds of deposits from the waters of streams,
lakes, or seas.
Sediment load - Amount of sediment carried by running water.
Sedimentation - Deposition of waterborne sediments due to a decrease in velocity
and corresponding reduction in the size and amount of sediment which can be
carried in the water.
Sedimentation tanks – (1) Wastewater tanks in which floating wastes are skimmed
off and settled solids are removed for disposal. (2) Tank for sedimentation of sand
and other solids from the water by extremely slowing water movement by flowing
through very wide cross-section.
Seepage - (1) The slow movement of water through small cracks, pores, Interstices,
etc., of a material into or out of a body of surface or subsurface water. (2) The loss of
water by infiltration into the soil from a canal, ditches, laterals, watercourse, reservoir,
storage facilities, other bodies of water, or from a field.
Self-supplied water - water withdrawn from a surface or groundwater source by a
user rather than being obtained from a public supply.
Semi-arid climate - A climate characterized by 250 – 500 mm of annual
precipitation.
Sewage treatment plant - A facility designed to receive the wastewater from
domestic and/or industrial sources and to remove materials that downgrade water
quality and threaten public health and safety when used for irrigation or discharged
into receiving streams or bodies of water. The substances removed are classified into
five basic groups:
[1] greases and fats;
[2] solids from human waste and other sources;
[3] dissolved pollutants from human waste and decomposition products;
[4] dangerous microorganisms;
[5] poisonous industrial residues.
Most facilities employ a combination of mechanical removal steps and bacterial
decomposition to achieve the desired results. Chlorine is often added to the water to
reduce the danger of spreading diseases by the release of pathogenic bacteria.
Sewer - A system of underground pipes that collect and deliver wastewater to
treatment facilities or streams.
Simple water budget - A water budget that is the product of reference evapo-
transpiration, irrigated area, and a conversion factor, relating to the specific
requirements of the crop.
Sludge - The residual semi-solid material left from the water reclamation process.
Snaking - Laying of loosened laterals to allow temperature induced contraction and](https://image.slidesharecdn.com/sprinklerirrigationtechnologyandapplicationshandbook-2011-complete-140819035034-phpapp02/85/Sprinkler-Irrigation-Technology-and-Applications-2011-275-320.jpg)
Uploaded byAyman Morshedy
Sprinkler Irrigation Technology and Applications, 2011
This document provides an overview of sprinkler irrigation technology and applications. It discusses various types of sprinkler systems including conventional sprinkler irrigation, micro-irrigation, and mechanized irrigation. It also covers topics such as pumping units, pipes and accessories, regulation and control components, water treatment and filtration, fertigation, flow rates, water movement in soil, sprinkler irrigation techniques, planning and design, irrigation scheduling, monitoring and control, and maintenance. The document is intended to serve as a textbook on sprinkler irrigation systems for farmers, extension workers, and policy makers.
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Sprinkler Irrigation Technology and Applications, 2011
- 1. SPRINKLER IRRIGATION TECHNOLOGY ANDAPPLICATION Moshe Sne Irrigation and Plant Nutrition Consultant 2011
- 2. I FOREWORD Ten years agoI had composed in cooperation with the late Elimelech Sapir the booklet “Sprinkler Irrigation”. The publication was used as a textbook in courses on irrigation organized by the Israeli Ministry of Foreign Affairs, The Centre for International Cooperation (Mashav), through its agricultural aegis The Centre for International Agricultural Development Cooperation (CINADCO), of the Israeli Ministry of Agriculture and Rural Development. The courses were carried-out in Israel and abroad for farmers, extension workers and policy makers in the field of irrigation and water management. They were designated for beginners and first time users of pressurized irrigation. Elucidation of the theoretical concepts was simplified to correspond with course participants' requirements. In the last decade, irrigation technologies became more advanced and more sophisicated, perceptions and attitudes were changed, so updating this publication had been essential. The booklet covers the technology and theory of sprinkler irrigation. In addition to conventional sprinkler irrigation, two derivative technologies are dealt – micro-irrigation and mechanized irrigation. Micro-irrigation employs micro emitters of low volume water discharge with two patterns of water distribution: a. Water is distributed through the air. b. Water is delivered directly to the soil from drippers and bubblers. The booklet relates only to those emitters that spread the water through the air, drippers and bubblers are excluded. The mechanized irrigation stemmed from sprinkler irrigation. In its first generation, the emitters were solely impact sprinklers. Later-on it shifted to using micro-emitters operating at low working pressure. This technology is gaining momentum all over the world. For that reason it is covered with much more detail than in the first edition. The manuscript emphasizes the practical aspects of sprinkler irrigation. The more advanced reader may refer to the extensive literature dealing with the subject. Related publications are listed in the References and Bibliography list at the end of the booklet. I have chosen to distribute the new publication by the Scribd network with the hope that users of the old version can update themselves. Moshe Sne
- 3. II TABLE OF CONTENTS TOPICPage Forword I Table of Contents II List of Tables IX List of Figures XI 1. INTRODUCTION 1 Overview …………………………………………………………………. 1 Surface Irrigation ………………………………………………………… 2 Surface Irrigation Methods …………………………………………….. 2 Advanced Technologies ………………………………………………... 3 2. SPRINKLER IRRIGATION 4 Introduction ………………………………………………………………. 4 Advantages ……………………………………………………………….. 4 Disadvantages and Limitations …………………………………………... 4 Definitions ………………………………………………………………... 5 Nominal Pipe Diameter ………………………………………………… 6 Sprinkler Types …………………………………………………………... 6 Sprinkler Classification ………………………………………………… 7 The Jet Angle …………………………………………………………... 13 Sprinkler Flow-rate …………………………………………………….. 14 Working Pressure (Head) ………………………………………………. 14 Sprinkler Spacing, Selection and Operation …………………………... 14 3. MICRO-EMITTERS 16 Introduction ………………………………………………………………. 16 Micro-emitter types ………………………………………………………. 17 Static Micro-emitters (Micro-jets) ……………………………………... 17 Micro-sprinklers ………………………………………………………... 18 Micro-sprinkler Types …………………………………………………. 19 Emitter Mounting ………………………………………………………… 20 Water Distribution Patterns ………………………………………………. 21 Pressure Compensation …………………………………………………... 22
- 4. III 4. THE IRRIGATIONSYSTEM 23 The Pumping Unit ………………………………………………………... 23 Pump Performance Terminology ………………………………………. 24 Pump Types …………………………………………………………….. 25 Suction Lift of a Pipe …………………………………………………... 26 Kinetic Pumps ………………………………………………………….. 27 Installation of Vertical Turbine Pumps ………………………………… 31 Submersible Pumps …………………………………………………….. 31 Pump Stages ……………………………………………………………. 32 Solar water Pumps and Solar Water Pumping Systems ………………... 33 Variable speed drives …………………………………………………... 33 Selecting an Efficient Pumping Plant ………………………………….. 34 Maintaining Irrigation System Efficiency ……………………………… 34 The Pumping Unit Efficiency ………………………………………….. 35 Cavitation ………………………………………………………………. 37 Pump Curves …………………………………………………………… 37 Pump and Well Testing ………………………………………………… 39 5. PIPES AND ACCESSORIES 40 Introduction ………………………………………………………………. 40 Pipe Materials …………………………………………………………….. 40 Iron, Steel and Copper ………………………………………………….. 40 Aluminum ………………………………………………………………. 41 Asbestos-cement ………………………………………………………... 41 Concrete ………………………………………………………………... 41 Plastic Materials ………………………………………………………... 41 External and Internal Pipe Diameter ……………………………………... 45 6. COUPLERS 46 Connectors (Fittings) ……………………………………………………... 46 Aluminum Couplers ……………………………………………………. 46 7. REGULATION AND CONTROL 49 Introduction ………………………………………………………………. 49 Supply Pipelines ………………………………………………………… 49
- 5. IV The Control head…………………………………………………………. 49 Regulation and Control Devices …………………………………………. 50 Valves ………………………………………………………………….. 50 Control Valves – Functioning and Actuation ………………………….. 55 Check-valves …………………………………………………………… 58 Pressure Relief Valves …………………………………………………. 59 Pressure Regulators …………………………………………………….. 60 Air-release Valves ……………………………………………………… 61 Atmospheric Vacuum Breakers ………………………………………... 62 Valve Capacity …………………………………………………………… 62 Automation ……………………………………………………………….. 62 Overview ……………………………………………………………….. 62 Flow-meters …………………………………………………………….. 63 Metering-valves (Hydrometers) ………………………………………... 64 Control Patterns ………………………………………………………… 64 Irrigation Timers ……………………………………………………….. 65 Computer-based Irrigation control Systems ……………………………. 66 Supervisory Control And Data Acquisition (SCADA) ……………….. 68 8. WATER TREATMENT AND FILTRATION 71 Introduction ………………………………………………………………. 71 Particulate Matter ………………………………………………………… 71 Biological Substances ……………………………………………………. 71 Chemical Precipitates …………………………………………………….. 72 Water hardness …………………………………………………………… 72 Iron and Manganese in Water ………………………………………….. 73 Biological Oxidation Demand (BOD)…………………………………….. 73 Filtration ………………………………………………………………….. 73 Screen (Strainer) Filters ………………………………………………... 73 Disc Filters ……………………………………………………………... 75 Media Filters …………………………………………………………… 75 Sand Seperators ………………………………………………………… 76 Filter Characteristics …………………………………………………… 77
- 6. V Flow Direction ………………………………………………………….78 Filter Cleaning …………………………………………………………. 79 Filter Location ………………………………………………………….. 81 Supplementary Water Treatments ………………………………………... 81 Chlorination …………………………………………………………….. 82 Acidification ……………………………………………………………. 82 9. FERTIGATION 83 Introduction ………………………………………………………………. 83 Advantages of fertigation ………………………………………………. 83 Limitations and Risks in Fertigation …………………………………… 83 Technologies of Fertigation ……………………………………………… 83 Patterns of Injection ……………………………………………………. 83 Fertilizer Tank ………………………………………………………….. 84 Venturi Injector ………………………………………………………… 85 Injection pumps ………………………………………………………… 85 Injecton Site ……………………………………………………………… 88 Injection at the Main Control Head …………………………………….. 88 Injection at Sub-main Heads …………………………………………… 88 Injection at the Control Head of each Block …………………………… 88 Control and Automation ………………………………………………….. 88 Quantitative Dosing ……………………………………………………. 88 Proprtional Dosing ……………………………………………………... 88 Avoiding Corrosion damage ……………………………………………... 89 Back-flow Prevention …………………………………………………….. 89 Back-siphonage ………………………………………………………… 89 Back-pressure …………………………………………………………... 89 Chemical Aspects of fertigation ………………………………………….. 89 Safety ……………………………………………………………………... 90 10. FLOW-RATE – WATER HEAD RELATIONSHIP 91 Water Pressure ……………………………………………………………. 91 Elevation Head (z) ……………………………………………………… 91 Dynemic head ….. ………..……………………………………………. 92
- 7. VI Velocity Head …………………………………………………………...92 Head Losses ……………………………………………………………… 92 Friction Losses …………………………………………………………. 92 Operating Pressure ……………………………………………………….. 96 Hydraulic Characteristics of Emitters ……………………………………. 97 Calculation of Head Losses ………………………………………………. 98 Technical data ……………………………………………………………. 98 Pressure measurement ………………………………………………….. 98 Calculation of Longitudinal Head Losses ……………………………… 98 11. WATER MOVEMENT AND DISTRIBUTION IN THE SOIL 109 Soil Properties ……………………………………………………………. 109 Soil Texture …………………………………………………………….. 109 Soil – Water relationship …………………………………………………. 111 Introduction …………………………………………………………….. 111 Saturation ………………………………………………………………. 111 Field Capacity 111 Wilting Point …………………………………………………………… 111 Factors affecting the Difference in Water Storage ……………………... 111 Available Water Capacity (AWC) ……………………………………... 112 Water Movement in the Soil …………………………………………… 112 The Determination of the Water Status in the Soil …………………….. 114 Water Intake Rate (WIR) of the Soil …………………………………… 115 Soil Wetting Patterns ……………………………………………………... 120 Water dosage …………………………………………………………… 120 Chemical Composition of the Water …………………………………… 120 Water Distribution Uniformity …………………………………………… 120 Distribution Uniformity in Fully Soil Surface Wetting Irrigation ……... 121 Distribution Uniformity in Localized irrigation ……………………….. 129 12. SPRINKLER IRRIGATION TECHNIQUES 131 Overview …………………………………………………………………. 131 Hand-move ……………………………………………………………….. 131 Aluminum Pipes ………………………………………………………... 131
- 8. VII Flexible laterals inOrchards …………………………………………… 133 Permanent Installations …………………………………………………... 134 Solid-set in Orchards …………………………………………………… 134 Mini-sprinklers Solid-set Systems in Vegetables ……………………… 135 Mechanized Irrigation ……………………………………………………. 137 Introduction …………………………………………………………….. 137 Towline ………………………………………………………………… 137 Wheel Move ……………………………………………………………. 138 Traveling Gun (Traveler) ………………………………………………. 141 Continuous-move Sprinkler System ……………………………………… 147 The Water Emitters …………………………………………………….. 147 Center-Pivots …………………………………………………………… 157 Lineat-Move Systems …………………………………………………... 182 Control and Automation ………………………………………………... 187 13. PLANNING AND DESIGN OF SPRINKLER IRRIGATION 192 Introduction ………………………………………………………………. 192 Planning …………………………………………………………………... 192 Soil Properties ………………………………………………………….. 192 Climate Data ……………………………………………………………. 194 Cropping Data ………………………………………………………….. 194 Water Resources ………………………………………………………... 194 Data Manipulation ………………………………………………………... 195 Soil Wetting Pattern ……………………………………………………. 195 Manipulation Steps ……………………………………………………... 196 Existing Equipment ………………………………………………………. 198 Calculation Formulae …………………………………………………….. 200 The Design Procedure ……………………………………………………. 201 Overview ……………………………………………………………….. 201 System Layout ………………………………………………………….. 201 Water Flow Velocity …………………………………………………… 203 Spacing …………………………………………………………………. 203 Choosing Emitters and Laterals ………………………………………... 204
- 9. VIII Fxample of theDesign Process …………………………………………... 204 Additional Examples of System Design Schemes ……………………….. 209 14. IRRIGATION SCHEDULING 212 Introduction ………………………………………………………………. 212 Calculation of the Water Amount in Sprinkler Irrigation ………………... 213 Calculation of the Precipitation Rate …………………………………... 213 Calculation of the Irrigation Duration ………………………………….. 213 The Total Flow-rate of the Irrigated Area ……………………………… 213 Scheduling with the water Budget Concept ……………………………. 214 Scheduling Software and On-line Calculators …………………………. 216 15. MONITORING AND CONTROL 219 Monitoring ………………………………………………………………... 219 Soil Water Monitoring …………………………………………………. 219 Plant Water Status Monitoring …………………………………………. 220 Plant Organs Elongation and Expansion ……………………………….. 221 Irrigation Control ………………………………………………………… 221 Manual Control ………………………………………………………… 221 Quantitative Automatic Water Shutdown ……………………………… 221 Fully Controlled Irrigation ……………………………………………... 221 Integrated Irrigation and Fertigation Control …………………………... 221 Integrated monitoring and Control ……………………………………... 222 16. MAINTENANCE 223 Introduction ………………………………………………………………. 223 Installation ………………………………………………………………... 223 Mains and Sub-mains …………………………………………………... 223 Laterals …………………………………………………………………. 223 Routine Inspection ……………………………………………………….. 224 Pump Inspection ………………………………………………………... 224 System Performance ……………………………………………………. 224 Routine Maintenance ……………………………………………………... 225 System Flushing and Cleaning …………………………………………. 225 The Control Head ………………………………………………………. 225
- 10. IX The Irrigation Network…………………………………………………. 226 Micro-irrigation Systems ………………………………………………. 228 Mintenance of Accessories ……………………………………………... 228 Maintenance of Fertigation Systems …………………………………… 230 Chemical Water Treatments ……………………………………………… 230 Acidification ……………………………………………………………. 230 Oxidation ……………………………………………………………….. 231 Overwintering of the Irrigation System ………………………………….. 231 Entire System …………………………………………………………... 231 Filtration Equipment …………………………………………………… 231 Valves …………………………………………………………………... 231 Controllers and Sensors ………………………………………………… 231 Chemical Injection Equipment …………………………………………. 231 Pumps …………………………………………………………………... 232 Electric Motors …………………………………………………………. 232 17. GLOSSARY 233 18. REFERENCES AND BIBLIOGRAPHY 262 LIST OF TABLES No. PAGE 2.1. Wind Velocity Definitions ……………………………………………. 15 2.2. Recommended Spacing between Sprimklers …………………………. 15 5.1. PE (Polyethylene) Pipes for Agriculture ……………………………... 42 5.2. LDPE Pipes Internal (Inner) Diameter and Wall Thickness …………. 43 5.3. HDPE HDPE Pipes Internal (Inner) Diameter and Wall Thickness …………. 43 5.4. PVC Pipes for Agriculture ……………………………………………. 44 5.5. Internal Diameter and Wall Thickness of PVC Pipes ………………… 44 7.1. Flow-rate of Spring Actuated Pressure Regulators …………………… 61 8.1. Relative Clogging Potential of Micro-emitters by Water Contaminants 72 8.2. Screen Perforation Examples …………………………………………. 74 8.3. Sand Particle Size and Mesh Equivalent ……………………………... 76
- 11. X 8.4. Nominal FilterCapacity – examples ………………………………… 78 9.1. Electric Charges of Nutrients ………………………………………… 90 10.1. Pressure and Water Potential Units …………………………………... 91 10.2. Friction Coefficients ………………………………………………… 93 10.3. Multiple Outlets factor F ……………………………………………… 97 10.4. Effect of the Emitter Exponent on Pressure – Flow-rate Relationship . 97 10.5. Head Losses in Non-Distributing Aluminum Pipes, m. Head per 100- m. Pipe Length (without Outlets) …………………………………….. 99 10.6. F Coefficient in Laterals ……………………………………………… 100 11.1. Soil Classification According to Particle Diameter …………………... 109 11.2. Available Water in Different Soil Textures ………………………….. 112 11.3. Average values of Water States in Different Soil Textures – W/W …. 112 11.4. Calculating Christiansen's Coefficient of Uniformity with Experimental Data (example) ………………………………………………………… 127 12.1. Recommended Hose Size for Traveler Sprinklers …………………… 147 12.2. Characteristics and Performance of the Emitters …………………….. 165 12.3. Wetting Diameter of Emitters at 1.8 m3 /h Flow-rate ………………… 171 12.4. Recommended Spacing – m. for Emitters at 2 m. Height at Different Working Pressures ……………………………………………………. 177 13.1. Sprinkler Performance (example) ……………………………………. 199 13.2. Maximum Allowed Number of Sprinklers on Lateral on Level Ground 201 13.3. The Chosen Emitter …………………………………………………... 206 13.4. Allowed Length of Laterals …………………………………………... 206 13.5. Basic data …………………………………………………………….. 207 13.6. Head-loss Calculation ………………………………………………… 208 13.7. Total Requested Dynamic Head ……………………………………… 208 14.1. Annual Crops Irrigation Scheduling Form …………………………… 212 14.2. The Estimated Available Water per Unit of Rooting Depth for Soils of Various Textures and the Intake Rate for Various Soil Textures ……. 214 14.3. Active Root-zone Depth of Fruit Trees ………………………………. 215
- 12. XI LIST OF FIGURES No.PAGE 1.1. Level Border Strip Flooding ………………………………………… 2 1.2. Leveled Beds between Contour Lines ……………………………….. 3 1.3. Furrow Irrigation …………………………………………………….. 3 2.1. Sprinkler Spacing Positions …………………………………………. 5 2.2. Irrigation Intensity …………………………………………………… 5 2.3. The Influence of Wind on the Uniformity of Water Distribution …… 6 2.4. Outdated Pressurized Irrigation Systems ……………………….. 6 2.5. Impact-Hammer Sprinkler …………………………………………… 8 2.6. Turbo-Hammer Sprinkler ……………………………………………. 8 2.7. Gun Sprinkler (Rain-gun) ……………………………………………. 8 2.8. Stand-alone Gun-sprinkler with Stabilizer in the Field ……………… 9 2.9. Pop-up Sprinklers ……………………………………………………. 10 2.10. Part-circle Static Sprinklers ………………………………………….. 10 2.11. Impact Sprinkler Components …………………………………… 11 2.12. Configurations of Impact Sprinklers ………………………………… 12 2.13. Nozzle Types ………………………………………………………… 13 2.14. Jet Angles ……………………………………………………………. 13 2.15. Low-volume Under-canopy Sprinklers ……………………………… 14 3.1. Diverse Micro-emitters …………………………………………….. 16 3.2. Static Micro-jets ……………………………………………………... 17 3.3. Vortex Sprayer ………………………………………………………. 18 3.4. Vibrating Micro-jet ………………………………………………….. 18 3.5. Modular Micro-emitter – Water Spreading Pattern …………………. 18 3.6. Rotating Micro-sprinklers …………………………………………… 19 3.7. Micro-sprinklers Configurations …………………………………….. 19 3.8. Modular Micro-sprinkler …………………………………………….. 19
- 13. XII 3.9. Mounting Alternativesof Micro-emitters …………………………... 21 3.10. Water Distribution by Micro-sprinkler at Different Flow-rates ……... (example) 22 3.11. Multiple-jet (Fan-jet) Emitter's Distribution Patterns ……………….. 22 4.1. Schematic Plot Irrigation System ……………………………………. 23 4.2. Electric Water Pumps ……………………………………………… 23 4.3. Pump Type Classification …………………………………………… 25 4.4. Centrifugal Pump ……………………………………………………. 27 4.5. Different Flow Patterns in Centrifugal Pumps ………………………. 28 4.6. Water Flow in Volute Pump ………………………………………… 29 4.7. Deep-well Verical Turbine Pumps …………………………………... 30 4.8. Pump Impellers ……………………………………………………… 31 4.9. Single-stage Pump …………………………………………………… 32 4.10. Multi-stage Pump ……………………………………………………. 32 4.11. Solar Pumping System ………………………………………………. 33 4.12. A Variable-frequency Drive Controlls a Set of 3 Pumps …………... 33 4.13. Pump Efficiency Curve ……………………………………………… 36 4.14. A Scheme of Pump Curves ………………………………………….. 37 4.15. An Example of Pump Curves Plotted on One sheet …………………. 38 4.16. Horse-power Curves …………………………………………………. 38 4.17. Critical Points on the Pump Curve …………………………………... 39 6.1. Hermetic and Detached Band Couplers …………………………….. 46 6.2. Single Latch Couplers ………………………………………………. 46 6.3. Valve Adapters ………………………………………………………. 47 6.4. Adapter Made of Al-Pb Metal Alloy ………………………………... 47 6.5. Aluminum Lateral Assembly ………………………………………... 47 6.6. Plastic and Metal Connectors ………………………………………... 47 6.7. Lock Fastened PolyPropylene Connectors ……………………………….. 48 6.8. On-line Saddles ……………………………………………………… 48 7.1. Water Supply Network .…………………………………………… 49
- 14. XIII 7.2. Typical ControlHead ..…………………………………………….. 49 7.3. Valve Types …………………………………………………………. 50 7.4. Manual Actuators ……………………………………………………. 50 7.5. Globe Valve …………………………………………………………. 51 7.6. Angular Valve ……………………………………………………….. 51 7.7. Single-seat Globe Valve ……………………………………………... 52 7.8. Double-seat Globe Valve ……………………………………………. 52 7.9. Gate Valve …………………………………………………………… 53 7.10. Ball Valve Cutaway …………………………………………………. 53 7.11. Butterfly Valve ………………………………………………………. 54 7.12. Piston Valve …………………………………………………………. 54 7.13. Diaphragm Valve Components ……………………………………… 55 7.14. Diaphragm Valves …………………………………………………… 55 7.15. Diaphragm Valve Working Pattern ………………………………….. 55 7.16. Control Valve Actuators ………………………………….………… 56 7.17. Cutaway of Solenoid Valve …………………………….…………… 56 7.18. Scheme of Solenoid Operation ……………………………………… 57 7.19. Fail Closed (NC) Solenoid Valve – Components and Working Pattern ……………………………………………………………….. 57 7.20. Hydraulic Control Valve …………………………………………….. 58 7.21. Check Valves ………………………………………………………… 59 7.22. Pilot Controlled Hydraulic Pressure Relief Valves ………………….. 59 7.23. Pilot Valves ………………………………………………………….. 60 7.24. Pressure Regulators ………………………………………………….. 60 7.25. Cross Section of Air-release Valves ……………………………… 61 7.26. Atmospheric Vacuum Breakers ……………………………………... 62 7.27. Flow-meters …………………………………………………………. 63 7.28. Hydrometers – Cross-section ………………………………………... 64 7.29. Hydrometer – Manual and Remote-controlled Dial ………………... 64
- 15. XIV 7.30. Local IrrigationController …………………………………….. 67 7.31. SCADA Control System ……………………………………………. 68 7.32. RTUs Connected to Field-unit (FU) by Cable ………………………. 69 7.33. Internet Mediated SCADA Network ………………………………… 70 8.1. Screen Filter …………………………………………………………. 73 8.2. Screen Patterns ………………………………………………………. 74 8.3. Head Losses in Clean Screen Filters ………………………………… 75 8.4. Disc Filter ……………………………………………………………. 75 8.5. Media Filters ………………………………………………………… 76 8.6. Sand Separator - Working Pattern …………………………………… 76 8.7. Hydro-cyclone Sand Separator – Head Losses and Optimal Flow- rates ………………………………………………………………….. 77 8.8. Manual Cleaning of Screen filters …………………………………… 79 8.9. Hose Flushing of a Disc-filter ……………………………………….. 79 8.10. Continuous Flushed Circulating-filter ………………………………. 79 8.11. Automatic Screen Filters with Scanning Nozzles …………………… 80 8.12. Automatic Flushing of Disc-filter …………………………………… 80 8.13. High-capacity Media-filter Array ……………………………………. 81 8.14. Back-flushing of Media-filters ………………………………………. 81 9.1. Fertilizer Tank ……………………………………………………….. 84 9.2. Venturi Injector ……………………………………………………… 85 9.3. By-pass Venturi Installation …………………………………………. 85 9.4. Piston and Diaphragm Hydraulic Pumps ……………………………. 86 9.5. No-drain Hydraulic Pump …………………………………………… 86 9.6. Piston Pump Installation in Control Head …………………………… 87 9.7. Fertilizer Solution Flow-meter with Pulse Transmitter ……………………. 87 9.8. Mixer Array ………………………………………………………….. 87 9.9. Electric Pump ………………………………………………………... 88 9.10. Tandem Back-flow Preventer ………………………………………... 89
- 16. XV 10.1. Graphic Presentationof Friction Head ……………………………….. 94 10.2. Feeding Micro-tube Connection ……………………………………... 95 10.3. Head-losses in Hydraulic Valves ……………………………………. 95 10.4. Pressure Measurement ……………………………………………... 98 10.5. Slide-ruler for Head-loss Calculation in Pipes ………………………. 101 10.6. Nomogram for Hazen-Williams Formula ………………………….. 103 10.7. Nomograms for Head-loss Determination In Polyethylene Pipes ………. 104 10.8. Nomogram for Local Hydraulic Gradient Determination in Accessories …………………………………………………………… 105 10.9. Nomogram for Calculation of Head-losses in LDPE Pipes …………. 106 .10.10 Nomogram for Calculation of Head-losses in HDPE Pipes …………. 107 10.11. Nomogram for Calculation of Head-losses in PVC Pipes …………... 108 11.1. Visual Illustration of Soil Particle Diameter ………………………… 109 11.2. Soil Texture Triangle ………………………………………………... ………………………………………………… 110 11.3. Illustration of the Water States in the Soil …………………………... ..11111111111111111111111 111 11.4. Water-air Ratio in Two Soil Types, 12 Hours After Irrigation ……… 111 11.5. Illustration of the Available Water in the Soil ………………………. 112 11.6. Water Potential Values in the Different Water States in the Soil …… 113 11.7. Water Retention Curves in Different Soil Textures …………………. 114 .11.8 The Sequence of Soil Moisture Determination by the Gravimetric (Oven Drying) Method ………………………………………………. 115 11.9. Edelman Dutch Auger ……………………………………………….. 11.10. Water Infiltration into the Soil – Curve ……………………………... 115 11.11. Soil Texture Triangle – Infiltration Rate Contours ………………….. 116 11.12. Typical Infiltration Curves in Different Soil Textures ………………. 116 11.13. The Basin Infiltrometer ……………………………………………… 117 11.14. Double Ring Infiltrometer …………………………………………… 118 11.15. The “Sprinkler Method” ……………………………………………... 119 11.16. Single Sprinkler Test ………………………………………………… 122
- 17. XVI 11.17. Single LateralTest …………………………………………………... 123 11.18. Simultaneously Operated Laterals Test ……………………………… 123 11.19. Open-air Test Plot and Covered Distribution Test Facility …………. 123 11.20. Grid of Catch Cans …………………………………………………... 124 11.21. Recording Form for Measurement of the Uniformity of Water Distribution ………………………………………………………….. 125 11.22. Measured Water Amounts in One Quarter of the Wetted Area in Single-sprinkler Test …………………………………………………. 126 11.23. Single Sprinkler Distribution Pattern in Wind-less Conditions ……... 126 11.24. Wind Effect on the Distribution Pattern on Both Sides of a Single Lateral ………………………………………………………………... 128 11.25. Unilateral Presentation of the Distribution Pattern of a Mini-emitter …. 128 12.1. Hand-move Lateral ………………………………………………….. 131 12.2. Hand-move Layout: 2” Aluminum Pipes, Spacing 6 X 12 m. 4 Laterals X 4 Positions………………………………………………… …………………………………………………………. 132 12.3. Coupling of Aluminum Pipe …………………………………………. 132 12.4. Ten-shift Manual Drag Under-canopy Sprinkler Array ……………. 133 12.5. Orchard Under-canopy Micro-sprinkler Irrigation ……………… ……….………………. 134 12.6. Solid-set System in Orchard. Spacing 6 X 4 m. Sprinkler Flow-rate … 100 l/h 134 12.7. Orchard Overhead Irrigation ………………………………………… 135 12.8. Solid-set Mini-sprinkler Irrigation of Vegetables …………………… 136 12.9. Towline ……………………………………………………………... 137 12.10. Towline Accessories …………………………………………………. 137 12.11. Linear Towline System: 2 Sets, 8 Laterals Each, Six Positions per Lateral, Spacing 12X18 m ………………………………………….. 138 12.12. Sprinkler Vertically Stabilized by a Swivel and a Ballast …………... 139 12.13. Side-roll Operating Scheme …………………………………………. 140 12.14. Side-roll in the Field …………………………………………………. 140 12.15. Manually Moved Big Gun ………………………………………. 142 12.16. Hose-reel Traveler …………………………………………………… 143
- 18. XVII 12.17. Cable-tow Traveler………………………………………………….. 143 12.18. Hose-reel Traveler Operating Scheme ………………………….. 144 12.19. Water-driven Cable-tow Traveler Scheme ………………………….. 145 12.20. Cable-tow Traveler Operating Scheme ……………………………… 145 12.21. Linear-Move System with On-top High-pressure Impact Sprinklers and End-gun …………………………………………………………. 148 12.22. Impact Sprinkler – Nozzle Options ………………………………….. 148 12.23. Stationary Deflection-pad Emitters ………………………………….. 150 12.24. Nozzle and Deflection-pad Options for Stationary Spray …………… 150 12.25. Micro-emitters On-drops in Work ……………………………………………….. 151 12.26. Nozzle and Pad Options in Rotators …..…………………………….. 151 12.27. Up-right Spinner ……………..…….………………………………… 151 12.28. Rotators and Spinner ………………………………………………… 152 12.29. Distinctive Emitters ………………………………………………….. 152 12.30. LDN Emitters at Work ………………………………………………. 153 12.31. LDN (Low Drift Nozzle) Emitter Configurations …………………… 154 12.32. Oscillating Deflection Pad Options ………………………………….. 155 12.33. Components of Oscillating Emitters ………………………………… 155 12.34. Inverted Wobbler on Drops ………………………………………….. 155 12.35. Diverse Configurations of Inverted Wobblers ……………………… 156 12.36. Quad-spray and its Water Application Modes ……………………… 156 12.37. Aerial View of Center-Pivot Irrigated Area …………………………. 157 12.38. Center-Pivot Operation Scheme ……………………………………... 157 12.39. Net Irrigated Area …………………………………………………… 157 12.40. Components of Center-Pivot / Linear-Move Lateral System ……….. 158 12.41. Universal System (Can Be Used as Linear-Move or Center-Pivot) …. 159 12.42. Center-Pivot Main Tower …………………………………………. 160 12.43. Corner Arm ………………………………………………………….. 160 12.44. Options of Sprinkler Position and Dicharge ………………………… 161
- 19. XVIII 12.45. Towable Center-Pivot……………………………………………….. 163 12.46. Goosenecks on Top of lateral ………………………………………... 166 12.47. Positioning Options of Low-pressure Emitters on Drops …………… 167 12.48. Furrow Dikes ………………………………………………………… 168 12.49. Boom-backs behind Center-Pivot Towers …………………………... 169 12.50. Bi-lateral Boom Appendage with end-gun on a Center-Pivot ………. 170 12.51. Emitter Spacing Patterns in Center-Pivot ……………………….. 173 12.52. An Example of Water Logging by Spray Emitters - Close-up ……… 174 12.53. The Effect of Using Pressure Regulators in Slopy Terrain …………. 174 12.54. Small-diameter Pressure Regulators Installed for Single Emitters ..… .and on Drops 175 12.55. Relationship between Width of the Wetted Coverage (W) and Application Intensity for the Same Flow-rate ……………………….. 176 12.56. Relationship between Required Application Intensity and Time of Application for the Same Depth of Application …………………….. 177 12.57. Center-Pivot End-gun Installations ………………………………….. 178 12.58. Irrigation of Orchards by Center-Pivot ………………………………. 179 12.59. Linear-Move Lateral ………………………………………………… 182 12.60. On-lateral Trip Switch ………………………………………………. 183 12.61. Linear-Move System with Spray Emitters on Drops ………………... 184 12.62. Linear-Move System with Rotators on Drops ………………………. 185 12.63. Linear-Move – Main-line in Field Margin …………………............... 186 12.64. Linear-Move System Pumping Water from Ditch …………………... 186 12.65. Operation Scemes of Ditch-fed Linear-Move Systems ……………… 186 12.66. VRI with Individual Emitter Control ………………………………... 188 12.67. VRI – Partially Irrigating Lateral ……………………………………. 189 12.68. Individually Controlled Node ……………………………………….. 189 12.69. Control Panel Positioned in the Pivot point …………………………. 189 12.70. On-screen Operation Presentation …………………………………... 191 13.1. Topographic Map ……………………………………………………. 192
- 20. XIX 13.2. Irrigation PlanningForm …………………………………………….. 193 13.3. Different Design Alternatives ……………………………………….. 202 13.4. Manifolds Save in Cost of Accessories ……………………………… 202 13.5. Citrus Grove - 11.5 Ha. ……………………………………………… 204 13.6. The Design Sceme …………………………………………………… 207 13.7. Hand-move Design Scheme …………………………………………. 209 13.8. Gun Traveler Design Scheme ……………………………………….. 210 13.9. Solid-set in Orchard …………………………………………………. 211 14.1. Typical Root Systems of Field Crops ……………………………….. 215 14.2. Irrigation Design Software Screenshot ……………….……………... 216 14.3. Visual Presention of Designed System ……………………………… 217 14.4. Scheduling Software Screen-shot …………………………………… 217 14.5. On-line Calculator …………………………………………………… 218 15.1. Tensiometers ………………………………………………………… 219 15.2. Watermark Granular Sensor …………………………………………. 219 15.3. Time Domain Transmissometry Sensor ……………………………... 219 15.4. The Pressure Bomb ………………………………………………….. 220 15.5. Fertilizer and Water Controller ……………………………………… 221 15.6. Integrated Monitoring and Control ………………………………….. 222 16.1. Punch and Holder ……………………………………………………. 223 16.2. Automatic Lateral End Flushing Valve ……………………………… 225 16.3. Control Head ………………………………………………………… 225 16.4. Coupling of PE Pipes ……………………………………………….. 226 16.5. Replacing Seal ………………………………………………………. 226 16.6. Insertion of Emitters In Small-diameter Soft PE Lateral ….………. 227 16.7. Components of Hydraulic and Metering Valves. The Wear- sensitive Components ……………………………………………… 227 16.8. Sprinkler Tools ……………………………………………………… 227 16.9. Sprinkler components ………………………………………………. 227
- 21. XX 16.10. Micro-jets andMini-sprinklers Components ……………………….. 228 16.11. Vertical Stake ………………………………………………………... 229 16.12. Flow Regulator ……………………………………………………… 229
- 22. SPRINKLER IRRIGATION 1 1. INTRODUCTION 1.1Overview Water scarcity, soaring energy costs, deterioration of agricultural land and desertification, threaten agricultural development and food production for the fast growing world population. Irrigated agriculture increases twice to ten-fold the yield per land unit, compared with non-irrigated farming. Irrigation has its roots in the history of mankind and is even mentioned in the Bible: “A stream flows from Eden to irrigate the garden...” (Genesis, 10). The prosperous ancient civilizations developed fresh water sources and delivery systems that were used for irrigation. In years of drought, people were forced to migrate in search of water. Unfortunately, innumerable wars were triggered by water scarcity. Rivers and streams are natural water conveyors. Natural and artificial lakes are used as water reservoirs. The construction of dams converts segments of rivers' courses into reservoirs and increases their water storage capacity. Following the introduction of pumps, pipelines were installed as water conduits. The pipes are made of steel, aluminum, concrete and plastic materials. Population growth triggered long distance conveyance of water and promoted the development of water engineering and the derived science of hydraulics. Irrigation can be regarded as the science of survival. Gigantic irrigation water supply projects were built throughout the ancient world. Among them: The 1,200 km long Grand Canal in China. Water supply and irrigation systems were constructed thousands of years ago in India and Sri Lanka. Today, engineers are still impressed by the sophistication of ancient water delivery systems and the irrigation techniques employed. The Romans constructed sophisticated aqueducts, dozens of km long to deliver water to the new built cities. In Egypt, food production is fully dependent on the Aswan dam that stores water for irrigation of the Nile valley and some of the adjoining desert and guarantees food supply to the population. Prior to the harnessing of electricity, water had to be conveyed by gravity, along natural slopes that required the construction of canal networks, for the water flow and excavating the water path accordingly. This practice had its limitation, since water could not be conveyed to the lands lying above the water sources. A remarkable revolution in irrigation technology commenced with the development of pumps that enabled lifting water above the height of the water source. Irrigation technologies are classified into two main categories: a. Surface (non-pressurized) irrigation - furrow, borders, flooding, basins, etc. b. Pressurized irrigation - sprinkler, spray and drip irrigation (including mechanized irrigation). Surface irrigation is regarded as the most wasteful irrigation technology. Irrigation efficiency is mostly below 40%. In sprinkler and mechanized irrigation, the efficiency ranges from 60% to 85%. In micro-irrigation, the efficiency can attain 90% - 95%. Salinization of irrigated lands is the most prevalent trigger of desertification (conversion of cultivated land to desert). More than one million hectares of arable land on the globe is lost annually due to salinization.
- 23. SPRINKLER IRRIGATION 2 Careful waterapplication in optimal timing and dosage with timely salt leaching when needed, is a prerequisite for long-run sustainable agriculture and inhibition of salinization. Sprinkler irrigation, facilitates the elimination of salinization by leaching the accumulating salts out of the active root-zone by precise application of the required water amount. There are significant differences between surface and sprinkler irrigation in the pattern of water movement and distribution in the soil. Ponding of water on the soil surface, in furrows and small basins is common in surface irrigation while water ponding in sprinkler irrigation indicates the existence of non-permeable soil layers or exessive water application rate, above the percolation capacity of the soil. In today's raised standards of living, more attention is given to irrigation of residential and recreational facilities like home gardens, lawns, sports and golf courses. The equipment used is partially adapted from agricultural appliances and partially dedicated gear that is designed specifically for these facilities. 1.2. Surface Irrigation Surface irrigation is the most widespread irrigation technique used on the globe. More than 90% of the 280 million irrigated hectares in the world are irrigated by surface irrigation. Surface irrigation methods can be classified into a number of techniques. The selection of the method depends on factors such as cropping technology, climate, soil type, topography, water availability and distribution facilities, farmers mentality and tradition. The most significant soil factors are the structure and the physical properties of the soil: soil texture, soil permeability; water flow on the soil surface and its movement in the soil; field capacity and wilting point; soil aeration. The most relevant climate factors are precipitation and evaporation rates during the growing season. Thorough consideration of the above-mentioned factors and incorporation of advanced techniques as zero slope leveling, SCADA (Supervisory Control And Data Acquisition) and surge (intermittent, pulsating application of water flow) irrigation, may facilitate achieving, by this “ancient technology”, efficient water use, high yields and good produce quality. 1.2.1. Surface Irrigation Methods Fig. 1.1. Level Border Strip Flooding 1.2.1.1. Level Border Strip Flooding The level border bed (broad-bed, or paddy) resembles a broad furrow (4 - 18 m wide), bordered by levees, with zero slope across its width and a longitudinal slope not greater than 1%. By opening the floodgate at the head of the bed, or by activating siphons, the bed is filled with water from a ditch or a furrow. This method, which is fit
- 24. SPRINKLER IRRIGATION 3 for appropriatelyleveled topographic structures only, requires some land leveling and a high water flow-rate. Wetting the bed during a short period of time prevents water losses beneath the root zone depth. The performance of the system should be examined by field tests (advance and retreat of water as a function of time). Rice, banana, alfalfa and other field crops are usually irrigated by this method. 1.2.1.2. Leveled Beds between Contour Lines This method is similar to border strip flooding, however the bed walls are contour lines as shown in the illustration to the right. 1.2.1.3. Furrows The water is distributed in the field by means of narrow ditches, each of them delivering water to one or two rows of plants. Obtaining good irrigation efficiency necessitates two stages of watering. In the first stage a high flow-rate is sent to wet promptly the soil surface along the entire furrow. Then a second lower flow-rate is delivered in a longer time period. 1.2.2. Advanced Technologies Zero slope leveling and surge irrigation are two procedures that increase irrigation efficiency in surface irrigation. These procedures can be applied with both flood and furrow irrigation. 1.2.2.1. Dead Level Layout When high precision land leveling, supported by laser sensors is applied, zero slope, dead level layout can be practical. Irrigation efficiency in this layout can be much higher than in the traditional layouts. Width of area between borders is limited to 100 – 150 m. 1.2.2.2 Surge Irrigation The principle of surge irrigation is the splitting of water application to several pulses. The first pulse is of high volume of water. It is aimed to wet as fast as possible the entire length of the irrigated bed or furrow without inducing erosion. That first flow partially seals the upper layer of the soil and enables the next pulses to be of smaller volumes for longer time periods, rendering even depth percolation along the flow path. Modern surge irrigation layouts employ automatic surge valves that direct water in alternating pulses to different sectors of the plot according to pre-planned timetable. Fig. 1.2. Leveled Beds between Contour Lines Fig. 1.3. Furrow Irrigation
- 25. SPRINKLER IRRIGATION 4 2. SPRINKLERIRRIGATION 2.1. Introduction Sprinklers were first introduced at the beginning of the twentieth century as pressurized irrigation emitters for the irrigation of flower gardens. Later-on they were adapted to the irrigation of field crops, plantations and greenhouses. Sprinkler irrigation was extensively expanded after the Second World War when aluminum became a cheap and widely available commodity and flat land, suitable for non-pressurized irrigation became scarce. Sprinkler irrigation enables simultaneous operation of many laterals of sprinklers, facilitates accurate water measurement and regulation of the water application rate to the water intake rate of the soil. 2.2. Advantages a. Sprinkler irrigation is suitable to diverse topographic conditions like uneven lands and steep slopes that cannot be irrigated by surface irrigation. b. A vast selection of emitters and nozzles facilitates the matching of the water application rate to the intake rate of the soil. c. Uniform distribution of water in the field renders high water use efficiency. d. Easy and simple operation, only short training of the operators is required. e. Capability of accurate measurement of the applied water amount. f. Prospective high mobility of the irrigation equipment from one field to another. g. The operation of solid-set and mechaniized systems, minimizes labor requirement. h. Feasibility of frequent - small water dosage applications for germination, cooling, frost protection, etc. i. The closed water delivery system prevents contamination of the flowing water, decreasing the occurrence of emitter clogging. j. Convenient blending of fertilizers with the irrigation water. k. Handy integration with automation and computerized irrigation control devices. 2.3. Disadvantages and Limitations a. High initial investment. b. Extra cost of the energy consumed for creation of water pressure. c. Sensitivity to wind conditions. d. Water losses by evaporation from soil surface, the atmosphere and plant canopy. e. Induction of leaf-diseases in overhead irrigation. f. Hazard of salt burns on wetted foliage in overhead irrigation. g. Washout of pesticides from the foliage in overhead irrigation. h. Interference of irrigation with diverse farm activities like tillage, spraying, harvesting, etc. i. Hazard of soil surface encrustation and enhancement of runoff from soil surface. j. Water losses in plot margins.
- 26. SPRINKLER IRRIGATION 5 2.4. Definitions 2.4.1.Pressure: a force acting on an area, expressed in units of kg/cm2 , bars, atmospheres or PSI (Pounds per Square Inch). 2.4.2. Water head: the pressure at the base of a water column, expressed in meter units. The head in the bottom of a water column 10 m. high, is 10 m. = 1 bar. ≈ 1 atm. 2.4.3. Water amount: measured in volume units. In the metric system the common units are liter (l) and cubic meter (m3 ) (1,000 l = 1 m3 ). 2.4.4. Water flow-rate (discharge): the amount of water flowing through a certain cross-section per time unit. In the metric system the units are: m3 /h or liter/h (l/h). 2.4.5. Wetting diameter: the diameter of a circle of soil surface, wetted by a certain sprinkler = twice the wetting radius of the sprinkler. Measured in meters. 2.4.6. Sprinkler spacing: the spacing between the sprinklers along and between the sprinkler laterals. For example: 12 m x 18 m. a. Rectangular Position b. Diagonal Position Fig. 2.1. Sprinkler Spacing Positions 2.4.7. Irrigation Intensity: the force of the water drops exerted on the soil surface during precipitation. The intensity depends on the number of drops, their size, their velocity and the impact angle at which they hit the soil surface. The intensity is expressed in qualitative terms: high, medium, low. a. High Intensity – Rough Droplets b. Low Intensity – Fine Droplets Fig. 2.2. Irrigation Intensity
- 27. SPRINKLER IRRIGATION 6 2.4.8. Application(precipitation) rate: the amount of water applied to an area unit per a unit of time: 1 mm/h = 1 m3 per 0.1 Ha/h = 10 m3 per Ha per hour. 2.4.8. Irrigation interval: The time interval between two water applications = the period between the start of one irrigation cycle and the start of the following one. 2.4.9. Irrigation cycle: The period between the beginning and the termination of one irrigation event of a certain area. 2.4.10. Wind velocity: expressed in meters per second (m/sec.) or km/h units. Fig. 2.3. The Influence of Wind on the Uniformity of Water Distribution 2.4.11. Nominal pipe diameter: The nominal diameter of steel and asbestos- cement pipes, up to 10" is the internal diameter, measured in inches (1 inch = 25.4 mm.) In wider diameters, as well as in aluminum, plastic pipes and tubes the nominal diameter is the external diameter, measured in inches in aluminum pipes and in mm. in pipes made of plastic materials. 2.5. Sprinkler Types In the early years, water under pressure had been applied by nozzles mounted along oscillating galvanized cast iron pipes. The oscillating movement was driven by the inherent water pressure in the irrigation system. Another means for water distribution was perforated tin pipes laid on the soil surface. a. Skinner Oscillating Pipe System b. Perforated Pipe (Perf-O-Rain) Fig. 2.4. Outdated Pressurized Irrigation Systems After Benami & Ofen 1993 Contemporary sprinklers are made of metal and plastic materials. The sprinklers are mounted on metallic or plastic risers of various heights, corresponding to the irrigation technique and the crop canopy height.
- 28. SPRINKLER IRRIGATION 7 2.5.1. SprinklerClassification Sprinklers are classified according to their function, pattern of operation, working pressure, flow-rate, materials from whom they are made, etc. 2.5.1.1. Sprinkler Function Sprinkler function classification is based on the crop and growing technologies, for whom the sprinkler type is designated. 2.5.1.1.1. General use: Impact sprinklers with jet angle of 300 , one or two nozzles, are used for overhead irrigation in field crops, forage and vegetables, as well as in overhead irrigation in orchards, in hand move, solid-set and towed laterals. 2.5.1.1.2. Under-canopy sprinklers: used for irrigation in orchards. The jet angle is 40 - 70 . This group is comprised of under-canopy impact-hammers, turbo-hammers, whirling sprinklers, mini-sprinklers, microsprinklers and microjets – rotors, spinners, sprayers and ray-jets (multiple jets). These emitters are used also for solid-set irrigation in vegetables and flowers in the open field and greenhouses and in mechanized irrigation. 2.5.1.1.3. Gun sprinklers: Used for irrigation of wide-scale field crops and forage areas, may be used as stand-alone units, in laterals, moved by hand or installed on self-propelled travelers and in center pivots and lateral move machines, as end- guns. 2.5.1.1.4. Part circle sprinklers: These sprinklers are installed at lateral ends, plot margins and in specific situations in mechanized laterals in order to avoid water losses beyond plot borders and wetting of roads and sidewalks. 2.5.1.1.5. Regulated sprinklers: May be pressure-compensated or flow-regulated. Simplifies design and operation in harsh topography conditions. 2.5.1.1.6. Pop-up sprinklers: Used in irrigation of lawns, golf courses and residential areas. 2.5.1.1.7. Small-size impact and turbo-sprinklers: are used for under canopy irrigation in orchards, and overhead irrigation in open field and protected vegetables and flowers. 2.5.1.1.8. Static sprinklers are used in small residental gardens. 2.5.1.2. Pattern of Operation Sprinklers are operated by water pressure. A water jet that is ejected from a nozzle activates the moveable component of the sprinkler. 2.5.1.2.1. Rotating impact sprinkler: The water jet, emitted from the nozzle, hits the hammer arm, pushing it in counter-clockwise direction. A spring returns the arm back. Its strike on the sprinkler body results in rotary movement of the body in the opposite direction. The impact sprinklers are fitted with one, two or three nozzles. This sprinkler type is manufactured in diverse configurations. With a 300 ejection angle it is used for overhead irrigation of field crops and orchards. For under-canopy irrigation of orchards the recommended jet angles are 40 -70 . Initially. the sprinklers were made of metal, but later-on, plastic materials were also used. The wear of moving parts and nozzles made of reinforced plastic, is much lower than that of metallic ones. Although impact sprinklers are highly reliable, they require strict routine maintenance to guarantee consistent operation along time. 2.5.1.2.2. Turbo-hammer sprinkler: The water jet stirs a grooved wheel that hits the
- 29. SPRINKLER IRRIGATION 8 hammer. Theimpact of the hammer rotates the sprinkler. The turbo-hammer sprinklers are made of plastic material and are used for the irrigation of orchards, vegetables and gardens at low flow-rates. Fig. 2.5. Impact-Hammer Sprinkler Fig. 2.6. Turbo-Hammer Sprinkler From "Naan" Brochure 2.5.1.2.3. Gun Sprinklers Fig. 2.7. Gun Sprinkler (Rain-gun) Big size hammer sprinklers are made of brass with two or three nozzles. The working pressure is high (4 - 8 bars). The sprinkler flow-rate range is 6 - 60 m3 /h. Gun
- 30. SPRINKLER IRRIGATION 9 sprinklers areused for irrigation of forage and field crops in solid-set schemes, in Center-Pivot and Lateral-Move irrigation machines and as a traveling gun in "stand- alone" configuration. Fig. 2.8. Stand-alone Gun-sprinkler with Stabilizer in the Field 2.5.1.2.4. Pop-up sprinklers - commonly used for lawn and golf courses irrigation. The sprinkler pops upwards at the beginning of the irrigation and falls back after shut- down into its underground housing, where it remains in stand-by position until the next irrigation. In the underground stand-by position it allows the undisturbed use of lawns, parks or golf courses, and does not interfere with lawn mowers' operation. There is a wide-range of pop-up sprinkler types, including part-circle sprinklers, as well as rise-ups of various heights. 2.5.1.2.5. Gear-driven sprinklers are used mostly in residential and public lawns irrigation. Some gun sprinklers are also driven by a turbine and velocity reduction gear. 2.5.1.2.6. Rotor and rotary stream sprinklers often incorporate a small water turbine which, by means of reducing gears, provides for slow, continuous nozzle or nozzle head rotation. Gear-drive mechanisms require clean water to prevent clogging and wear.
- 31. SPRINKLER IRRIGATION 10 a. Gear-drivenb. Part-circle Impact c. Pop-up Sprinkler Irrigating A Lawn Fig. 2.9. Pop-up Sprinklers 2.5.1.2.7. Static sprinklers – are made of brass or rigid plastic materials, without moving parts. These sprinklers are used mainly in residential gardens. They irrigate a full or partial circle. The wetting range is smaller as compared to rotating sprinklers. Manufacturers' catalogs provide the essential data about the specifications and performance of the sprinklers. Information is given about flow-rate (Q), and the effective wetting diameter (D), in the range of the allowed working pressure (P). Additional data relate to the recommended spacing between sprinklers, the precipitation rate and distribution uniformity. a. Fixed Angle b. Adjustable Angle Fig. 2.10. Part-circle Static Sprinklers
- 32. SPRINKLER IRRIGATION 11 2.5.2. Componentsof Impact Sprinklers 2.5.2.1. Base: It is the connection to the riser. It has internal or external thread, manufactured in diameters of 0.5” - 3". 2.5.2.2. Tube: It is inserted in the base and fixed to the body of the sprinkler. Between the base and the tube there are located 1 - 3 seals that function as bearings to smooth the rotation of the sprinkler and minimize wear from the friction of the tube with the base. 2.5.2.3. Sand protection mechanism: Consists of a thrust spring and an external plastic sleeve that prevents the intrusion of sand and grit from the outside. 2.5.2.4. Body: Accommodates the housings in which the nozzles are fitted and carries the moving parts of the sprinkler. The body can be of one of the configurations: 2.5.2.4.1 Bridge: In some sprinkler types, the hammer is connected to the body by means of a shaft fixed to a bridge between two vertical supports. The sprinkler rotation is activated by the impact of the hammer on one of the supports. The reverting spring surrounds the shaft. 2.5.2.4.2. Crown: Other types of sprinklers are bridge-less. The spring is connected above the hammer by a plastic or metallic crown. Under frost or dusty conditions, an external plastic cover protects the spring. 2.5.2.5. Spring: Stimulates the rotation of the sprinkler by returning the hammer arm that was activated by the water jet that was emitted from the nozzle. In the Bridge Sprinkler, the spring is fixed within a fastening frame while in the Crown Sprinkler the spring is not fixed within the frame. In a Crown Sprinkler, the spring tension can be adjusted to the size of the nozzle and the water head. Springs are commonly made of copper, however when using reclaimed water, stainless steel springs are recommended. 2.5.2.6. Hammer arm: Activates the sprinkler rotation. Wetting range and distribution are determined by the number of strikes per minutes (30-60). There are two types of hammer arms: 2.5.2.6.1. Spoon drive: a rigid arm without moving parts, used in medium and high pressure conditions. 2.5.2.6.2. Wedge (dual action) drive: a plastic wedge is fitted on a shaft at the edge of Fig. 2.11. Impact Sprinkler Components
- 33. SPRINKLER IRRIGATION 12 the arm.Used in low-pressure conditions prone to malfunction for small diameter wetting. 2.5.2.7. Buffer: Absorbs partially the energy of the hammer impact to Minimize the wear of the body by the strikes and acts as a guide to the arm. a. Spoon Drive b. Wedge (Dual Action) Drive c. Part-circle Sprinkler d. Bridge Sprinkler e. Crown Sprinkler f. Protected Crown Sprinkler Fig. 2.12. Configurations of Impact Sprinklers 2.5.2.8. Nozzles Each sprinkler is fitted with one, two or three nozzles. The nozzle type and size determine the flow-rate, the distribution pattern and uniformity and the droplets size. Nozzles are prone to wear and change of the flow-rate as well as the water distribution pattern. Irrigation water containing sand is abrasive and may expand the nozzle aperture and increase the flow-rate, as well as change the distribution pattern. Plastic nozzles are more resistant to abrasion than metallic ones. There are different types of nozzles. A circular cross-section of the nozzle's aperture, indicates a long range jet while an elliptic or half-crescent cross-section indicates a short-range wetting diameter. Maximum range is achieved by a jet angle of 300 related to the soil surface while in under-canopy sprinklers, 40 and 70 angles are dominant. Nozzle size is expressed as its diameter in mm. Since the nozzle cross- section is not always circular, size definition may be quoted as the nominal size that is equivalent to a nozzle of circular cross-section with an identical flow-rate. Ordinarily, the nozzle size is stamped on the nozzles. In plastic nozzles it is common
- 34. SPRINKLER IRRIGATION 13 to distinguishbetween different sizes by different colors. Fig. 2.13. Nozzle Types After S. Elhanani, 1961 The nozzle flow-rate (Q) depends on the water pressure head, the diameter of the nozzle's aperture and its friction coefficient. (Eq. 2.1) Where: Q = Nozzle flow-rate (discharge), expressed as liters per hour (l/h) P = Water pressure head, expressed in m (meters) D = Nozzle nominal diameter, expressed in mm C = Friction coefficient. Its value for small nozzles, up to 5.5 mm. = 0.95. For medium size nozzles, 5.5-8 mm. = 0.9 For large nozzles, over 8 mm. = 0.85. The pressure dependent flow-rate for a certain nozzle is: (Eq. 2.2) Where: Q1 = The flow-rate at the P1 head. Q2 = The flow-rate at the P2 head. 2.5.3. The Jet Angle The angle of the water stream ejected from the nozzle determines the range, the sensitivity to wind and the water distribution pattern. Larger angles, up to 450 , render longer range but higher sensitivity to wind. For the irrigation of field crops a 300 angle is common, while for under-canopy irrigation in orchards, the prevalent angles are 40 - 70 . Fig. 2.14. Jet Angles
- 35. SPRINKLER IRRIGATION 14 a. ImpactSprinklers b. Turbo Sprinkler Fig. 2.15. Low-volume Under-canopy Sprinklers 2.5.4 Sprinkler Flow-rate Sprinklers are classified into three groups in respect to their flow-rate. 2.5.4.1. Low flow-rate: 20 - 500 l/h. Used in orchards, greenhouses and gardens. 2.5.4.2. Medium flow-rate: 500 - 5000 l/h. Used mainly for overhead irrigation in field crops, orchards, fodder and vegetables. 2.5.4.3. High flow-rate: Above 5 m3 /h. Used in wide-spacing positioning and mechanized irrigating machines. 2.5.5. Working Pressure (Head) 2.5.5.1. Low pressure: Up to 2 bar (20 m.). Microjets, microsprinklers, mini- sprinklers, whirling sprinklers and turbo-hammer sprinklers. 2.5.5.2. Medium pressure: 2 - 5 bar (20 - 50 m.). Impact sprinklers. 2.5.5.3. High pressure: Above 5 bar (50 m.). Gun sprinklers and large impact sprinklers. 2.5.6. Sprinkler Spacing, Selection And Operation There are a number of elementary factors that have to be considered in the selection of sprinklers according to distinct operating conditions: a. The flow-rate and wetting diameter at different degrees of pressure. b. Crop spacing. c. The desired range of the pressure and the recommended spacing between emitters. d. Soil intake rate. The application rate has to be lower than the soil intake rate. e. Wind conditions during the irrigation season. f. Water quality. (Eq. 2.3) g. Wind velocities in the plot have to be considered in the selection of the sprinkler type as well as the spacing between the sprinklers. As the wind velocity is higher, the
- 36. SPRINKLER IRRIGATION 15 spacing willbe smaller. Table 2.1. Wind Velocity Definitions: No wind 0 - 1.0 m/sec. Medium wind velocity 1.0 - 2.5 m/sec. Strong wind 2.5 - 4.0 m/sec. Very strong wind above 4.0 m/sec. Sprinkler overhead irrigation is not recommended. Table 2.2. Recommended Spacing between Sprinklers Positioning Wind velocity m/sec Spacing No wind 60% of wetting diameter 2 50% of wetting diameter 3.5 40% of wetting diameter Rectangular More than 3.5 30% of wetting diameter No wind 65% of wetting diameter 2 55% of wetting diameter 3.5 45% of wetting diameter Diagonal More than 3.5 30% of wetting diameter The diagonal (staggered) position allows for wider spacing between sprinklers under windy conditions.
- 37. 16 3. MICRO-EMITTERS 3.1. Introduction Theterm micro-irrigation relates to pressurized irrigation technologies employing water emitters with tiny apertures that deliver water at a low flow- rate. The micro-emitters are classified into two principal groups: a. Emitters that distribute water through the air: micro-sprinklers, rotors, spinners, wortex emitters, vibrating emitters, microjets, sprayers, rayjets and foggers. There is no definite difference between sprinklers for irrigation and the micro- emitters that distribute water through the air in micro-irrigation. There is a controversy about the distinction between macro and micro emitters – the common division boundary is 60 – 120 l/h. b. Emitters that deliver the water directly to the soil – drippers and bubblers. These emitters are not covered in this booklet. The primary use of non-drip micro- irrigation technology is for the irrigation of orchards and greenhouses. Unlike sprinkler irrigation of field crops and vegetables, in which the desired result is rain-like uniform distribution over the entire irrigated area, in orchard irrigation, full cover and even distribution of water, is unattainable and is not necessary. The objective of orchard irrigation is to deliver a uniform amount of water to each tree and to distribute it in compliance with the distribution of the root system in the soil. There are still orchards that are irrigated by overhead sprinklers, particularly for frost and hot spell protection. In these orchards, the sprinklers employed are of the same types that are used for irrigation of field crops. Obviously, because of the interference of the canopy in orchards, an even distribution of water on the soil surface cannot be achieved. Overhead irrigation in orchards is favored when frost protection is a significant factor in the selection of the irrigation technology. However there are many drawbacks in the use of overhead sprinkler irrigation in orchards. It interferes with pest management by leaching the pesticides from the canopy and enhances leaf and fruit diseases. The energy consumption in overhead irrigation is higher than in under- canopy irrigation. The dominant technology in orchard pressurized irrigation, therefore, is under-canopy irrigation by low-volume, low-angle sprinklers, mini and micro-sprinklers, as well as microjets, sprayers and drippers. Recently, the use of micro-sprinklers had been extended to irrigation of vegetables and field crops. Micro-sprinklers are commonly built of rigid plastic materials. They are much smaller Fig. 3.1. Diverse Micro-emitters
- 38. 17 and cheaper thanconventional sprinklers. 3.2. Micro-emitter Types There are four emitter types: a. Static Micro-emitters b. Vortex Emitters c. Vibrating Micro-jets d. Micro-sprinklers 3.2.1. Static Micro-emitters (Micro-jets) Static micro-jets have no moving components and are classified into three groups: 3.2.1.1. Sprayers – the water stream is fragmented into tiny droplets by means of a static deflector. Water is distributed in a relatively short range and the tiny drops are wind-sensitive. In sprayers, the deflectors form a fine spray, providing uniform coverage that is essential in sandy soils. They are particularly useful for frost protection. However, they are susceptible to wind and bring about relatively high evaporation losses. The deflectors are produced in diverse styles that allow sector coverage from 450 to 3600 . 3.2.1.2. Misters and Foggers – water droplets are smaller than in sprayers. Spread range is shorter. Wind sensitivity and evaporation losses are higher than in sprayers. This type is mostly used to increase the humidity in greenhouses and poultry coops, as well as for frost protection in orchards. 3.2.1.3. Multi-jet Emitters (Ray-jets, Fan-jets) – the water stream is splitted into 4 – 20 discrete jets. The wetting range is extended and wind sensitivity is reduced. Absence of moving parts increases its reliability compared with rotating micro- sprinklers. a. Static Sprayer b. Ray-jet c. Mister d. Fogger Fig. 3.2. Static Micro-jets
- 39. 18 3.2.1.4. Vortex Emitters Theseemitters have no moving parts. The water whirls in a circular vortex chamber that delivers a low flow-rate through a relatively large opening that reduces clogging hazard. The area wetted by this emitter is smaller than the wetted area by micro-sprinklers. 3.2.1.5. Vibrating Micro-jets Water ejected from a circular orifice strikes a deflector and triggers it to vibrate. The vibration of the deflector creates larger drops than those of sprayers, increases the distribution range and reduces evaporation and sensitivity to wind. The emitter is simple and reliable. 3.2.2. Micro-sprinklers Micro-sprinklers are manufactured in different configurations. Their distinctive characteristic is the rotation of the deflector or the nozzle around a central shaft. This facilitates wetting of larger area, compared with micro-sprayers. However, the inclusion of moving parts increases the susceptibility to the interference of external factors, as well as wear, tear and breakage of its components. During harvest operations, fruit pickers sometimes step on and break micro-sprinkler emitters and stakes. Herbicide spray booms and other tillage equipment can also damage the emitters. Most types of micro-sprinklers are modular. Many components are interchangeable and enable the modification of flow-rate, range, distribution pattern and droplet size, matching to specific requirements, at low cost. Fig. 3.5. Modular Micro-emitter – Water Spreading Pattern Deflectors in diverse configurations allow sectorial coverage from 450 to 3600 . Fig. 3.3. Vortex Sprayer Fig. 3.4. Vibrating Micro-jet
- 40. 19 3.2.3. Micro-sprinkler Types 3.2.3.1.Rotors are manufactured in different configurations. The central shaft with the nozzle is static. The water jet hits a rotating deflector that distributes water in larger area than the vibrating emitters. 3.2.3.2. Spinners - the nozzle rotates and further increases the jet range, that is bigger than that of the rotators. The movement of components in micro-sprinklers increases their sensitivity to the interference of factors like weeds, precipitates and splashed soil particles. It also accelerates wear and tear. The damage danger from herbicide sprayer booms and other tillage equipment increases during harvest operations. Rotors' and spinners' configuration affects their sturdiness. There are two principal forms: unilateral and bi- lateral supports that hold the rotor/spinner swivel. Bi-lateral support provides improved holding to the rotating spinner or deflector, but the two vertical supports create dry sectors behind them. a. Micro-sprinkler Components b. Interchangeable Components Fig. 3.8. Modular Micro-sprinkler a. rotor b. spinner Fig. 3.6. Rotating Micro-sprinklers a. Unilateral Support b. Bi-lateral Support Fig. 3.7. Micro-sprinklers Configurations
- 41. 20 Pressure compensating andflow regulated micro-emitters are particularly suitable for irrigation of steep sloping plots. Micro-sprinkler systems require a higher volume of water supply compared with on- surface or buried drip systems. Dedicated micro-emitters had been developed for use on laterals in mechanized irrigation. They will be related in the chapter on mechanized irrigation. 3.3. Emitter Mounting Emitters can be mounted directly on the lateral, attached by a barbed or threaded protrusion. The most prevailing connection to the lateral is by means of a small diameter micro-tube. The vertical position of the emitter is secured by a stake, stabilizing rod or a weight (in upside-down positioning In greenhouses and mechanized irrigation). The emitter is raised 10 – 25 cm above soil surface to prevent water blockong and disturbance in the rotation of the moving parts of micro-sprinklers by weed interference and splashed soil particles. The micro-tubes are 50 – 100 cm long and 4 – 8 mm in diameter. To prevent excessive head losses, tube diameter of at least 6 - 8 mm is required for emitter flow-rates over 60 l/h and when the micro- tube length is over 60 cm. In greenhouses, micro-sprinklers, misters and foggers are frequently used to increase the relative humidity and lower the temperature of the ambient atmosphere. The misters and the foggers emit tiny droplets and are operated intermittently in pulses. These emitters are often mounted upside-down with the trajectory angle slanted downwards, in order to avoid hitting the glass or plastic ceiling. Threaded micro-emitters are installed on 1 /2 " – 3 /4" rigid PVC risers. Barb micro- emitters can be mounted directly on the lateral. In greenhouses, micro-emitters may be installed upside down for overhead irrigation and misting. Weights are hung to stabilize them vertically. Micro-sprinklers are prone to clogging, but when clogging occurs it is quickly visually noticed and easily cleaned. Some emitters are equipped with a small integral valve to enable local water shut-down during the cleaning process. Some types of micro-sprinklers are prone to clogging by the eggs and excretions of spiders, ants and other insects. Insect-proof devices have been developed to prevent these obstructions. Spiders are capable of tying up spinners and halt their rotation. Micro-sprinkler operation can also be disturbed by sand that is splashed upward from the soil surface when hit by droplets from adjacent emitter. Blockage that is not removed on time in orchards that employ one emitter per tree may result in lower yields and reduced produce quality.
- 42. 21 3.4. Water DistributionPatterns The emitter’s water distribution pattern is determined by its outlet (nozzle) and deflector geometry, trajectory angle, droplet size, pressure and flow-rate. The higher the trajectory angle (up to 300 ) and the larger the droplet size and flow-rate, the larger will be the wetting diameter in the range of the designed working pressure. The patterns of water distribution and wetting depth in the wetted area vary with the emitter type. In some emitters the wetting pattern is triangular. These emitters are suitable for overlapping and full wetting of the soil surface. In some emitters the deeper wetting depth is adjacent to the emitter while in others the water is distributed more evenly in most of the wetted area. a. Sprayer on Stake b. Upside-down Misters with Stabilizing Weights c. Micro-sprinkler on Rod d. Upside-down Micro-sprinkler Fig. 3.9. Mounting Alternatives of Micro-emitters
- 43. 22 Fig. 3.10. WaterDistribution by Micro-sprinkler at Different Flow-rates (example) Fig. 3.11. Multiple-jet (Fan-jet) Emitter's Distribution Patterns From "Bowsmith" Brochure 3.5. Pressure Compensation Micro-sprinklers and micro-jets can be pressure compensating. That facilitates longer laterals and uniform application in harsh topographic conditions.
- 44. SPRINKLER IRRIGATION 23 4. THEIRRIGATION SYSTEM 4.1. Introduction The performance of a pressurized irrigation system depends on the available water sources, reservoirs and pumping facilities. The efficiency of energy use and water application is determines by the properties of the pumping unit and the water delivery and distribution network. 4.1.1. The Main Components of the Irrigation System a. The pumping unit b. Supply pipeline c. Control head d. Mains and sub-mains e. Manifolds f. Laterals g. Risers h. Emitters i. Accessories: Valves, check-valves (backflow preventers), air release valves, vacuum valves, filters, couplers, risers, pressure and flow regulators, fertigation devices, etc. 4.1. The Pumping Unit While the water emitters are the core of the pressurized irrigation system, the pump is its priming element. The pump lifts water from the source (well, river, lake, reservoir, canal, etc.,), increases its energy and governs the capacity and the working pressure in the system. Pumps are activated by electric motors or internal conbustion engines and deliver water under pressure to the irrigation system. Water supply can be attained also from external water suppliers that are responsible for the appropriate pressure head in the connection point with the irrigation system. In some cases, the pressure in the supply connection point is too low and the farmer has to boost the water pressure by means of a booster pump. The energy use efficiency of electric motors is much higher than that of combustion engines. Hence, If electricity is available, it will be the preferred choice. If there is no electricity source, pumps can be operated by a diesel, kerosene or gas motor. The efficiency of the pumping unit is an important factor in water discharge, pressure head and energy costs. Fig. 4.1. Schematic Plot Irrigation System Layout After NDSU Extension Publication Fig. 4.2. Electric Water Pumps
- 45. SPRINKLER IRRIGATION 24 The pumpingunit is composed of three major components: The power unit, the transmission to the pump (drive or gear head) and the pump itself. 4.1.1. Pump Performance Terminology 4.1.1.1 Pump performance - Capacity is expressed as volume per time unit, e.g.: cubic meters per hour (m3 /h) and the pressure as meters (m.) of head. In the imperial unit system it is designated as gallons per minute (gpm) and feets of head. In general, in a specific pump, a trade-off occurs between head and capacity. Increase in head brings about the decrease in capacity and vice versa. 4.1.1.2. Head refers to gains or losses in pressure due to change in topography and friction in the network. The following terms are used when referring to lift or head: 4.1.1.3. Static Suction Lift - The vertical distance from the water surface in the reservoir/well to the centerline of the pump's impeller. 4.1.1.4. Maximum suction lift - Pumps lift water with the support of atmospheric pressure. The practical suction lift, at sea level, is ~10 m. Later on, the pump imparts additional pressure to the water and discharges it from the casing. 4.1.1.5. Static Discharge Head — the vertical distance from the discharge outlet to the point of discharge or liquid level when discharging into the bottom of a tank. 4.1.1.6. Dynamic Suction Head — the static suction lifts plus the friction in the suction line. Also referred to as Total Suction Head. 4.1.1.7. Dynamic Discharge Head — the static discharge head plus the friction in the discharge line. Also referred to as Total Discharge Head. 4.1.1.8. Total Dynamic Head — the Dynamic Suction Head plus the Dynamic Discharge Head. Also referred to as Total Head. 4.1.1.9. Net Positive Suction Head (NPSH) – the head measured in the suction point. 4.1.1.10. Net Positive Suction Head required (NPSHr) - The minimum head requirement in the pump inlet. It takes into consideration head losses in the suction piping and connections, the elevation and absolute pressure of the fluid in the suction piping, the velocity of the fluid and the temperature, including what goes on in the eye of the pump's impeller. Some of these factors add energy to the fluid as it moves into the pump, and others subtract energy from the fluid. There must be sufficient energy in the fluid for the impeller to convert this energy into pressure and flow. If the energy is inadequate we say that the pump suffers inadequate NPSH. The NPSHr is actually the minimum suction pressure necessary to keep the pumped fluid in a liquid state and avoid cavitation in the pump. 4.1.1.11. Net Positive Suction Head available (NPSHa) The head available at the pump inlet. It has to exceed the NPSH required.
- 46. SPRINKLER IRRIGATION 25 4.1.2. PumpTypes There is an extensive selection of pump types. Only a few of them are used in water pumping. Fig. 4.3. Pump Type Classification According to the Hydraulic Institute (HI) Standards All pumps may be divided into two major categories, based on the pattern in which they transmit energy to the pumped fluid: a. Kinetic (dynamic) pumps b. Positive displacement pumps 1) In kinetic pumps, continuously added energy increases the velocity of the fluid. Later on, this velocity is converted into pressure. In centrifugal pumps, energy is imparted to the fluid by centrifugal action, by impeller or lifting action of a screw within a close-clearance bore. 2) In positive displacement pumps, intermittently added energy directly increases the pressure of the fluid. The reciprocating action of one or several pistons, or a squeezing action of diaphragms, meshing gears, lobes, or other moving elements, displaces the pumped fluid from the suction point to the discharge outlet. These pumps have limited capacities and are not suitable for pumping when large volume of water is required for irrigation or drainage. They are used mainly for injection of chemicals into irrigation systems and will be related in the chapter on fertigation. 4.1.2.1. Comparison of the Main Features between Kinetic and Positive Displacement Pumps 4.1.2.1.1. Flow-rate and Pressure Head The two types of pumps behave differently regarding pressure head and flow-rate:
- 47. SPRINKLER IRRIGATION 26 a. TheCentrifugal Pump's flow varies, dependending on the system pressure (head). b. The Positive Displacement Pump's flow is constant, regardless of the system pressure (head). Generally, Positive Displacement Pumps are capable to generate higher pressure than Centrifugal Pumps. 4.1.2.1.2. Capacity and Viscosity Another significant difference between these two pump types is the effect of viscosity on the capacity: a. In Centrifugal Pumps the flow decreases when the viscosity is increased. Centrifugal Pumps are inefficient at even modest viscosity. b. In Positive Displacement Pumps the flow increases when viscosity is increased. Liquids with high viscosity fill the clearances of a Positive Displacement Pump causing a higher volumetric efficiency. The Positive Displacement Pump is better suited for high viscosity applications. That property is irrelevant to pumping of water, since water viscosity changes only slightly as a function of temperature change. 4.1.2.1.3. Mechanical Efficiency The pumps behave in different patterns considering mechanical efficiency. a. In Centrifugal Pumps changes in system pressure (head), affects significantly the flow-rate. b. In Positive Displacement Pumps changes in system pressure have little or no effect on the flow-rate. 4.1.2.1.4. Net Positive Suction Head - NPSH Another difference relates to the Net Positive Suction Head (NPSH). a. In a Centrifugal Pump, NPSH varies as a function of flow determined by pressure. b. In a Positive Displacement Pump, NPSH varies as a function of flow determined by speed. Reducing the speed of the Positive Displacement Pump reduces the NPSH. 4.1.2.1.5. Pump Velocity a. Since in centrifugal pumps the energy is imparted to the liquid by means of centrifugal force, the pressure generated is proportional to the square of the speed of the impeller. b. A positive displacement pump is simply pushing the liquid against whatever resistance that is put on its way. The speed at which it runs is irrelevant – the pressure it can generate is only a function of how mechanically strong the machine is. 4.1.3. Suction Lift of a Pump The theoretical suction lift or suction head is equal to atmospheric pressure divided by the density of the fluid being pumped. In case of plain water (cold) it is 10.33 meters or 33.9 feet. Hence for other fluids maximum suction lift is:
- 48. SPRINKLER IRRIGATION 27 (Eq. 4.1) 4.1.4.Kinetic Pumps Kinetic pumps are dynamic devices that impart the energy of motion (kinetic energy) to a liquid by use of a rotating impeller, propeller, or similar devices. Kinetic pumps are classified into two main groups: a. Centrifugal / Turbine pumps b. Special pump types: centrifugal screw, rotating case, viscous drag and vortex action. 4.1.4.1. Centrifugal Pumps The advantages of centrifugal pumps brought about that they became the pump of choice in water delivery. Compared with positive displacement pumps, the main benefits are smaller size and lower weight. Centrifugal pumps attain much larger flows in a compact device, without pressure and flow pulsations. They are much easier to control, unlike positive displacement pumps in which flow-rate can only be controlled by varying the speed, the flow-rate of a centrifugal pump can be adjusted simply by means of discharge throttling. Centrifugal pumps can be classified by impeller shape and characteristics. Impellers are grouped according to the major direction of flow with respect to the axis of rotation. a. Cutaway b. Pump Components Fig. 4.4. Centrifugal Pump With respect to type of impeller, all centrifugal pumps can be classified into three groups: a. Radial-flow pumps b. Axial-flow pumps c. Mixed-flow pumps Centrifugal pumps can also be classified into four major groups depending on their design and application.
- 49. SPRINKLER IRRIGATION 28 a. Volutepumps b. Turbine pumps c. Diffuser pumps d. Propeller pumps Centrifugal pumps employ a rotating impeller to move water through a piping system. The rotating impeller increases water pressure by transformation of kinetic energy. As water is drawn into the pump, the rotating impeller releases kinetic energy into the water. When the water exits outward through the impeller vanes, the kinetic energy (velocity) is converted into pressure. Centrifugal pumps must be primed by filling them with water before they can be activated. Water has to flow into the pump when pressure at the center (eye) of the impeller is reduced below atmospheric pressure. Volute pumps and Turbine pumps are the two main centrifugal pump categories that control and maintain water pressure differently. 4.1.4.1.1 Volute Centrifugal Pumps The primary difference between volute pumps and turbine pumps is the presence or lack of diffusion vanes. In volute pumps there are no diffusion vanes, but the outer casing is a spiral. This shape reduces water velocity (and eventual pressure) by creating an equal flow of water as it moves around the spiral toward the discharge nozzle. The spiral is called a volute. Volute centrifugal pumps are used to pump from reservoirs, lakes, streams and shallow wells. They are also used as booster pumps in supply and irrigation pipelines. The impeller converts energy from the motor to the water by centrifugal force. The rotation of the impeller develops centrifugal forces that drive the water towards the impeller's external edge. The impeller is surrounded by a volute casing. The volute or stationary diffuser ring converts the kinetic energy into pressure energy and delivers the fluid to the pump discharge outlet. The horsepower input is proportional to the pumping water discharge and the pressure level. As the resistance of a system increases, the head will also increase. This in turn causes the flow-rate to decrease and will eventually reach zero. A zero flow-rate is only acceptable for a short period without causing to the pump to burn-out. Centrifugal pumps are designed for either horizontal or vertical operation. The horizontal configuration employs a vertical impeller connected to horizontal drive shaft. Horizontal centrifugal pumps are the most common in irrigation systems. They are relatively cheap, require less maintenance, easier to install and more accessible for inspection and maintenance than the vertical pumps. Since centrifugal pumps must be "primed" - completely filled with water, before they can operate, the suction line and the pump have to be filled with water and freed of air. Air tight joints and connections are particularly important on the suction pipe. Priming a pump can be done by hand operated secondary vacuum pumps, internal combustion engine or motor powered secondary vacuum pumps. Fig. 4.5. Different Flow Patterns in Centrifugal Pumps From Grundfos Pump Handbook
- 50. SPRINKLER IRRIGATION 29 Vertical centrifugalpumps may be mounted so that the impeller is immersed continuously in the water. In this case, priming is unnecessary. There are self-priming horizontal centrifugal pumps for special purpose use. Self priming is particularly essential where there are frequent electrical power outages. Self priming is requested also with the new generation of control panels for center pivots, where automatic restart is a programmable function. 4.1.4.1.2. Turbine Pumps In a turbine pump, multiple diffusion vanes surround the rotating impeller. As water is released from the center (eye) of the impeller, it spins outwards as the impeller rotates. Around the impeller’s circumference are constructed diffusion vanes - passages that widen gradually and open into a circular or spiral casing. The main role of the diffusion vanes is to gradually reduce the velocity of water. The velocity is transformed into pressure. Once in the outer casing, the water circles around toward the outlet (nozzle), where it exits the pump. Heads over 300 m. are readily developed in a two-stage turbine pump. Vertical turbines have vertical drive shafts and are used to pump water from wells. The impeller has tight axial clearance and pump channel rings that decrease recirculation head losses. The channel rings create a circular channel around the impeller's blades from the inlet to the outlet. The liquid entering the channel from the inlet is picked up immediately by the vanes on both sides of the impeller and pushed through the channel by the shearing action. The repeating process continuously increases the water energy. 4.1.4.1.2.1. Deep Well Turbine Pumps Deep well turbine pumps are used in cased wells or where the water surface is deeper than the practical limits of a volute centrifugal pump. Turbine pumps are also used with surface water systems. Since in this case, the water intake is continuously below the water surface, priming is not needed. Turbine pump efficiencies are comparable to or greater than most volute centrifugal pumps. They are usually more expensive than volute centrifugal pumps and more complicated to inspect and repair. There are two configurations: a. The pump is connected with a vertical gear shaft to a motor on top b. Submersible motor in water-proof case The turbine pump has three main parts: a. Head assembly b. Shaft and column assembly c. Pump bowl assembly Fig. 4.6. Water Flow in Volute Pump
- 51. SPRINKLER IRRIGATION 30 The pumphead is normally made of cast iron and designed to be installed on a foundation. It supports the column, shaft and bowl assemblies and provides a discharge outlet for the water. It supports an electric motor, a right angle gear drive or a belt drive. The shaft and column assembly provides a connection between the head and the pump bowls. The line shaft transfers the power from the motor to the impellers and the column that carries the water to the surface. The line shaft on a turbine pump may be either oil or water lubricated. Oil-lubricated pump has an enclosed shaft into which oil drips, lubricating the bearings. Water-lubricated pump has an open shaft. The bearings are lubricated by the pumped water. If the water contains fine sand, oil lubrication is a must. If the water is for domestic or livestock use, it must be free of oil and a water-lubricated pump have to be used. The impeller is enclosed by the pump bowl. Due to its limited diameter, each impeller develops a relatively low head. In most deep well turbine installations, several bowls are stacked in series one above another. This is called staging. A four-stage bowl assembly contains four impellers, all attached to a common shaft and creates four times the discharge head of a single-stage pump. Impellers used in turbine pumps may be either semi-open or enclosed. The vanes on semi-open impellers are open on the bottom and they rotate with a close tolerance to the bottom of the pump bowl. The tolerance is critical and have to be adjusted when the pump is new. During the initial break-in period the line shaft couplings will tighten, therefore, after about 100 hours of operation, the impeller adjustments should be checked. After a. Motor on Top b. Submersible Fig. 4.7. Deep-well Verical Turbine Pumps
- 52. SPRINKLER IRRIGATION 31 break-in, thetolerance must be checked and adjusted every three to five years or more often if sand is suspended in the pumped water. 4.1.5. Installation of Vertical Turbine Pumps Deep well turbine pumps must have correct alignment between the pump and the power unit. Correct alignment is made easy by using a head assembly that matches the motor and column/pump assembly. The well has to be straight and perpendicular. The pump column assembly must be vertically aligned so that no component touches the well casing. If the pump column does touch the well casing, vibration will wear holes in the casing. A pump column out of vertical alignment may also cause excessive bearing wear. The head assembly must be mounted on a good foundation, at least 12" above the ground surface. A foundation of concrete provides a permanent and trouble-free installation. 4.1.6. Submersible Pumps Submersible pumps are particularly advantageous in pumping from exceptionally deep wells. In a conventional vertical wet-pit pump the motor is mounted on top at the surface, in the open air, driving the pump via a line shaft. The deeper the pump is, the longer the line shaft must be. Long shafts, particularly at high speed rotation, are susceptible to problems of misalignment and the intermediate bearings are prone to wear when there are any abrasive particles in the pumped liquid. Submerged motor drives the pump directly. Pumps can be submerged in depth of 2 km and more. Submersible pumps can be installed in caissons wider only slightly than the pump itself. The limiting factor with regard to the minimum diameter is usually the requirement for sufficient liquid circulation around the pump in order to keep the motor cool. A typical submersible pump is a turbine pump close-coupled to a submersible electric motor. Both pump and motor are suspended in the water, thereby eliminating the long drive shaft and bearing retainers required for a deep well turbine pump with motor on top. The pump is located above the motor, and the water enters the pump through a screen positioned between the pump and the motor. In submersible pumps, enclosed impellers are used because the shaft from the electric motor expands when it heats and pushes up on the impellers. The pump curve for a submersible pump is similar to that of a deep well turbine pump with motor on top. Submersible motors are smaller in diameter and much longer than ordinary motors. Because of their smaller diameter, their efficiency is lower than that of motors used with centrifugal or conventional deep well turbine pumps. Submersible motors are classified as dry or wet motors. Dry motors are hermetically sealed with high Fig. 4.8. Pump Impellers
- 53. SPRINKLER IRRIGATION 32 dielectric oilinside for lubrication, to exclude water from the motor. In wet motors the rotor and bearings are open to the well water and operate inside it. If water circulation through the motor is inadequate, it may overheat and burn out. Therefore, the length of riser pipe must be sufficient to keep the bowl assembly and motor completely submerged always and the well casing must be large enough to allow water to easily flow past the motor. Submersible pumps used for irrigation need three phase electrical power. Electrical wiring from the pump to the surface must be watertight with all connections sealed. Voltage at the motor leads must be within ±10% of the motor nameplate voltage. Because the pump is located inside the well, lightning protection should be wired into the control box. Submersible booster pumps can be mounted horizontally in a pipeline. Occasionally they are used as booster pumps in the suction lines of volute centrifugal pumps, where the water level fluctuates significantly along the season. Having a submersible pump in the suction line will convert the head at the inlet of the volute centrifugal pump from a suction head to a positive head. 4.1.7. Pump Stages The head generated by Volute and turbine pumps depends on the number of stages. Fig. 4.9. Single-stage Pump Fig. 4.10. Multi-stage Pump 4.1.7.1. Single-stage Pump a. It has one impeller keyed to the shaft. This is generally horizontal but can be vertical also. b. It is usually a low lift pump. 4.1.7.2. Multi-stage pump a. It has two or more impellers keyed to a single shaft and enclosed in the same casing. Pressure is built up in steps. b. The impellers are surrounded by guide vanes and the water is led through a by-pass channel from the outlet of one stage to the entrance of the next stage until it is finally discharged into a wide chamber from where it is pushed on to the delivery pipe. c. Multi-stage pumps are used essentially for high working head and the number of stages depends on the head required.
- 54. SPRINKLER IRRIGATION 33 4.1.8. SolarWater Pumps and Solar Water Pumping Systems DC powered pumps, are used in typical solar electric systems that have an inverter available. DC powered pumps are used for deep and shallow well pumping, stock tanks, irrigation and many other applications. DC pumps are different in many properties from the AC pumps that are ordinarily used in water delivery systems. DC pumps come in a variety of types: small pressure booster pumps, diaphragm and piston positive displacement pumps for wells, booster pumps, circulating pumps, groundwater sampling pumps etc. These low-power pumps allow building a solar pumping system for a deep well at a modest cost. They are cheaper than windmill operated pumps, and have peak output during dry, sunny weather when water is needed most. They can be installed and pulled by hand. They can pump from wells of very low yield that conventional pumps may suck dry in minutes. Pumps are available that pump as low as 120 l. per hour. Solar energy operated pumps require a dedicated controllers if they are to be powered directly by Photo Voltaic (PV) modules without battery backup. 4.1.9. Variable Speed Drives For years, the common means for decreasing excessive water pumping beyond the requested amount were throttling by valves or release of the excess water to reservoirs. These two techniques are energy wasteful and pose hazard of damage to the water system by excessive pressure. Nowadays, Variable Speed Drives (VSDs), known also as Variable Frequency Drives (VFDs), are extensively used in water pumping. They control the discharge by changing the velocity (rpm) of the impeller/turbine according to water demand and keep the pump operating at high energetic efficiency. It also protects the pump from mechanical damage by excessive pressure and enhances its mechanical reliability. The old fashion valve throttling is expensive, contributes to higher energy and maintenance costs, and impairs control loop performance. Employing a throttled control valve, less than 50% open, on the pump discharge outlet, may accelerate component wear and slow valve response. Since Variable Frequency Drives allow pumps to run at slower speeds, the Mean Time Between Failures (MTBF) is extended. Fig. 4.11. Solar Pumping System Fog. 4.12. A Variable-frequency Drive Controlls a Set of 3 Pumps
- 55. SPRINKLER IRRIGATION 34 4.1.10. Selectingan Efficient Pumping Plant The efficiencies of individual pump types vary among types, manufacturers and models. The minimum acceptable pump efficiency is in the range 75-85%. Once the operating pressure (head) and system capacity (in m3 /h) have been determined, pump characteristic curves should be consulted to select the most efficient pump for the specific requirements. 4.1.10.1. Power-unit Efficiency. Power-unit efficiency is important in pumping plant performance. As mentioned before, power sources are of two types: (a) internal combustion engines (either direct drive engines used solely for irrigation or tractors equipped with a power takeoff to drive pumps) and (b) electric motors. Power-unit efficiency is the efficiency with which chemical energy stored in the fuel (for internal combustion engines) or electrical energy (for electric motors) is converted to mechanical energy to drive the pump. Where electricity is available, it is the most efficient power source. The efficiency of electric motors ranges from about 80% for motors under 7.5 hp. to over 90% for motors of 75 hp. or more. Internal combustion engines are much less efficient. Diesel engine efficiencies range is 25-37% and kerosine engines are only 20-26% efficient. The difference in operating costs among various types of power units and pumps over the lifetime of the pumping plant, must be weighed against any savings in initial investment. 4.1.10.2. The Pump Efficiency (ηηηη) The efficiency of a pump is determined by its hydraulic and mechanical performance. It is defined as the ratio of the useful power delivered by the pump (Water Kilowatts) to the power supplied to the pump shaft (brake horsepower). The efficiency of the pump is expressed as percentage or decimal fraction. 4.1.11. Maintaining Irrigation System Efficiency Well-designed irrigation systems with properly sized pumping plants will normally meet or exceed performance standards during initial use. However, over the lifetime of the system, mechanical components of the system wear, reducing the overall effficiency of the system. The common causes of low overall effficiency are discussed below. 4.1.11.1. Internal Combustion Engines. Each percentage decrease in engine efficiency increases fuel consumption by 3-5%. Pump engines should be tuned-up at the beginning of each irrigation season to ensure effficient performance. Air and fuel filters should be changed at manufacturers' recommended intervals. 4.1.11.2. Electric Motors. A buildup of dirt or oil, obstruction of cooling vents, worn or dragging motor bearings, and voltage surges caused by lightnings can cause electric motors to overheat. Overheating often leads to shorted wires in the winding and is the most common cause of low motor efficiency. Voltage surges can also cause damage to or misalignment of phases in three-phase motors, resulting in low motor efficiency. Misaligned shafts between motor and pump and over-tightened packing glands or seals can also reduce efficiency. Low efficiency caused by extended use (wear) can sometimes be corrected by replacing the accumulator brushes or having the motor rewound. In the case of small motors (20 - 25 hp. or less) it is usually more practical to replace the entire motor. Electric motors should be
- 56. SPRINKLER IRRIGATION 35 protected fromrain and direct sunlight. 4.1.11.3. Matching System Components. Often, irrigation systems are altered from their original design, resulting in mismatching of components. Alterations such as adding or deleting sprinklers or laterals are often made without making corresponding adjustments to the pumping plant. A change in the depth of water in deep wells where the static head has declined, can alter the pumping conditions so that the pump no longer operates in the desired efficiency range. In some cases, the pump can be adjusted to resume operation within the recommended range. On turbine pumps the bowls can be adjusted and the impellers trimmed. If wear is excessive, bowls and impellers should be replaced. If an internal combustion engine is used, the system can sometimes be adjusted by changing the operating speed. 4.1.12. The Pumping Unit Efficiency The overall "wire-to-water" efficiency of a pumping plant is the relationship between the energy consumed (in kWh) and the amount of water or other fluid being delivered (m3 /h) at a given pumping head (m.). The greater the overall efficiency of the pumping plant, the lower the overall pumping costs will be. The efficiency of the pumping unit depende on the efficiency of its 3 comonents: the power unit (electric motor or internal combustion engine), the pump and the transmission between them. The efficiency is the ratio of the output energy to the energy of input to the system. The output and the Input are expressed in terms of Water Kilowattes (WKW) of power being generated by the pump. WKW = Flow x TDH / 360 (Eq. 4.1) Where: Flow is in m3 /h TDH (Total Dynamic Head, another term for pressure) at the Best Efficiency Point (BEP) on the pump curve is expressed in m. of water head. Hence: WKW = m3 /h Χ TDH/360 As mentioned before, the efficiency of electric motors is 75% - 95%. Internal combustion engines are much less efficient. Kerosine engines efficiencies is 20 – 26% and in diesel engines 25% - 37%. The efficiency of the transmission system (gears, shafts, pulleys, etc.) that transmit power to the pump can approach 95% – 97%. The efficiency of the pump itself is in the range of 75% - 85%. Efficiency under 70% commits checking and repairing the pump. Thus, the potential efficiency of an electric powered pumping plant if correctly designed, installed, and maintained is in the range of: (75% - 85%) x (95% - 97%) x (75% - 85%) = 60% - 70%
- 57. SPRINKLER IRRIGATION 36 Referring tothe example in the curve at right, and putting in the numbers : M3 / HR X TDH / 360 = 68 x 76 / 360 = 14.36 WKW. The curve shows a 60% efficiency so: 14.36 water kilowatts / 0.60 efficiency = 23.93 Kilowatts required. If this number is lower than shown on the pump performance curve, the efficiency of the plump is questionable. As an example: If the pump performance curve showed a requirement for a 30 Kilowatt input, the actual efficiency would be: 14.36 water horse power / 30 Kilowatts required = 48 % actual efficiency. A pump can operate over a wide range of flow and pressure combinations. That is, the same pump may be able to draw 250 m3 /h at 20 m. head pressure or 125 m3 /h at 30 m. head. However, each combination of flow and pressure (the combination is termed the “operating condition”) will result in a different pump efficiency. E.g., at 240 m3 /h and 20 m. head, the pump may be operating at 80% efficiency. However, at 120 m3 /h and 30 m. head it is operating at only 65% efficiency. These differences in efficiency are due to the physics of water flow through an individual pump, while a specific flow-rate may result in more or less turbulence than another. 4.1.12.1. Power Units The pump drive transmits power from the power generating unit to the pump. The line shaft of electric-driven pumps is connected directly to the motor shaft, eliminating the need for a pump drive. When the pump is driven by an internal combustion engine, the pump drive is a right-angle gear drive, that may change the RPM of the pump. The efficiency of a right-angle gear drive is about 95%. Belt drives may vary in efficiency from 85 to 95%. Calculation of the power requested on the pump shaft Q X HN = 270Xἠ (Eq. 4.2) Where: N = the requested power (HP) Q = the pump discharge - m3 /h. H = total required head (lift+friction losses+topographic losses+working pressure) m. (1 m. = 0.1 bar). ηηηη = the pump efficiency (decimal fraction). Conversion of the HP. Units to KW units as it is customary with electric motors is attainable by the ratio 1 HP = 0.7457 KW. Fig. 4.13. Pump Efficiency Curve
- 58. SPRINKLER IRRIGATION 37 4.1.13. Cavitation Cavitationcan damage pumps, valves and other accessories. Pump cavitation is the formation of cavities on the back surface of an impeller, resulting in loss of contact between the impeller and the water being pumped (Walker, 1972). Cavitation occurs when the local static pressure is below the vapor pressure of the fluid. After the water enters a pump, its velocity increases, causing decrease in the head within the pumping unit. If the head falls too low, the water will vaporize, forming bubbles in the liquid. These bubbles collapse violently as they move to areas of higher pressure. The collapse of the bubbles occurs at sonic speed ejecting destructive micro jets of extremely high velocity, up to 1000 m/s, strong enough to cause severe wear of the pump components, particularly impellers. Pressure reduction occurs due to: a. inadequate submergence of the pump water intake; b. too high impeller speed that creates extremely low pressure behind the impeller; c. constrained pump intake route; d. high water temperatures which decrease the pressure needed to vaporize the water. As mentioned before, the pressure required to operate a pump satisfactorily and avoid cavitation is called Net Positive Suction Head (NPSH). The head available at the pump inlet has to exceed the NPSH required (NPSHr). The required NPSH is specified by the pump manufacturer. Cavitation is a common problem in pumps and control valves - causing serious wear, and damage. In pumps, Impeller surfaces and pump bowls will pit and wear. Cavitation reduces the life-time expectancy of the components. This may happen when the fluid accelerates in a control valve or around a pump impeller. 4.1.14. Pump Curves Pump manufacturers provide for each pump a set of curves from which The performance of the pump can be evaluated. In selecting a pump, one of the concerns is to optimize pumping efficiency. It is good practice to examine several performance charts at different velocities to learn if a specific model is more efficient than others. Whenever possible, the lowest pump speed should be selected, as this will decrease wear and tear of the rotating components. The available curves are: Performance, Efficiency, Horsepower¸ NPSH Requirement and System curve. Fig. 4.14. A Scheme of Pump Curves
- 59. SPRINKLER IRRIGATION 38 4.1.14.1. PerformanceCurve A performance curve is a plot of Total Head vs. flow-rate for a specific impeller diameter and speed. The plot starts at zero flow. The head at this point corresponds to the shut-off head of the pump. Starting at this point, the head decreases until it reaches its minimum. This point is sometimes called the run-out point and represents the maximum flow of the pump. Beyond this, the pump cannot operate. 4.1.14.2. Efficiency Curves The pump's efficiency varies throughout its operating range. This information is essential for calculating the motor power. The B.E.P. (Best Efficiency Point) is the point of highest efficiency of the pump. All points to the right or left of the B.E.P have a lower efficiency. The impeller is subject to axial and radial forces, which get greater the further away the operating point is from the B.E.P. These forces manifest themselves as vibration dependent on the speed and construction of the pump. The point where the forces and vibration levels are minimal is at the B.E.P. Fig. 4.15. An Example of Pump Curves Plotted on One sheet 4.1.14.3. Horse-power Curves The horse-power curves are shown on the chart and give the power required to operate the pump within a certain range. For example (Fig. 4.16.), all points on the performance curve to the left of the 2 hp curve will be compatible with a 2 hp motor. All points to the left of 3 hp curve and to the right of the 2 hp curve will fit to a 3 hp motor. The horsepower can be calculated from data of the Total Head, flow and efficiency at Fig. 4.16. Horse-power Curves
- 60. SPRINKLER IRRIGATION 39 the operatingpoint. 4.1.14.4. N.P.S.H. Requirement Curves The pump manufacturer specifies the minimum NPSH required (NPSHr). in order for the pump to operate at its designed capacity. The NPSHr becomes higher as flow increases, and lower as flow decreases. The meaning is that more pressure head is required at the pump suction for high flow than for low flow. Since NPSH is a head term, it is independent of the fluid density and is expressed as absolute fluid column height. 4.1.14.5. System Curve The system curve is a plot of the Total Head vs. the flow for a given system. The higher the flow, the greater the head required. The shape of the system curve depends on the type of system being considered. The system curve is superimposed on the pump performance chart. The Total Static head is constant and the friction head, equipment head and velocity head are flow dependent. The calculation of Total Head at different flow-rates produces a plot of Total Head vs. flow that is called the system curve. The operating point is the point on the system curve corresponding to the flow and head required. It is also the point where the system curve intersects the performance curve. The design system curve is usually calculated with some extra flow capacity 4.1.15. Pump and Well Testing Pump testing is an important testing procedure. It is typically done when the pump is disconnected from the irrigation system. A flow-meter, pressure indicator and valve are installed on the pump exit. The pump is started and the valve is gradually partially closed, until the design system pressure is attained. The system is allowed to run for a period of 15 minutes, and then the valve is fully opened and closed again in order to obtain enough points to draw a pressure / flow curve. The static water level should be recorded at each flow point. The net positive suction pressure of the pump should be determined to ensure that the pump is immersed deep enough in the well to prevent cavitation. It is recommended that pumps and wells will be tested every 2 years when are operated full-season. Fig. 4.17. Critical Points on the Pump Curve
- 61. SPRINKLER IRRIGATION 40 5. PIPESAND ACCESSORIES 5.1. Introduction In pressurized water supply and irrigation systems, Water delivery and distribution is done by means of pipes and tubes. Actually, a pipe is a hollow cylinder in a specified length. Most pipes have circular cross-section. Pipes may be also of rectangular cross-section, but those pipes are used in construction and not for water delivery. Apart from water delivery, pipes are used for conveying different fluids – oil, gas, slurry, industrial liquid compounds and in some circumstances also powders. The terms pipe and tube are commonly used interchangeably. In most of the world the common term is pipe. In the USA, there is a distinction between pipes that are manufactured to international or national standards and are specified by outer nominal diameter and schedule that indicate the wall thickness. Tubes are made to custom sizes, in a broader range of diameters and tolerances and are specified by outer diameter (OD), inside diameter (ID) and the exerted wall thickness. In pipes the schedule indicates the wall thickness that determines the allowed working pressure. In tubes, the working pressure is defined more explicitly by the class definition of the allowed working pressure in bars or kilopascals (KPa). Pipes are made of a variety of materials: Metals: cast iron, ductile cast iron, carbon steel, galvanized steel, wrought steel, stainless steel, aluminum and copper. Concrete, ceramic and compound materials: reinforced concrete, ceramic, asbestos cement. Plastic: PolyVinyl Chloride (PVC), UPVC (Unplasticised PVC), CPVC (Chlorinated PVC), PolyEthylene (PE), PolyPropylene (PP), Glass Reinforced Polyester (GRP). 5.2. Pipe materials 5.2.1. Iron, Steel and Copper Cast iron was in extensive use in the early years of pressurized irrigation. Due to its vulnerability to corrosion, its life expectancy time-length was relatively short. Pitting and rust accumulation on the inner wall surface decreased the wall smoothness and increased friction head losses in the flowing liquid. Ductile cast iron had improved pipe performance but corrosion remained a severe disturbance. Carbon steel further improved pipe functioning. Later on, in order to avoid corrosion, the inner wall surface was coated by reinforced cement that kept wall smoothness and prevented corrosion. Steel pipes are expensive and are used mainly in water supply networks. In underground installed pipes, the outer wall surface is coated with asphalt, to avoid damage to the outer surface by corrosive elements in the soil. Stainless steel is too expensive to be used in irrigation and water supply networks. Copper is used mainly in residential and industrial plumbing. In irrigation systems, copper small diameter tubes are utilized in hydraulic control devices of automated systems. Galvanized tin pipes were used in the past in hand-move irrigation but were replaced by aluminum pipes.
- 62. SPRINKLER IRRIGATION 41 5.2.2. Aluminum Theuse of aluminum pipes for irrigation commenced after WWII. They replaced the galvanized tin pipes used in hand-move irrigation. Their low weight and sturdiness eased the operation of hand-move systems. High quality pipes were manufactured from corrosion resistant aluminum known as alclad aluminum. Aluminum pipes are manufactured in two technologies. In one of them, pipes are produced from aluminum flat sheets that are rounded and welded. The other technology is extrusion, in which seamless pipes are produced. 5.2.3. Asbestos-cement Pipes made of asbestos-cement were in wide-scale use in water supply networks and as mains for irrigation. The use of these pipes is now prohibited because it was found that asbestos fibers are carcinogenic, endanger workers in the production line and may disintegrate by some chemicals inherent in the water and endanger the users. 5.2.4. Concrete Concrete pipes are used mainly in drainage and sewage systems. 5.2.5. Plastic Materials 5.2.5.1. Overview After the introduction of aluminum pipes that were used mainly in hand-move irrigation, began the production of pipes made from plastic materials for use as replacement of galvanized iron pipes as laterals and single emitter extensions as well as replacement to carbon-steel pipes in water supply networks and as distributing mains, sub-mains and manifolds in the irrigated parcels. Plastics are solid materials comprised of one or more polymeric substances that can be shaped by molding or extrusion. Polymers, the basic ingredient of plastic materials, are a broad class of materials that include natural and synthetic substances. In professional terminology, polymers are frequently defined as resins. For example, a PolyEthylene (PE) pipe compound consists of PE resin combined with colorants, stabilizers, anti-oxidants and other ingredients required to protect and enhance the quality of the material during the fabrication process and the operation in the field. Plastic materials are divided into two basic groups: thermoplastics and thermosets, both of which are used for the production of plastic pipes. Thermoplastics include PolyEthylene (PE), PolyPropylene (PP), PolyButylene and PolyVynil Cloride (PVC). These materials can be re-melted by heat. The solid state of thermoplastic materials is the result of physical forces that immobilize polymer chains and inhibit them from slipping past each other. When heat is applied, these forces weaken and allow the material to soften or melt. Upon cooling, the molecular chains stop slipping and are held firmly against each other in the solid state. Thermoplastics can be shaped during the molten phase of the resin and therefore can be extruded or molded into a variety of shapes, such as pipes, flanges, valves, sprinklers and micro- sprinklers components, drippers and other accessories. Thermoset plastic materials are similar to thermoplastics prior to a chemical reaction (“curing”) by which the polymer chains are chemically bonded to each other by new
- 63. SPRINKLER IRRIGATION 42 cross-links. Thatis usually performed during or right after shaping of the final product. Cross-linking is the random bonding of molecules to each other to form a giant three- dimensional association. Thermoset resins form a permanent insoluble and infusible shape after applying heat or a curing agent. They cannot be re-melted after shaping and curing. This is the main difference between thermosets and thermoplastics. As heat is applied to a thermoset component, degradation occurs at a temperature lower than the melting point. Thermosetting resins can be combined with reinforcements to form strong composites. Fiberglass is the most popular reinforcement and fiberglass- reinforced pipes (FRP and GRP) are a common form of thermoset-type pipes. 5.2.5.2. Polyethylene Polyethylene (PE) is the most prevalent material in pipes and laterals in pressurized irrigation systems. There are four types of PE, classified by material density: Type I – Low Density (LDPE), 910 – 925 g/l Type II – Medium Density (MDPE), 920 – 940 g/l Type III – High Density (HDPE), 941 – 959 g/l Type IIII – High Homo-polymer, 960 and above g/l Two percent, by weight, of carbon black agent are added to increase pipes’ resistance to the detrimental impact of exposure to ultraviolet (UV) sun radiation. Another classification relates to the working pressure that the pipe withstands (PN). Common grades of PN used in irrigation are: 2.5, 4, 6, 10, 12.5 and 16 bars (atm). Certain thin-walled laterals withstand lower PN: 0.5 – 2 bar. The pressure tolerance depends on pipe material density and wall thickness. Tolerance data published by the manufacturers relate to standard temperature of 20 C0 . At higher temperatures, the tolerance decreases significantly, hence pipes are tested at twice the designated working pressure. Plastic pipes are designated according to their external diameter, in mm. In the USA and some other countries, pipe diameter is marked in imperial inch units (“). 1” = 25.4 mm. Pipe wall thickness is designated in mm units (in the USA by mil units. Mil = 1/1000 of inch). 1 mil = 0.0254 mm. Laterals are commonly made of LDPE (PE – 32 grade) while delivering and distributing pipes of diameters greater than 32 mm are mostly made of HDPE. HDPE pipes are further classified according the grade of the material: PE-63, PE-80, PE-100. The higher the grade, the higher the pipe quality and pressure tolerance. Table 5.1. PE (PolyEthylene) Pipes for Agriculture PE type ND (Nominal Diameter) Applications PN - m LDPE 6 mm Hydraulic command tubing 40 – 120 LDPE 4 – 10 mm Micro-emitter connection to laterals 40 – 60 LDPE 12 – 25 mm Thin-wall drip laterals 5 – 20 LDPE 12 – 25 mm Thick-wall drip laterals 25 – 40 LDPE 16 – 32 mm Micro and mini emitter laterals 40 – 60 HDPE 32 – 75 mm Sprinkler laterals 40 – 60 HDPE 40 – 140 mm Main lines and submains 40 – 100 HDPE 75 – 450 mm Water supply and delivery networks 60 - 160
- 64. SPRINKLER IRRIGATION 43 Table 5.2.LDPE Pipes Internal (Inner) Diameter and Wall Thickness - mm PN OD ↓↓↓↓ 25 m 40 m 60 m 80 m 100 m mm ID Wall thickness ID Wall thickness ID Wall thickness ID Wall thickness ID Wall thickness 12 9.8 1.1 9.6 1.2 9.2 1.4 8.6 1.7 8.0 2.0 16 13.2 1.4 12.8 1.6 12.4 1.8 11.6 2.2 10.6 2.7 20 17.0 1.5 16.6 1.7 15.4 2.3 14.4 2.8 13.2 3.4 25 21.8 1.6 21.2 1.9 19.4 2.8 18.0 3.5 16.6 4.2 32 28.8 1.6 27.2 2.4 24.8 3.6 23.2 4.4 21.2 5.4 40 36.2 1.9 34.0 3.0 31.0 4.5 29.0 5.5 26.6 6.7 50 45.2 2.4 42.6 3.7 38.8 5.6 36.2 6.9 33.4 8.3 Adapted form Plastro brochure ND = Nominal Diameter OD = External (Outer) Diameter. In plastic pipes, mostly equivalent to the ND. ID = Internal (inner) Diameter Table 5.3. HDPE Pipes Internal (Inner) Diameter and Wall Thickness - mm Adapted form "Plastro" brochure 5.2.5.3. PVC Pipes PVC (PolyVinyl Chloride) is a rigid polymer. Addition of plasticizers renders flexibility to tubes made of soft PVC. PVC pipes are sensitive to UV sun radiation. Soft and flexible, they are used mainly in gardening and landscape. In agriculture and water supply systems, rigid PVC pipes are mainly used for water delivery and distribution. PVC pipes are installed only underground to avoid damage from UV radiation. Currently, un-plasticized PVC (UPVC) pipes are manufactured with improved UV and pressure surges tolerance. PVC pipes appear in discrete 4 – 8 m long segments and have to be attached in the field. The working pressure of rigid PVC pipes is 6 – 24 bars (60 – 240 m). PN OD 25 m 40 m 60 m 80 m 100 m 160 m mm ID Wall thickness ID Wall thickness ID Wall thickness ID Wall thickness ID Wall thickness ID Wall thickness 12 8.6 1.7 16 12.8 1.6 11.6 2.2 20 16.8 1.6 16.2 1.9 15.4 2.8 25 21.8 1.6 21.1 1.9 20.4 2.3 18.0 3.5 32 28.8 1.6 28.2 1.9 27.2 2.4 26.2 2.9 23.2 4.4 40 36.8 1.6 35.2 2.4 34.0 3.0 32.6 3.7 29.0 5.5 50 46.8 1.6 46.0 2.0 44.0 3.0 42.6 3.7 40.8 4.6 36.2 6.9 63 59.8 1.6 58.2 2.4 55.4 3.7 53.6 4.7 51.4 5.8 45.8 8.6 75 71.2 1.9 69.2 2.9 66.0 4.7 64.0 5.5 61.4 6.8 54.4 10.3 90 85.6 2.2 83.0 3.5 79.2 5.5 76.8 6.6 73.6 8.2 65.4 12.3 110 104.6 2.7 101.6 4.2 96.8 6.6 93.8 8.1 90.0 10.0 79.8 15.1 125 118.8 3.1 115.4 4.8 110.2 8.1 106.6 9.2 102.2 11.4 90.8 17.1 140 133.0 3.5 129.2 5.4 123.4 9.2 119.4 10.3 114.6 12.7 101.6 19.2 160 152.0 4.0 147.6 6.2 141.0 10.3 136.4 11.8 130.8 14.6 180 172.2 4.4 166.2 6.9 158.6 11.8 153.4 13.3 147.2 16.4
- 65. SPRINKLER IRRIGATION 44 Table 5.4.PVC Pipes for Agriculture PVC type ND Applications PN - m Soft PVC 6 mm Hydraulic command tubing 40 – 80 Soft PVC 6 – 10 mm Micro-emitter connection to laterals 40 – 60 Soft PVC 12 – 25 mm Tapes and thin-wall drip laterals 5 – 20 Rigid UPVC ½” – 4” Risers 40 – 100 Rigid UPVC 63 – 1000 mm Supply networks, main lines, submains 40 – 240 When PVC pipes are installed in heavy or stony soil, it is recommended to pad the trench with sand to prevent damage to the pipe wall by swelling soil pressure and contact with sharp protrusions of stones. Table 5.5. Internal Diameter and Wall Thickness of PVC Pipes PN------> 60 m 80 m 100 m OD - mm ID - mm Wall thickness - mm ID - mm Wall thickness - mm ID - mm Wall thickness - mm 63 59.0 2.0 58.2 2.4 57.0 3.0 75 70.4 2.3 69.2 2.9 67.8 3.6 90 84.4 2.8 83.0 3.5 81.4 4.3 110 103.2 3.4 101.6 4.2 99.4 5.3 140 131.4 4.3 129.2 5.4 126.6 6.7 160 150.2 4.9 147.6 6.2 144.6 7.7 225 210.2 6.9 207.8 8.6 203.4 10.8 280 262.8 8.6 258.6 10.7 253.2 13.4 315 295.6 9.7 290.8 12.1 285.0 15.0 355 333.2 10.9 327.8 13.6 321.2 16.9 400 375.4 12.3 369.4 15.3 361.8 19.1 450 422.4 13.8 415.6 17.2 407.0 21.5 500 469.4 15.3 461.8 19.1 452.2 23.9 5.2.5.3.1. Lay-flat Hoses Flexible PVC lay-flat hoses can be used as mainlines and sub-mains as well as feeding pipes in mechanized irrigation systems. The hose is impregnated with anti- UV radiation protecting agents. When the water is shut-off, the hose lays flat on the ground and can be crossed-over by tractors and other farm machinery. The lay-flat hoses can be laid out on the soil surface or in a shallow trench. These hoses are available in diameters of 75 – 200 mm. 5.2.5.4. Fiberglass Pipes In addition to UPVC and HDPE pipes, reinforced fiberglass pipes are used to deliver water under high pressure from the water source to the irrigated area, as a substitution for steel and asbestos-cement pipes. GRP (Glass Reinforced Polyester) fiberglass pipes are manufactured in diameters of 300 – 3600 mm and PN grades of 40 – 250 m. They are particularly useful in delivery of reclaimed water.
- 66. SPRINKLER IRRIGATION 45 5.3. Externaland Internal Pipe Diameter The internal diameter (ID) of a pipe can be calculated by deducting twice the wall thickness from the external diameter (OD). In most cases, the designated nominal pipe diameter (ND) is its external diameter. Friction head losses of water flow in the pipe are determined by the internal diameter. It is imperative to check whether the designated diameter is nominal (mostly external) or internal, when using nomograms, on-line calculators and design software.
- 67. SPRINKLER IRRIGATION 46 6. COUPLERS 6.1.Connectors (Fittings) Connectors are made of metal or plastic materials. They may be two-sided straight- through or angular units, T or Y shaped triple outlets, four-sided crosses or multi- outlet splitters. 6.1.1. Aluminum Couplers Aluminum couplers are used for connecting two pipes. In some couplers there are outlets for sprinkler risers. a. Hermetic Couplers b. Detached Band Coupler c. Elbow Fig. 6.1. Hermetic and Detached Band Couplers Hermetic couplers are used to connect pipes in main supply lines and sub-mains that will be laid in the field at least for one whole season. Dual band couplers are widely used. They are manufactured in diameters of 1.5, 2, 3, 4, 5 and 6".The coupler is attached to the pipe by means of two clamps and two rings. There are rubber seals at both the inlet and the outlet of the coupler to prevent leakage during irrigation and to facilitate drainage after water shut-off. There are distinct seals for high and for low pressure. The couplers are reliable, easily detached from the pipe for transportation on trailers, symmetrical in construction and easy to assemble. In towlines the couplers are affixed to the wheels or to slide supports. Drainage of the pipe after water shut- off can be accomplished through a drain valve that is mounted in the middle of the pipe Fig. 6.2. Single Latch Couplers Single latch couplers are manufactured in 1, 1.5, 2, 3, and 4" diameters. They are permanently fixed by screws at the end of the pipe. They are used mainly in hand- move and tow systems, due to their convenient dismantling.
- 68. SPRINKLER IRRIGATION 47 In eachstyle of couplers there are different models such as starter elbows for connecting the lateral to the hydrant; elbows; reducing adapters for changing diameters, end plugs, etc. Adapters made of Al-Pb metal alloy should be installed as an isolating interface between aluminum couplers to components made of other metals to prevent the fusion of the metal with the aluminum. For hand-move laterals in high-canopy crops, like maize, there are quick couplers that facilitate fast disconnecting of the riser from the lateral. Risers are made of galvanized iron, aluminum or P.V.C. One or both edges are threaded. The common risers for sprinklers are of ½", ¾” and 1” diameter. Fig. 6.5. Aluminum Lateral Assembly 6.1.2. Polypropylene Couplers Fig, 6.6. Plastic and Metal Connectors Their functions are identical to those of aluminum couplers. They are manufactured in diverse sizes and shapes. Fig. 6.3. Valve Adapters Fig. 6.4. Adapter Made of Al-Pb Metal Alloy
- 69. SPRINKLER IRRIGATION 48 There aretwo main groups: external and internal couplers. In the external type, the pipe is inserted into the coupler and is held by one or more grooved rings. The internal type is inserted inside between two pipe segments. There is also a combination of the two methods - external and internal fasteners in one unit. The external type is the most prevalent form used in sprinkler irrigation. These couplers are cheap, manufactured from rigid plastic materials such as polypropylene, which provide strength and endurance. Sprinklers are attached to the laterals in three modes: a. On a riser fastened into a saddle fitting, mounted straight on the lateral. The saddle has to guarantee the vertical position of the riser. b. By means of a tube and a vertical support that allows a certain flexibility in spacing. This type of connection ensures the vertical position of the sprinkler independently of the position of the lateral. c. Directly on a saddle. Couplers have diverse forms like head elbows, "T", angle, etc. Quick bayonet couplers are used for connection of risers to aluminum and plastic pipes, to valves and other diverse water outlets. Fig. 6.7. Lock Fastened Polypropylene Connectors a. Polypropylene b. Aluminum Fig.6.8. On-line Saddles
- 70. 49 SPRINKLER IRRIGATION 7. REGULATIONAND CONTROL 7.1 Introduction An important advantage of pressurized irrigation over surface irrigation is the ease and convenience of regulation and control of the given water amount. The most basic level of regulation is accomplished by: a. Selection of competent equipment according to the requirements of water flow capacity and working pressure grade of pipes, water distribution pattern of emitters, etc. b. Manual opening and shutting of the water flow. 7.2. Supply Pipelines The supply pipeline delivers the water from the source to the irrigated plot. The pipes are made of coated or non- coated steel or plastic materials like P.V.C., Polyethylene, Polypropylene and fiberglass. The diameter of the supply pipeline ranges from 3” (75 mm) to 14” (350 mm) diameter. The pipes have to resist pressure surges. The working pressure ranges from 8 to 20 bar (80 – 200 m.). Contemporary water supply networks are monitored and controlled by sophisticated equipment that facilitates efficient water supply and billing, when applicable More advanced levels of control employ automatic valves and controllers, pressure and flow regulators, air-release and vacuum valves, check valves, computers and communication devices 7.3. The Control Head The control head is composed of the accessories that manage the irrigation and the fertigation process. A basic control head may contain the valve and a filter, if needed. The more sophisticated control heads contain a computerized controller, fertilizer injector, pressure regulator, air-release valve, etc. Fig. 7.1. Water Supply Network Fig. 7.1. Typical Control Head
- 71. 50 SPRINKLER IRRIGATION 7.4. Regulationand Control Devices 7.4.1. Valves Valves control the flow of the water in irrigation systems. Valves are used for on/off control, regulation of pressure and flow rate and the prevention of back-flow. Valves can be operated manually or automatically by means of mechanical, hydraulic or electrical mechanisms. There are diverse types of valves that have been developed for miscellaneous service requirements. Fig. 7.3. Valve Types 7.4.1.1. Valve Actuators Valves can be operated manually or automatically by means of mechanical, hydraulic or electrical actuators. Fig. 7.4. . Manual Actuators
- 72. 51 SPRINKLER IRRIGATION 7.4.1.2. GlobeValves The globe valve is the most prevailing valve used in irrigation systems. Its name stems from it globular appearance. In addition to on/off tasks, globe valves are used for throttling and flow control. They demonstrate linear flow response to partial closing. They can be kept open in any degree from fully open to fully closed. The globe valve is controlled by a rising-shaft. The construction of the valve drives the water to make two 90°turns when passing throug h the fully open valve. Hence, pressure losses in the globe valve are higher than in a fully open gate and ball valves. Significant pressure loss is the main drawback of this valve type. a. Schematic View b. Direct-flow Body c. Y Body Fig. 7.5. Globe Valve The major components of globe valves are: a. The body. b. The bonnet. c. The valve seat and valve plug, or trim. d. The valve spindle (stem) which connects to the actuator. e. The sealing assembly between the valve stem and the bonnet. The principal pattern of globe valve operation is the perpendicular movement of the disk away from the seat. When the disk approaches gradually to the seat ring, the valve is gradually closing. This way of work provides the globe valve good throttling capability for flow regulation. Generally, globe valve yields much less seat leakage than gate valves. The disk-to-seat ring contact is better at right angle and that ensures the tight sealing in shut-off mode. 7.4.1.2.1. Types of Globe valves Globe valves are manufactured in three forms: a. Line valve with straight flow pattern – The connections (flanges or threads) are along the same line. b. Y valve - the connections are in the same line, however the valve disc and the valve plate together are at an angle and the outward shape is of the English letter “Y.” c. Angular valve – The inlet and the outlet have a 900 angle between them. Fig. 7.6. Angular Valve
- 73. 52 SPRINKLER IRRIGATION Most globevalves are built with a single seat. In large globe valves, delivering high volume of water, much force is requested on the actuator for shut-off. If that force is not available (with some electric or hydraulic actuators) a modified double seat valve is requested. Fig. 7.7. Single-seat Globe Valve Adapted from Control Valves by Spirax Sarco Fig. 7.8. Double-seat Globe Valve Adapted from Control Valves by Spirax Sarco The double-seat valve has two valve plugs on a common spindle, with two valve seats. The valve seats can be kept smaller and the forces are partially balanced. Although the differential pressure is trying to keep the top valve plug off its seat, it is also trying to push down and close the lower valve plug, so, the force needed for shut-off is smaller than in single-seat valve. Globe valves are built from bronze, cast iron, steel and plastic materials. They are operated by manual or hydraulic actuators. 7.4.1.2.2. Advantages of Globe Valves a. Long service life. b. Very little valve lift is required to attain full flow (unlike gate valves). c. A change in direction of the fluid flow can be done (unlike gate valves) in the angular valve type. 7.4.1.2.3. Drawbacks of Globe Valves a. High head losses caused by the diverted water flow. b. Large valves require considerable power to operate. c. Relatively heavy weight compared with other valves with the same flow rating. d. Large opening necessary for the disk assembly. e. Cantilevered mounting of the disk to the stem. 7.4.1.3. Angle and "Y" Valves Angle and "Y" valves have less pressure losses than direct-flow globe valves. In the angle valve there are fewer angles compared to the globe valve and the water makes only one 90°turn. In the "Y" valve the water has t o turn twice, as in the globe valve, however, the angles are of 45° only. The flow path is nearly as free as in the gate valve.
- 74. 53 SPRINKLER IRRIGATION 7.4.1.4. GateValves The gate valves are used mainly for on/off service. They are not suitable for gradual opening and closing tasks. A disk or wedge attached to the valve spindle regulates the water flow. The common type has a rising- spindle that facilitates visual indication how far the valve is open, since the threaded portion of the spindle is exposed. The on/off action is slow. Faster action can be achieved by sliding the spindle up or down with support of a mechanical lever. Since most of the shut-off activity takes place when the valve is almost closed, the flow control profile is not linear. That poses difficulties to regulate the water flow in a partially open position. 7.4.1.5. Ball Valves The ball valve is compact and employs a spherical flow control element. It is operated in 90° rotations. When fully opened, the b all valve has a full flow pattern with minimum head losses. Due to the non-linear flow nature in partial closing, ball valves are used only for on-off tasks and not for flow regulation unless specifically designed for throttling. a. Side View b. Diagonal View Fig. 7.10. Ball Valve Cutaway a. Side View b. Cutaway Fig. 7.9. Gate Valve
- 75. 54 SPRINKLER IRRIGATION 7.4.1.6. ButterflyValves In a butterfly valve, the flow-control element is a disk pivoted on an axis in the valve casing. The disk is turned parallel to the flowing water when the valve is fully open, resulting in small friction losses. Butterfly valves are simple and compact, and have good throttling capability. The flow response to the shut-off of the flow control element is not linear. Butterfly valves offer economy, particularly in larger sizes and in terms of flow capacity per invested money. Big butterfly valves require large or high-output actuators (if are actuated hydraulically or electrically). Soft-seat assembly is obtained by means of a rubber liner or by an adjustable soft ring in the body or on the face of the disk. 7.4.1.7. Piston Valves Piston valves have a piston-shaped closure member that intrudes into or withdraws from the seat bore. The sealing takes place between the lateral faces of the piston and the seat bore. A fluid-tight contact between these faces is attained by a packing that forms part of the valve bore or the piston. When the valve is being opened, flow cannot start until the piston has been completely withdrawn from the seat bore. When the valve is being closed, the piston tends to wipe away any solids that had been deposited on the seat. Piston valves may handle fluids that carry solids in suspension. If damage occurs to the seating, the piston and the seat can be replaced on the place. Like globe valves, piston valves allow good flow control. If precise flow adjustment is required, the piston may be fitted with a needle shaped extension. Piston valves are also used for stopping and starting flow when flow resistance due to tortuous flow occurs. 7.4.1.8. Diaphragm Valves Diaphragm valves are flex-body valves in which the valve is composed of a rigid and flexible sections. The flexible section is consisted of a diaphragm which, in connection with an actuator, represents the closure member. In diaphragm valves the flow passage is not obstructed by moving parts and is free of crevices. a. Cutaway b. Main Components Fig. 7.11. Butterfly Valve Fig. 7.12. Piston Valve
- 76. 55 SPRINKLER IRRIGATION The seatis a rigid body section and may consist of: a. A weir across the flow passage, or b. The wall of a straight-through flow passage. The weir in the flow passage is designed to reduce flexing of the diaphragm to a minimum, in order to guarantee long diaphragm life, while providing a smooth and streamlined flow passage. The short stroke of the valve permits the use of plastics such as PTFE for the diaphragm. The back of the diaphragm is lined with an elastomer, which supports a uniform seating stress during valve closure. Since the diaphragm area is large compared with the flow passage, the fluid pressure imposes a correspondingly high force on the raised diaphragm. Diaphragm valves with a straight- through flow passage require a more flexible diaphragm than weir-type diaphragm valves. In weir-type diaphragm valves the water is separated from the shaft and shaft collar by the flexible diaphragm. The diaphragm is forced against the weir to close the valve. The fully open valve has only small pressure losses. Fig. 7.15. Diaphragm Valve Working Pattern 7.4.2. Control Valves – Functioning and Actuation In addition to simple tasks of water opening, shut-off and flow throttling, valves accomplish more complicated tasks like: flow-metering, flow and head regulation, backflow prevention, air-release from the pipes, fertilizer injection, filter flushing, etc. Fig. 7.13. Diaphragm Valve Components Adapted from Valve Types by Valvias a. Weir Type b. Straight-through Type Fig. 7.14. Diaphragm Valves
- 77. 56 SPRINKLER IRRIGATION Since themid-fifties, many valves are controlled by programmed controllers and computers. The operation instructions actuate the valves by means of hydraulic or electric actuators. There are also small diameter control valves that are actuated mechanically by the inherent water flow in the valve Fig. 7.16. Control Valves Actuators These control valves are combinations of valves and actuators. The most prevalent valves are of the flexible diaphragm type that is controlled by an electric valve (solenoid) or hydraulic actuator. Piston valves are used in smaller scale. Power to the actuators is transmitted as an electrical current through wires, through wireless devices or as hydraulic pressure through small diameter tubes. The controllers are classified as normally open (NO) and normally closed (NC) groups. Normally Open means that the valve remains open when the power source is off. The normally closed type remains closed when the power source is off. The normally closed type is safer since when the power supply is impaired, the water is closed. On the other hand, this type has greater pressure losses. 7.4.2.1. Electric Control of Hydraulic Valves In many cases, the driving power of the control element is hydraulic pressure that is activated by the electrical current delivered to the actuator. The flow control element can be in the form of a piston that shuts and opens the flow path in the valve. The piston actuator can also serve as a flow regulator. 7.4.2.1.1. Solenoids The solenoid valve, which is commonly used in irrigation systems, employs an electromagnetic force to drive the piston directly or to activate the piloting action that opens the valve. The conversion of electric pulses into mechanical energy by which the actuator closes or opens the water is done by means of solenoids. Solenoid actuated valves provide for automatic open- close valve positioning. Most solenoid actuated valves have a manual override that Fig. 7.17. Cutaway of Solenoid Valves
- 78. 57 SPRINKLER IRRIGATION allows manualoperation of the valve. Solenoids position the valve by attracting a magnetic slug attached to the valve stem. In single solenoid valves, spring pressure acts against the motion of the slug when power is applied to the solenoid. These valves can be arranged such that power to the solenoid either opens or closes the valve. When power to the solenoid is removed, the spring returns the valve to the opposite position. Two solenoids can be used in one valve to apply both opening and closing by switching power to the appropriate solenoid. Single solenoid valves are termed fail open or fail closed depending on the position of the valve when the solenoid is de-energized. Fail open solenoid valves are opened by spring pressure and closed by energizing the solenoid. Fail closed solenoid valves are closed by spring pressure and opened by energizing the solenoid. Double solenoid valves typically fail "as is." That is, the valve position does not change when both solenoids are de-energized. Modern solenoid valves offer fast operation, high reliability, long service life, and compact design. a. Fail-closed (Normally Closed) b. Fail-open (Normally Open) Fig. 7.18. Scheme of Solenoid Operation Fig. 7.19. Fail-closed (NC) Solenoid Valve – Components and Working Pattern In one working procedure, the solenoid is acting directly on the main valve. In other cases, a small, fully functioning solenoid valve known as a pilot is used to actuate a larger valve. While the second type is actually a solenoid valve combined with a
- 79. 58 SPRINKLER IRRIGATION hydraulically actuatedvalve, they are sold and packaged as a single unit referred to as a solenoid valve. Piloted valves require much less power to be activated, but they are noticeably slower. Piloted solenoids usually need full power at all times to open and stay open, where a direct acting solenoid may only need full power for a short period of time to open it, and only low power to hold it open. a. Blow-out b. Working Pattern Fig. 7.20. Hydraulic Control Valve 7.4.2.2. Hydraulic Control of Valves The structure of a hydraulic controller or actuator is similar to that of the electrical control valve but the power is transmitted by a pressure change above the diaphragm or piston actuator. This change of pressure is transmitted through the hydraulic control tubing or by partial diversion of water flowing through the valve. Most of the hydraulic control valves are normally open. Functionally, hydraulic valves, like the electrical ones, fall into two categories: Normally Open (N.O.) and Normally Closed (N.C.). a. Normally Open (N.O.) valve stays open until the control chamber is filled with water under system pressure. When the chamber is full, the valve shuts-off. b. Normally Closed (N.C.) valve is kept closed by the water pressure in the mainline. In case of a rupture in the command line, the closure is secured by pressure of a spring. The valve is opened when a tiny valve at the top of the control chamber opens, releasing water from the control chamber into the atmosphere. Normally closed hydraulic valves have higher head losses, but they are safer to use, as the valve remains closed even if the command tube is torn or plugged. 7.4.3. Check-valves Check valves are used to prevent the back-flow of water in irrigation and water supply networks. The control element has a variety of forms: ball, disk lift, tilting disk, flipper or a swinging disk. The water passage is kept open by the pressure of the water flowing in the ordinary direction. It blocks the passage for back-flow by the gravity force or by spring action when the pressure downstream is higher than upstream. The pressure caused by back-flow or the weight of a water column in the pipe presses the control element against the seat to seal the passage and prevent flow in the reverse direction.
- 80. 59 SPRINKLER IRRIGATION a. Check-valveb. Check-valve Cross-section c. Dual Back-flow Check-valve Fig. 7.21. Check Valves 7.4.4. Pressure Relief Valves Fig. 7.22. Pilot-controlled Hydraulic Pressure Relief Valves Pressure relief valves protect the irrigation network from excessive pressure. They are opened quickly and release small amounts of water to relieve excess pressure in the system. They can be closed by means of a spring-loaded disc or hydraulic pressure. In some types of valves, the spring can be adjusted to a predetermined pressure limit. Excess pressure partially opens the valve and releases some water. Fast Pressure Relief Valves are automatic control valves designed to provide a solution to the typical problems associated with spring loaded relief valves when constant drifting of relief adjustment occurs. The valve is comprised of accurate relief pressure setting that remains constant, opening to full capacity on minimum pressure rise in the pipe line. Regulated rate of closure provides smooth closure without causing pressure surges.
- 81. 60 SPRINKLER IRRIGATION The Pilotscan be grouped to 3 sets: 7.4.4.1. Pressure Reducing Pilot Valve It is a direct acting pilot valve, actuated by a pressure responsive diaphragm, which seeks to reach equilibrium between hydraulic and set spring forces. When used in a pressure reducing circuit, The pilot-modulate closes as downstream pressure rises above set point. An internal restriction device acts as an upstream flow restrictor. 7.4.4.2. Pressure sustaining pilot valve This is a 2-way direct acting pilot valve, actuated by a pressure responsive diaphragm, which seeks to reach equilibrium between hydraulic and set spring forces. 7.4.4.3. Fast Pressure Relief Pilot Valve This pilot integrates all principal functions of a 2-Way control circuit in a single assembly. It is a direct acting pilot valve, actuated by a pressure responsive diaphragm, which seeks to reach equilibrium between hydraulic and set spring forces. The pilot opens as upstream pressure rise above set point. 7.4.5. Pressure Regulators a. Pressure Regulator–Blow-out b. Six Unit Assembly c. Hydraulic Controlled Pressure Regulator d. Pressure Regulators of Different Capacities Fig. 7.24. Pressure Regulators Pressure regulators are used where low and constant pressure is necessary for the proper function of pressure sensitive components, such as laterals and emitters. They are used in systems with pressure fluctuations to maintain constant pressure downstream of the regulator. Pressure regulators are also used in harsh topography conditions for equalizing the head in emtters. There are two types of pressure regulators. Simple mechanical devices regulate the pressure against a spring, while Fig. 7.23. Pilot Valves
- 82. 61 SPRINKLER IRRIGATION in themore sophisticated devices the pressure is controlled hydraulically by a diaphragm or piston. The pressure regulator’s structure is similar to that of the diaphragm and spring- loaded relief valve. The water flow is throttled by the action of a spring at the top of the diaphragm and the counter-pressure of the water on the lower face of the diaphragm. The water from the high-pressure side of the valve is diverted into the chamber above the diaphragm to compensate for the compression of the spring as the upstream pressure changes. This action throttles the controlling valve and keeps the pressure at the preset level. 7.4.6. Air-release Valves Trapped air is a critical problem in irrigation and water supply networks and may cause severe damage to certain components of the system. Air intrudes into the system when pumping is primed or when the water is shut-off by the main valve and the local valves remain open. The air enters through the emitters into the drained network. At the start of the irrigation event, the flow of air through the water-meter may bias the metering and in extreme cases may heat and melt the impeller blades. Another effect of trapped air in pipelines is the water hammer caused by the compressed air that may burst the pipes if the pressure surge surpasses the working pressure of the system. Prevention of trapped air damage can be attained by the use of air- release valves. The valves should be installed in the higher points in the irrigation system, where the trapped air is accumulating in the pipelines. The air-release valve acts by means of a float. When the pipeline is empty or partially full with water, the float is lying down leaving the orifice in the top of the casing open, enabling the flow of air outside and inside. After the system had been filled with water, the float takes its upper position and seals the aperture. There are two basic types of air-release valves: Table 7.1. Flow-rate of Spring Actuated Pressure Regulators Flow-rate – m3 /hModel Min. Max Low flow-rate 0.11 3.0 (one spring) 0.8 5.0 (2 Springs) 1.6 10.0 2" X 4 (4 Springs) 3.2 20.0 2" X 6 (6 Springs) 4.8 30.0 3" X 10 (10 Springs) 8.0 50.0 Fig. 7.25. Cross Section of Air-release Valves
- 83. 62 SPRINKLER IRRIGATION 7.4.6.1. KineticAir Valve This valve is designed to release large amounts of air under low pressure. It is useful at the beginning of the irrigation event when large amounts of air have to be released from the system in a short time. It is also used to enable the high volume back-flow of air into the network after the water shut-off, in order to avoid a vacuum in the pipelines. This valve is not functional at high pressure conditions, when the system has been completely filled with water. 7.4.6.2. Automatic Air Valve This valve functions in low as well as in high-pressure conditions, but it can release only small volume of air. Its main function is to release the small amounts of air that are liberated from the water due to changes in temperature and pressure during the irrigation term. 7.4.6.3. Combined Air Valve This valve incorporates the two air valve types in the same housing and can fully answer the changing demands for air-release from irrigation networks as well as suction of air when water is shut-off. 7.4.7. Atmospheric Vacuum Breakers These are small devices, ½” – 1” in diameter that break the vacuum at water shut-off and do not allow air to escape from the system when water drains from the irrigation system and the pressure in the pipelines falls below the atmospheric pressure. Air relief valves introduce air into the irrigation system when its pressure equals or falls below the atmospheric pressure and function as vacuum breakers. 7.5. Valve Capacity Water flowing through a valve looses energy by the friction with the valve walls and its other components. When the free passage cross- section area is larger, wall smoothness is higher and the bends in the flow way are fewer, the capacity of the valve will be higher. By convention, the flow factor (Kv) relates to the hourly discharge that causes head-loss of 10 m. (1 atm). Where: Kv – Flow Factor (m3 /h at 1.0 bar pressure drop) Q – Flow-rate (m3 /h) Dp – Pressure drop (bar) S – Specific gravity of the fluid (for water = 1.0) 7.6. Automation 7.6.1. Overview In modern irrigation systems, automation is an essential constituent of the operating system. It saves manpower and facilitates precise and on-time application of water and nutrients. a. Flow State b. Non-flow State Fig. 7.26. Atmospheric Vacuum Breakers (Eq. 7.1)
- 84. 63 SPRINKLER IRRIGATION Automation relieson four basic components: sensing and measuring devices; control and regulation appliances; input and output tools; and communication between the different components. Time and quantity controllers are the two basic tools of automation. 7.6.1.1. Classification Automation systems can be classified according to the extent of control: a. Point automation means an automatic device mounted directly on the valve, exclusively controlling this valve with no relevance to other valves or systems. b. Local automation: Several valves in the plot that are controlled and coordinated by one unit. c. Central automation: A number of local automation units that are connected to and controlled by a main central unit. 7.6.1.2. Functions Automation can be activated at diverse levels of sophistication: a. Shut-off of water flow. Water opening is done manually. b. Time-based automatic opening and shut-off of the water. c. Time determined irrigation start according to time, shut-off after a preset water amount had been delivered. d. As above plus feedback and recording of the delivered water amount. e. Control of irrigation combined with fertilizer application (fertigation), with or without recording of water and fertilizer amounts. f. Sequential operation of valves, one after another, in the plot. g. Irrigation control that relies on information obtained from monitors and sensors. E.g.: Temperature, wind, rain, soil moisture, water head etc. h. Control of water sources in correspondence with irrigation demands. i. Integrated control of water sources and irrigation. j. Integrated design and operation and control of irrigation systems. 7.6.2. Flow-meters a. Waltman Flow-meter b. Flow-meter Cross-section c. Flow-meter with Electric Output Fig. 7.27. Flow-meters
- 85. 64 SPRINKLER IRRIGATION The flow-meteris the basic appliance for the monitoring and control of water application in pressurized irrigation systems. It is the only means that facilitate irrigation control in quantitative terms. The common flow-meter consists of a casing containing a horizontal or vertical impeller. The impeller is rotated by the flowing water and transmits its rotational motion to a measuring scale mounted on top of the casing. The scale is calibrated and counts the actual water quantity that passed through the casing. The flow-meter displays the readings of the delivered water amount visually or, by means of an electric output device, sends the information to irrigation controllers, computers or data-loggers. 7.6.3. Metering-valves (Hydrometers) The metering-valve is a combination of a water meter with a hydraulic valve. The desired volume of water to be applied is dialed in. The valve is closed automatically after the assigned volume of water has been delivered. The actuator in the metering- valve can be of diaphragm or piston type. A diaphragm is less sensitive to dirt in the water, but can be torn in pressure surges and may wear due to chemical degradation. The hydrometer can be operated manually or controlled by a remote computer or controller by means of hydraulic, electric or wireless communication. 7.6.4. Control Patterns Two basic types of control patterns that are applied in irrigation systems: a. Open control loop systems that implement only a preset action. b. Closed control loop systems that collect feedback from sensors, make decisions and apply the decisions to the irrigation system. 7.6.4.1. Open-control Loop Systems In open control loop systems, decisions are taken by the operator who presets the controller according to the desired performance. The devices that require external manual intervention are referred to as open loop systems. In time-based open loop control systems, the irrigation duration is preset. The basic control parameters are irrigation timing, intervals and Fig. 7.28. Hydrometers – Cross-section From Bermad Brochure Fig. 7.29. Hydrometer – Manual and Remote-controlled Dial From Bermad Brochure
- 86. 65 SPRINKLER IRRIGATION watering time-span.A combination of time and amount-control employs the clock to start the irrigation and terminates the irrigation after the preset volume of water has been applied. Open loop control systems are inexpensive, readily available and flexible but require frequent manual resetting to attain efficient water application. 7.6.4.2. Closed-control Loop Systems In a closed-control loop, the operator presets the general layout. The control system makes the decisions when and how much water to apply. Feedback is sent in real-time to the controller from one or more sensor units. Closed loop controllers acquire environmental parameters, such as soil-moisture, temperature, radiation, wind-velocity and relative humidity. The data are compared to the preset program and the decision is made whether irrigation should be applied or not. The decision can be based on the measurement of soil-moisture and calculation of the water consumption of the plants. 7.6.5. Irrigation Timers An irrigation timer is based on a clock unit that activates one or more units of the irrigation system at preset times. Irrigation timers may provide several of the following functions: a. A clock/timer measures the time for the irrigation schedule. b. A calendar selector allows presetting the days in which the system has to be operated. c. Station time setting allows the presetting of start time, day and hour and duration of application for each station. d. Manual start allows the operator to start the automatic cycle, overriding the preset schedule. e. Manual operation of each station allows the operator to manually start the irrigation cycle without changing the preset schedule. f. Master switch controls the activation of the whole irrigation system. g. Station skip is used to exclude specified stations from the next irrigation cycle. h. Master valve controls back-flow prevention equipment and automatically terminates irrigation in case of a failure in the system. i. Pump start lead connects the pump start solenoid to the actuator of each station. Thus the pumping control is synchronized with the irrigation control. The timers can be electromechanical or electronic. 7.6.5.1. Electromechanical Controllers Electromechanical controllers are based on an electrically powered clock and mechanical switching to activate the irrigation valves. They are reliable and are not affected by spikes in the power supply. In case of power outage, the programmed schedule will not be erased. However, the scheduling options are limited, compared with electronic controllers. 7.6.5.2. Electronic Controllers Electronic controllers rely on solid state and integrated circuits to actuate the clock/timer, memory and control functions. Some of these systems are sensitive
- 87. 66 SPRINKLER IRRIGATION to thetrustworthiness of the power supply and to spikes, surges and brownouts. These controllers are modular and contain many options at a relatively low cost. Time-based devices are widely used in home-gardens, nurseries and propagation houses. Irrigation lasts for relatively short periods, and lack of precision in water amount, due to pressure fluctuations, is not crucial. Improved accuracy can be maintained by keeping constant pressure with the combination of a buster pump and pressure regulators. 7.6.6. Computer-based Irrigation Control Systems A computer-based control system consists of a combination of hardware and software that manages both irrigation and fertigation by a closed control loop. The system monitors the measured variables, compares them with the target status, makes decisions about the actions to be taken and carries them out. 7.6.6.1. Sensors A sensor is closing an electrical circuit response to change in a specific measured parameter. There are two basic types of sensors: a. continuous b. discrete. 7.6.6.1.1. Continuous sensors transmit a continuous electrical signal, such as voltage, conductivity, capacitance, or any other measurable electrical current. Continuous sensors are used where values taken by a state variable are required and an on/off state is not sufficient, for example, to measure pressure fluctuations in the system. 7.6.6.1.2. Discrete sensors are basically mechanical or electronic switches that indicate on/off states. Discrete sensors are useful for indicating thresholds, such as the opening and shut-off of devices. They can indicate when a threshold of a state variable has been reached. Examples of discrete sensors are a float switch in a storage tank and a switching tensiometer that detects if soil moisture is above a defined threshold. The variables measured in computer-based control systems are: Flow rate, pressure, soil- moisture, air temperature, wind velocity, solar radiation, relative humidity, electrical conductivity and the pH level of the irrigation water. 7.6.6.2. A/D Interface Since computer systems work internally with digits, the electrical signals sent from the sensors have to be converted from analog to digital data. The conversion is accomplished by Analog-to-Digital (A/D) interfaces. Discrete signals resulting from switch closures and threshold measurements are registered in memory. Continuous electrical (analog) signals are converted to binary numbers of the sensed variable. Conversion accuracy is affected by the resolution of the conversion equipment. 7.6.6.3. Computer Types The A/D conversion hardware is directly connected to the computer system. The computer system may be a PC or a dedicated programmed controller. 7.6.6.4. Functions of the Central Computer The fast development and price drop of microcomputers enables high sophistication in automatic control of irrigation. The new irrigation computers and controllers use industry standard microprocessors as well as standard memory boards and
- 88. 67 SPRINKLER IRRIGATION terminals. Thisconfiguration enhances the integration of irrigation scheduling, operation and control at the same unit. Conditional operation, relating to the feedback information that is transmitted from the local units and from sensing units in the field, is now a common routine, as well as the integrated management of the whole irrigation system, from water source to the last end-valve in the field. 7.6.6.5. Communication Apart from point automation, in which the automation control unit is mounted directly on the end valve, in all other automation systems, a communication link connects sensors with the control unit to the end valve. In some circumstances, a multi-stage communication linking is necessary. Signals between the control unit and the end units can be sent as hydraulic or electric pulses. The electric pulses can be transmitted by wire or wireless. In some circumstances, for short distance, hydraulic communication is advantageous compared with electric communication. There is no need for an external energy source and in hydraulically operated wide-diameter valves; there is no need for conversion of electric signals to hydraulic signals by means of solenoid. The control water tube of 4 - 8 mm. diameter pipe is cheaper than electric cable. The drawbacks of hydraulic communication are topography interference, vulnerability to mechanical damage and air penetration. In the past the length of communication lines was restricted to a few hundred meters. Latelr-on, accessories have been developed that facilitate longer lines and overcome the topographic differences. Another drawback of hydraulic communication is the one-way communication pattern that does not enable transmission of feedback information back to the main unit. Electric pulses can be transmitted by cables or by wireless devices. Cable communications are prone to mechanical damage. Due to cost reduction, improved credibility and elimination of broadcasting interference, the wireless communications are favored on cable communications. Direct operation of the end-valves by electric pulses takes place only in home- gardens and nurseries, where valves are usually of small diameter. In wide- diameter valves the operation of the valve is hydraulic. The electric signal is converted by means of a small solenoid that controls operating water supply to the hydraulic valve. 7.6.6.6. Configuration Local automatic systems control the irrigation time- table and the fertigation device. In sequential automatic systems, a main controlling unit is optional. In sequential irrigation, the shut-off of one hydraulic valve sends a hydraulic signal which opens the subsequent hydraulic valve. In more sophisticated systems, the sequence is controlled by a central controller. There are two basic models of wired central automation: a. Star b. Ring Fig. 7.30. Local Irrigation Controller
- 89. 68 SPRINKLER IRRIGATION 7.6.6.6.1. StarConfiguration each local unit is connected directly to the central unit. The cable is of the twin- wire type that enables the central unit to send signals as well as to supply energy to the field units. If feedback information is required, a triple-wire cable has to be installed. 7.6.6.6.2. Ring Networks All the field units are chain connected in a ring by one cable to the central unit. The cable is of the multi-wire type in which each local unit is connected by two or three wires to the central unit. Another setup is based on twin-wire cable. Both the two cables are connected to each one of the local units. The computer of the central unit is scanning continuously the local units with high frequency pulses, identifying each unit, feeding it with the relevant information and picking up feedback information. In this configuration, the field equipment is cheaper but a high level computer is required. In the last decade, most of the wired communication systems are replaced by wireless ones. 7.6.7. Supervisory Control And Data Acquisition (SCADA) In the last decade, Supervisory Control And Data Acquisition (SCADA) software applications in Water & Irrigation systems are increasingly used. The SCADA system is a remote control and status indicator of the water distribution equipment that provides early warning of system malfunction. When failure occurs there is immediate detection of water leakages and pressure fluctuations. This enables immediate response to changes in demand, maintenance of adequate pressure, flow-rates, pump-functionality and overall system performance. Fig. 7.31. SCADA Control System Adapted Adapted from "Motorola" Brochure Sophisticated SCADA systems support various communication infrastructures:
- 90. 69 SPRINKLER IRRIGATION a. RadioCommunication Channels: conventional VHF (136-174 MHz), conventional UHF (403-470 MHz), 800/900 MHz, Microwave, Digital Radio, Cellular Networks, Satellite Systems, Wi-Fi (WLAN) systems, Spread Spectrum b. Wire Line: point-to-point, multi-drop, auto-answer/dial-up operation over PSTN lines. c. Ethernet (TCP/IP): Direct connection to a 10baseT Intranet that will be provided by the user. d. Serial Communication: RS-232 and RS-485 Communication to an external DTE/DCE device. The use of advanced communication protocols, sophisticated RTUs (Remote Terminal Units), contemporary control center software packages and utilization of the internet, improves the overall performance of the Water Distribution system by providing: a. Enhanced control and monitoring of pump & valve stations (as well as other stations and output types) b. Prompt access to data for managers and operators, wherever they are located (at a station, the control room or any other place) from the control center’s alarms and reports c. Graphical User Interface (GUI), which provides a user-friendly and intuitive interface with the control constituents. d. Full monitoring and control of field elements (valves, pumps and other I/O status/failures etc) e. Equipment’s operation 1. Water supply conditions 2. Other conditions and controlled elements 3. Reports and historical data f. Water supply (daily, weekly, monthly, yearly, etc.) 1. Water pressure, low, level, quality etc. 2. Pump operation, valve operation, etc. 3. Power consumption (overall/per pump) g. Alarms 1. Pump failures (overload, temperature, etc.) 2. Power supply failures Fig. 7.32. RTUs Connected to Field-unit (FU) by Cable Adapted from Motorola Brochure
- 91. 70 SPRINKLER IRRIGATION 3. Suddenpressure changes, water quality variations, etc. Due to the miniaturization of the electronic components, the wireless broadcasters, transmitters and receivers, the recently developed field units are compact and reliable. 7.6.7.1. Field Units The field units are the end points of the automation system. They include RTUs that directly control the valves, fertigation device, etc; or connected to sensors of soil moisture, chemicals in soil solution and climate. Field Units (FU) that can connect several RTUs enable higher level of control. When many RTUs and/or FUs are connected to one control center, Field Interface Unit (FIU) can be used as the communication interface unit between the control center and the RTUs or FUs. It will be located at the control room and connected to the computer/server via a serial line. The FIU communicates with the RTUs and the FUS over the available project’s communication links (radio, line etc). Many types of I/O (Input/Output) modules are available (Digital Input, Digital Output, Analog Input, Analog Output, Mixed Digital and Analog Inputs and Outputs etc.) enabling simple connection to diverse measuring and control devices such as hydraulically or electrically operated valves, water meters, flow and level meters, rain gauges, EC/pH sensors, flushing filters etc., as well as other devices (relays, general alarm contacts, analog sensors etc.) 7.6.7.2. Internet Mediated Communication In the last decade, the internet provided new capabilities for SCADA communication. Using wireless internet communication enable central and local control, monitoring and data acquisition from any point on the globe, without distance limits. Fig. 7.33. Internet Mediated SCADA Network Adapted from Motorola Brochure
- 92. SPRINKLER IRRIGATION 71 8. WATERTREATMENT AND FILTRATION 8.1. Introduction Irrigation water quality is defined by its physical, chemical and biological characteristics. The introduction pf micro-irrigation, in particular drip irrigation, posed new challenges for water treatment and filtration. The narrow water passageways in the micro-emitters are exceptionally sensitive to irrigation water quality and are prone to clogging. Although the water passageways in conventional sprinklers are much wider than those of the micro-emitters, the utilization of the new developed filters and the adoption of strict water treatment, improved the performance of sprinkler irrigation systems too. Water pumped from ponds, lakes, rivers, streams, canals and dam reservoirs, contains high loads of impurities. Water pumped from sand aquifers contains great amounts of suspended sand. Sand and silt separation is often performed as a pre-treatment in settling ponds and tanks or by vortex sand separators. a. Physical Quality Parameters: 1. Suspended solid mineral particles 2. Organic matter 3. Live zooplankton b. Chemical Quality Parameters: 1. Salt content 2. The concentration of precipitate-forming ions 3. pH level 4. Nutrition elements content c. Emitter Clogging Factors 1. Particulate matter 2. Biological living organisms and their debris 3. Chemical precipitates 4. Combinations of the above mentioned factors Poor system design and management increase the hazard of emitter clogging. Preventive water treatments against clogging are comprised of sedimentation, filtration and complimentary chemical treatments. 8.2. Particulate Matter Sprinklers are prone to clogging by relatively big solid particles but suspended organic matter can stuck to some components and upset the rotating motion. Micro- emitters are clogged by particles of sand, limestone and other debris too large to pass through the narrow water passageways. Clogging may also occur when small particles stick together to form larger aggregates. Even tiny particles such as suspended clay, which would not cause problems as discrete particles, can initiate clogging if they flocculate to form larger aggregates. Suspended sand particles in the water can cause wearing of the shaft and metallic nozzles in sprinklers. 8.3. Biological Substances Emitters can be clogged by particles of organic matter that block the water passageways. Clogging may be induced by secretions of organisms such as algae and microscopic bacteria. Certain algae are small enough to pass through filters and
- 93. SPRINKLER IRRIGATION 72 emitter passagewaysas discrete entities, but may flocculate in pipelines to form aggregates large enough to clog emitters. Bacteria are small and do not cause clogging; however, they can precipitate compounds of iron, sulfur and other chemical secretions that clog the emitters. Some bacteria secrete slime that acts as an adhesive platform for the buildup of clay, algae and other small particles into bigger aggregates. Iron and sulfur bacterial slime is a widespread problem. Iron-precipitating bacteria are nourished by the dissolved ferrous iron in irrigation water. These bacteria stick to the surface of suspended soil particles and oxidize the dissolved iron. The oxidized iron precipitates as insoluble ferric iron. In this process, a slime called ochre is created and stick with other substances in pipelines to clog the emitters. Specific bacteria that oxidizes hydrogen sulfide and convert it into insoluble elemental sulfur, creates sulfur slime, a white or yellow stringy deposit formed by oxidation of hydrogen sulfide that is present mainly in shallow wells. The slime clogs emitters either directly, or by acting as an adhesive agent for other small particles. 8.4. Chemical Precipitates Chemical clogging of emitters frequently results from precipitation of one or more of the following cations: calcium, magnesium, iron and manganese. These materials may precipitate from the solution and form scales that partially or fully clog emitters. Precipitation can be triggered by changes in pH, temperature, pressure, water flow velocity and reaction with ions that are injected into the irrigation water by fertigation as well as by exposure to atmospheric oxygen. Table 8.1. Relative Clogging Potential of Micro-emitters by Water Contaminants Water characteristic Minor Moderate Severe pH <7.0 7.0-8.0 >8.0 TDS (Total dissolved solids) - ppm <500 500-2000 >2000 Suspended solids - ppm <50 50 -100 >100 Manganese - ppm <0.1 0.1-1.5 >1.5 Iron - ppm <0.2 0.2-1.5 >1.5 Hydrogen sulfide - ppm <0.2 0.2-2.0 >2.0 Bacteria population - per ml <10,000 10,000-50,000 >50,000 After Blaine Hanson. 1997 8.5. Water Hardness Water containing substantial concentrations of Ca++ , Mg++ and Fe++ is regarded as “hard water”. Hard water can precipitate poorly-soluble carbonates in the irrigation system. Water “hardness” is expressed as a calcium carbonate concentration equivalent in mg/l units. Hardness is calculated by measuring the content of the above mentioned Cations, summing up their concentrations expressed in meq/l and multiplying by 50 (the equivalent weight of calcium carbonate). Example: Calcium equivalent weight ≈ 20 Calcium concentration in the water: 120 mg/l ≈ 120/20 = 6 meq/l Magnesium equivalent weight ≈ 12 Magnesium concentration in the water 60 mg/l ≈ 60/12 = 5 meq/l Total 11 meq/l
- 94. SPRINKLER IRRIGATION 73 Water hardness= 11 meq/l X 50 = 550 mg/l Calcium Carbonate Equivalent The most prevalent precipitate from hard water is calcium carbonate. However when fertigating with fertilizers that contain phosphorous and sulfur, calcium phosphate and calcium sulfate (gypsum) may also precipitate. Similar reactions precipitate magnesium bi-carbonate. 8.5.1. Iron and Manganese in Water Iron is often dissolved in groundwater as ferrous bi-carbonate. When exposed to air, or to activity of iron bacteria, the iron is oxidized, precipitates and can plug micro- emitters. Manganese is occasionally present in irrigation water, but at lower concentrations and with lower activity as a clogging factor than iron. 8.6. Biochemical Oxygen Demand (BOD) Organic matter suspended in the water is decomposed by microorganisms that consume oxygen along the process. The quantity of oxygen consumed by these organisms in breaking down the organic matter is designated as the Biochemical Oxygen Demand or BOD. BOD is a consistent indicator for clogging hazard of micro- emitters by suspended organic matter. Raw sewage and low-quality reclaimed water have high levels of contamination and consequently high BOD values. 8.7. Filtration Because of the narrow water passageways in micro- emitters and the slow water-flow velocity, micro irrigation systems are susceptible to clogging much more than conventional sprinklers. As mentioned before, prevention of clogging necessitates high-level filtration and complimentary chemical and physical water treatments. 8.7.1 Screen (Strainer) Filters Screen filters' features are defined by filtration degree, filtration surface area and filtration ratio. 8.7.1.1. Filtration degree is designated in microns or mesh number. The filtration degree in microns indicates the diameter of the biggest ball-shaped particle that can pass between the screen wires. 8.7.1.2. Mesh number counts the number of wires along a 1" (25.4 mm) length of the screen. The two concepts are not fully inter-convertible. Perforation width may differ between two screens with the same mesh number due to different wire thickness. Approximate conversion from one indication mode to another is done by rule of thumb: mesh number x microns ≈ 15,000. Example: Screen perforation 120 Mesh. What is the filtration degree in microns? 15,000/120 = 125 micron Fig. 8.1. Screen Filter From Netafim Brochure
- 95. SPRINKLER IRRIGATION 74 When selectingthe filtration degree, the dimensions of the water passageways in the emitter and the character of water impurities should be considered. When the impurities are suspended inorganic solids (sand, silt, chemical precipitates), the maximum perforation diameter should be 25%-30% of the sprinkler's nozzle or the micro-emitter's water passageway diameters. When the impurities are organic and biological materials, the maximum perforation diameter should not exceed 10%-20% of the water passageway diameter in the emitters. Screen filters are most suitable for water with inorganic impurities, while high loads of organic and biological impurities commit other types of filters since the impurities may quickly clog the screen. There is wide selection of screens. In selecting screen type, water quality and emitter water passageway structure have to be considered. Perforated steel screen is the strongest structure but its effective filtration ratio is the lowest. It is used mostly in filters that are installed to protect the pumping unit when the pumped water contains coarse soil particles, gravel and stones. Woven wire is the most prevalent type of screen. Its effective filtration ratio is the highest, but the structure is the least robust. Wedge wire strength is intermediate and it is only rarely used. One of the main disadvantages of screen filters is the fast accumulation of dirt on the screen's surface. The accumulated dirt increases the head losses and may trigger collapse of the screen. Monitoring the pressure difference between the filter inlet and outlet is necessary to scrutinize excessive dirt accumulation on the screen. The filter has to be flushed and cleaned when the pressure difference between inlet and outlet approaches 5 m. (0.5 bar). Table 8.2. Screen Perforation Examples Mesh No. Hole size – microns Wire thickness - microns 40 420 250 50 300 188 80 177 119 100 149 105 120 125 86 155 100 66 200 74 53 Perforated Steel Wedge Wire Woven Wire Fig. 8.2. Screen Patterns
- 96. SPRINKLER IRRIGATION 75 Fig. 8.3.Head Losses in Clean Screen Filters Adapted from "Odis" brochure 8.7.2. Disc Filters Disc filters are suitable for filtration of water containing mixed, inorganic and organic impurities. The casing is made of metallic or plastic materials. The filtering element is a stack of grooved plastic rings, tightened firmly by a screw on cap or by a spring that is compressed by a water-piston. Water is filtered as it flows from the perimeter into the stack inner space through the grooves. The intersections of the grooves provide in-depth filtering. Coarse particles are trapped on the external surface of the stack. Finer particles and organic debris stick to the inner grooves. Disc filters have a higher dirt-retention capacity than screen filters. The definition of the filtration degree is identical to that of screen filters and is usually indicated by the color of the discs. Fig. 8.4. Disc Filter 8.7.3. Media Filters Media filters protect emitters when using water with a high organic load from open water bodies or reclaimed water. Wide-body (0.5 - 1.25 m in diameter) media containers are made of epoxy-coated carbon steel, stainless steel or fiberglass.
- 97. SPRINKLER IRRIGATION 76 Fig. 8.5.Media Filters The filtering media are of 1.5 - 4 mm size mm basalt, gravel, crushed granite particles or fine silica sand of 0.3 – 1.5 mm effective size. The organic impurities adhere to the surface of the media particles. The accumulated dirt should be back-flushed routinely in order to eliminate excessive head losses. The filtration degree is defined equivalently to that of screen and disc filters. 8.7.4. Sand Separators High loads of sand and other solid particles should be removed before getting to the main filtration system. There are two methods of sand separation. The traditional practice was based on sedimentation of solid particles by slowing- down water flow in closed settling tanks or open basins. Closed tanks conserve the water Table 8.3. Sand Particle Size and Mesh Equivalent Sand No. Effective sand size – mm Mesh equivalent range Crushed Silica 12 1.1. – 1.2 80 - 130 Standard Sand 6/20 0.9 – 1.0 100 - 140 Crushed Silica 16 0.6 – 0.7 155 - 200 U.S. Silica 80 0.6 – 0.7 160 - 200 Crushed Silica 20 0.28 170 - 230 Fig. 8.6 Sand Separator - Working Pattern
- 98. SPRINKLER IRRIGATION 77 pressure whilethe use of open settling basins requires re-pumping of the treated water into the irrigation system. Centrifugal (vortex) sand separators deposit sand and other suspended particles heavier than water by means of the centrifugal force created by tangential flow of water into a conical container. The sand particles thrown against the container walls by the centrifugal force settle down and accumulate in a collecting chamber at the bottom. The collector is washed out manually or automatically. Clean water exits through an outlet at the top of the separator. Each separator has an optimal flow-rate range in which the most of the suspended particles are removed without excessive head-losses. At lower flow-rates, more sand remains suspended in the water. Fig. 8.7. Hydro-cyclone Sand Separator – Head-losses and Optimal Flow-rates From "Odis" brochure 8.7.5. Filter Characteristics 8.7.5.1. Reliability Disc filters' reliability is higher than that of screen filters. Collapse of the filtration element is uncommon. In screen filters, the screens are prone to be ripped due to corrosion and to collapse by pressure surges. The screen-supporting frame has to withstand these pressure surges. 8.7.5.2. Capacity and Head-losses Water loses pressure as it flows through a filter. The extent of head-losses depends on the filter design, filtering degree, flow-rate and the level of dirt accumulation. Normally, for a specific filter type and size, the finer the filtration degree, the lower the nominal discharge. This is due to faster dirt accumulation and higher head-losses. 8.7.5.3. Key Screen Filter's Attributes 8.7.5.3.1. Diameter: Designates the diameter of the water inlet and outlet. 8.7.5.3.2. Filtration Area: The total surface area of the filtration element. The required filtration area for moderately dirty water is 10 - 30 cm2 for each 1 m3 /h of flow-rate for sprinkler irrigation and 25 - 60 cm2 for micro-emitters 8.7.5.3.3. Perforation Area: The total open area of perforations.
- 99. SPRINKLER IRRIGATION 78 8.7.5.3.4. EffectiveFiltration Ratio: The ratio between the perforation area and the filtration area. 8.7.5.3.5. Filter Ratio: The ratio between the perforation area and the inlet cross- section area. The higher the above mentioned parameters, the higher the filter capacity. The nominal capacity of other types of filters is defined according to the permissible head- losses. Table 8.4. Nominal Filter Capacity – Examples Make Filter type & diameter Filtration grade - microns Capacity m3/h Odis 2” screen 60-400 15-25 Arkal 2” disc 100-400 25 Arkal 2” disc 75 16 Arkal 2” disc 25 8 Amiad 3” screen 80-300 50 Amiad 3” disc 100-250 50 Odis 4” screen 60-400 80 Netafim 4” gravel 60-200 60-120 Netafim 6” sand separator 140-230 Nominal filter capacity designates the flow-rate at a head loss of 2 m (0.2 bars) in a clean filter. As dirt accumulates, the head loss increases. Filter cleaning is required when the head-loss amounts to 5 m. (0.5 bars). As mentioned before, a minimal- head-loss of 1.5 m (0.15 bar) is required for acceptable sand separation by hydro- cyclone sand separators but the recommended head-loss range in these separators is 2.5 - 5 m (0.25 - 0.5 bar). Dirt accumulation capacity is the lowest in screen filters, higher in disc filters and the highest in media (sand and gravel) filters. 8.7.6. Flow Direction The direction of the water flow through the filtration element is an important feature. In disc filters, water flows from the perimeter inwards. This pattern exposes to the flowing water the greater external surface area of the disc stack that is able to retain a much greater quantity of coarse particles than the smaller inner surface area. In screen filters, flow from inside outside is more suitable for self-cleaning mechanisms and is less vulnerable to screen collapse by pressure surges. Some models of screen filters have two filtering elements: an external preliminary coarse strainer that traps the coarse particles, and an internal finer screen for final filtration. In these Filters, flow direction is from the perimeter inwards. Some filter designs include nozzles in the inlet to induce tangential flow of water that drives the dirt to the distal end of the filter where it is flushed-out intermittently or trickles out continuously. In media filters, water enters from the top and exits from the bottom after crossing the filtering media that lies on a perforated plate. Back-flushing is accomplished in the opposite direction – from the bottom upwards. To facilitate proper back-flushing, the media fills no more than 2/3 of the tank volume, so that it can be lifted and agitated during the back-flushing process.
- 100. SPRINKLER IRRIGATION 79 8.7.7. FilterCleaning As mentioned before, filters have to be cleaned routinely before contaminants accumulation causes excess head losses or may cause collapse of the filtration element. Filters can be cleaned manually or automatically. 8.7.7.1. Manual Cleaning Conventional screen filters have to be disassembled. Each component has to be flushed. The integration of the screen and its supporting frame has to be checked. Torn screens have to be replaced. Some screen filters are equipped with mechanism that enables manual cleaning without disassembling the filter. a. Disassembled Screen Filter b. Rotating Brushes (BrushAway) c. Rotating Suction Nozzles (ScanAway) Fig. 8.8. Manual Cleaning of Screen filters From Netafim and Amiad Brochures In disc filters, the discs, that are fastened in the stack have to be relieved and separated from each other, prior to flushing. The best way of cleaning conventional disc filters is to flush the stack with water from a hose, after the release of its fastening knob. The separation of the discs by the water flow enables the removal of the impurities from the discs' grooves. 8.7.7.2. Automatic Flushing and Cleaning Diverse automatic cleaning mechanisms have been developed. The cleaning process is either continuous or pulsated. Continuously self-flushing screen filters maintain a flow of filtered water without the build-up of head losses. The dirt is continuously removed from the screen by a Fig. 8.9. Manual Hose Flushing of a Disc-filter Fig. 8.10. Continuous Flushed Circulating- filter
- 101. SPRINKLER IRRIGATION 80 tangential, spiralingdownward water flow, which flushes the debris into a collecting chamber at the bottom of the casing. The accumulated dirt is drained manually, constantly by a bleeder, or is automatically released when a preset water differential between the water inlet and outlet had been built. In most of them the pressure differential is monitored and the self-cleaning process is activated when the preset pressure differential had built-up. The intervals between flushing events may be also controlled by a timer. a. High-capacity Automatic Filter b. Compact Automatic Filter Fig. 8.11. Automatic Screen Filters with Scanning Nozzles The cleaning process is carried on for a preset time length. The cleaning and flushing mechanism is powered by the inherent pressure of the system or by an electric motor. Rotating brushes or sucking nipples clean the screen. For coarse screens, of over 200-micron filtering degree, brushes are sufficiently efficient while for finer screens under 200 microns, cleaning by rotating suckers is more effective. Fig. 8.12. Automatic Flushing of Disc-filter Adapted from "Arkal" brochure Automatic flushing of disc filters requires the release of the discs in the stack. The Spin-Kleen mechanism combines release of the stack tightening-screw, back- flushing by water counter-flow, and spinning of the relieved discs by the water stream that flushes the dirt from the grooves to a draining valve that opens automatically.
- 102. SPRINKLER IRRIGATION 81 Media filtersare flushed automatically by backflow from the bottom that floats the accumulated dirt and releases it out through the drain valve on top. The reverse-flow is activated automatically when the preset pressure differential has been reached. Automatic flushing of media and disc filters requires counter-flow of filtered water. To meet this requirement, filters operate in arrays and the flushing of filters is sequential, one after another. Fig. 8.13. High-capacity Media-filter Array Fig. 8.14. Back-flushing of Media-filters 8.7.8. Filter Location Sand settling tanks are installed ahead of the pump while sand separators are installed just downstream of the pump. In highly contaminated water, multi-stage filtration is required. An automatic screen, disc, media filter or a filtration array of several filters should be installed at the pumping site or the main control head. Backup control screen or disc filters should be installed at the head of each irrigating sector. With moderately contaminated well water, one filtration stage at each zonal valve may be sufficient. 8.8. Supplementary Water Treatments With micro-emitters, in addition to filtration, complementary chemical treatments should be performed on the irrigation water to prevent the clogging of the emitters. Oxidation and acidification are the prevalent complementary treatments. Oxidation decomposes organic matter, prevents formation of slime by sulfur and iron bacteria, blocks development of algae and eliminates infestation by pathogens. Acidification eliminates chemical precipitation and dissolves in-built precipitates in the irrigation system. 8.8.1. Chlorination Chlorine, the common oxidizing agent appears in three forms: a. Solid tablets containing 90% chlorine. b. Liquid sodium hypochlorite (NaOCI) containing 10% chlorine. c. Gaseous chlorine. This form is cheap and efficient but is unsafe in use and commits strict pre-caution measures in application.
- 103. SPRINKLER IRRIGATION 82 When ferrousiron is present in the water, one ppm (part per million) of chlorine is required per each ppm of iron to kill iron bacteria and precipitate the iron from the water. When hydrogen sulfide is present, 9 ppm of chlorine are needed per each ppm of sulfur to kill the sulfur bacteria, prevent slime growth and precipitate the sulfur from the water. The precipitates formed in theses processes, must be retained by the control filters at the zonal irrigation control heads to prevent clogging of the emitters. Effective chlorinating decomposes organic materials and blocks the development of algae and plankton in the laterals and the emitters. 1 - 2 ppm of residual chlorine detected at the distal ends of the laterals indicates adequate chlorination. To maintain these residual levels, chlorine concentration in the water at the injection point should range between 3 – 15 ppm, depending on the impurity load and duration of injection. Levels higher than 15 ppm can harm the diaphragms in certain hydraulic valves. 8.8.2. Acidification Acidification of water is required when "hard" water containing high concentrations of bi-carbonates is used for irrigation with micro-emitters. The injected acid neutralizes the transient hardness and immerse calcium carbonate precipitates. Acid can be applied with ordinary fertigation equipment or by a dedicated metering pump. The common acidifying agents are sulfuric, nitric, hydrocloric and phosphoric acids. Chlorination of acidified water is more effective than chlorination of alkaline water, reducing the chlorine requirement. Hence if both chlorination and acidification are done simultaneously, acidification will be applied first, followed by chlorination. Mixing acid with chlorinating agents is forbidden since it can induce a toxic chemical reaction. Commonly, chemical treatments are implemented upstream from the filtration system. The impurity load is reduced and the decomposed material is trapped in the filters. The narrower the water passages in the emitters, the greater the need for chemical treatments. That rule is excluded when, as mentioned before, the oxidation of iron and sulfur bacteria forms solid particles that have to be retained by control filters in the irrigation zonal heads.
- 104. SPRINKLER IRRIGATION 83 9. FERTIGATION 9.1.Introduction Fertigation is the technology of applying nutrition elements via the irrigation water by injection of fertilizer solutions into the irrigation system. Contemporary fertigation technology emerged at the sixties of the 20th century, following the introduction of commercial drip irrigation. Prior to that era, direct application of nutrition elements to the water had been implemented only in hydroponics growing systems. Later it was realized that crops benefit of fertigation in all the pressurized irrigation technologies and in some circumstances, although rarely, in surface irrigation too. The combined application of water and fertilizers through the irrigation system increases the efficiency of fertilizer utilization, raises yields, improves produce quality and minimizes environmental pollution caused by excess fertilization. 9.1.1 Advantages of Fertigation a. Improved efficiency 1. Uniform distribution with irrigation water 2. Better synchronization with crop demands i. Adjustment of amounts and ratio between nutrients along the growing season 3. Deeper penetration of the nutrients into the soil 4. Avoiding nutrient losses from soil surface b. Avoiding soil compaction by fertilizer spreaders c. Avoiding damage to canopy and yield d. Reduction of fertilizer losses e. Additional functionality 1. Application of herbicides and pesticides via the irrigation water 9.1.2. Limitations and Risks in Fertigation a. Hazard of backflow of nutrient solution into the drinking water supply network b. Only fully soluble fertilizers are applicable c. Hazard of corrosion, precipitate-formation and clogging in the irrigation system d. Use of dangerous acids and inflammable materials e. Costly investment in accessories and storage installations f. Incorrect application may cause damage to crop, nutrient losses by leaching beneath the root-zone and contamination of underground water resources g. Hazard of foliage and fruit scorching in overhead irrigation h. Large storage volumes are needed for nutrient solutions 9.2. Technologies of Fertigation A variety of technologies have been developed for injecting fertilizers into the irrigation system. 9.2.1. Patterns of Injection 9.2.1.1. Fertilizer Concentration a. Decreasing along time (Fertilizer tank) b. Uniform – pulsating (piston and diaphragm pumps) c. Uniform – constant (venturi, internal mixing pumps, mixers)
- 105. SPRINKLER IRRIGATION 84 9.2.1.2. EnergySources a. Inherent pressure of the irrigation system b. External energy sources 1. Electricity 2. Internal combustion engines 9.2.1.3. Injector Types a. Pressure differential b. Venturi (suction) c. Fertilization pumps 9.2.2. Fertilizer-tank Throttling the water flow in the control head creates pressure differential that diverts a fraction of the irrigation water through a tank containing the fertilizer solution. A gradient of at least 1 – 2 m. (0.1 – 0.2 bars) is required to redirect an adequate stream of water through a connecting tube of 9 – 12 mm diameter. The tank, made of corrosion-resistant enamel- coated or galvanized cast iron, stainless steel or fiberglass, has to withstand the irrigation network working pressure. The diverted water is mixed with solid soluble or liquid fertilizers. When solid fertilizers are used, the nutrient concentration remains more or less constant, as long as a portion of the solid fertilizer remains in the tank. Once the solid fertilizer had been fully dissolved, continuous dilution by water gradually decreases the concentration of the injected solution. 9.2.2.1. Fertilization-tank Advantages a. Simple construction and operation b. Low cost (of small units) c. Extensive field experience d. No need of external energy source e. Good mobility f. Wide dilution ratio 9.2.2.2. Fertilization-tank Limitations a. Head losses by throttling b. High cost of large units c. Non-uniform nutrient concentration along the period of application d. Fertilizer replenishment is needed prior to each application e. Integration with automation is problematic Fig. 9.1. Fertilizer-tank From "Odis" brochure
- 106. SPRINKLER IRRIGATION 85 f. Thetank and the accessories have to withstand the mainline operating pressure 9.2.3. Venturi Injector Suction of the fertilizer solution is created by water flow through a constricted passageway. The high flow velocity of water in the constriction reduces water pressure below the atmospheric pressure so that fertilizer solution is sucked from an open tank into the constriction through a small diameter tube. Venturi devices are made of corrosion-resistant substances such as copper, brass, stainless steel and plastic materials. The injection rate depends upon the pressure loss, which ranges from 10% to 75% of the irrigation system's pressure and is determined by the injector type and operating conditions. Venturi devices require extra pressure to allow for the necessary pressure-loss. Maintaining a constant pressure in the irrigation system guarantees uniform nutrient concentration in the irrigation water along the application period. The customary head-losses are above 33% of the inlet pressure. Double-stage Venturi injectors have lower pressure-losses downward to 10%. The suction-rate depends on the inlet pressure, pressure-loss and the diameter of the suction tube. It can be adjusted by valves and regulators. Suction- rates vary from 0.1 l/h to 2000 l/h. Venturi injectors are installed in-line or on a by- pass. In greenhouses, the water flow in the bypass may be boosted by an auxiliary pump. 9.2.3.1. Venturi Suction Injector Advantages a. Simple to operate, easy to install, no moving parts b. Wide-range of flow-rates (in different models) c. Low cost of small devices, The solution is sucked from an open tank d. Good mobility e. Constant suction-rate (in constant pressure regime) f. Easy integration in automation g. Cheap, open to the atmosphere tanks may be used h. Corrosion resistance 9.2.3.2. Venturi Suction Injector Limitations a. High head-losses b. Sensitivity to pressure fluctuations c. Narrow discharge-range of each model 9.2.4. Injection Pumps Fertilizer pumps are driven by electricity, internal combustion engines, tractor PTO or hydraulically by the inherent water pressure in the irrigation system. Fig. 9.2. Venturi Injector Courtesy "Netafim" Fig. 9.3. By-pass Venturi Installation Courtesy "Netafim"
- 107. SPRINKLER IRRIGATION 86 9.2.4.1. PumpInjectors Advantages a. Uniform nutrient concentration along the fertigation process b. Easy control of amount and concentration of the nutrient solution c. Convenient integration with automation d. No pressure losses 9.2.4.2. Pump Injectors Limitations a. High initial cost b. Complicated operation c. Wear of moving components d. Suitable only with fertilizer solutions e. Some models need external power source f. Some models emit surplus driving-water outside 9.2.4.3. Hydraulic Pumps Versatile devices, reliable and feature low operation and maintenance costs. A diaphragm or piston movement injects the fertilizer solution into the irrigation system. Water-driven diaphragm and piston pumps combine precision, reliability and low maintenance costs. 9.2.4.3.1. Hydraulic Pump Types a. Piston pumps b. Diaphragm pumps c. Internal-mixer pumps Fig. 9.4. Piston (left) and Diaphragm (right) Hydraulic Pumps From "Amiad" Brochure Fig. 9.5. No-drain Internal-mixer Hydraulic Pump From "Dosatron" brochure
- 108. SPRINKLER IRRIGATION 87 Fig. 9.6.Piston Pump Installation on Control-head 9.2.4.3.2. Injection Control Hydraulic pumps used in fertigation can be automated. A pulse transmitter is mounted on the pump. The movement of the piston or the diaphragm's spoke sends electrical signals to the controller that measures the delivered volume. Measurement can also be performed by small fertilizer-meters installed on the injection tube. Fertilizer-meter is a modified water-meter, corrosion resistant and precise in measurement of small solution quantities. The controller allocates fertilizer solution according to a preset program. In glasshouses, simultaneous application of a multi-nutrient solution is routine. When the distinct chemical compounds in the fertilizers are incompatible and cannot be combined in a concentrated solution due to the risk of decomposition or precipitation, Two or three injectors are installed in- line one after another, in the control- head. The application ratio between the injectors is coordinated by the irrigation controller. In high-income crops grown in glasshouses on detached media, the irrigation water is mixed with fertilizers in a mixing chamber (mixer). 9.2.4.3.3. Centrifugal Pumps Centrifugal pumps are used when high capacity is needed or the fertilizer Fig. 9.7. Fertilizer Solution Meter with Pulse Transmitter From "Arad" Brochure Fig. 9.8. Mixer Array From "Odis" brochure
- 109. SPRINKLER IRRIGATION 88 solution isturbid. 9.2.4.3.4. Roller Pumps Roller pumps are used for precise injection of small amounts of a nutrient solution. Their life-span is relatively short due to bearings' corrosion by the injected chemicals. 9.2.4.4. Electric Pumps 9.2.4.4.1 Electric Pumps Advantages a. Precise and reliable b. Suitable for extremely low dosage c. Conveniently integrated with automation d. Wide range of flow-rates 9.2.4.4.2. Electric Pumps Limitations a. Need of external energy source b. Fails in blackout occasions Electric pumps are inexpensive and reliable. Operation costs are low and they are readily integrated into automatic systems. A wide selection of pumps is available, from small low-capacity to massive high-capacity pumps. The working pressure is 10 - 100 m. (1 – 10 bars). Electric piston pumps are exceptionally precise and suitable for accurate mixing in constant proportions of a number of stock solutions. Variable speed motors and variable stroke length allow for a wide range of dosing from 0.5 to 300 L/h. 9.3. Injection Site Options: 9.3.1. Injection at the Main Control-head - the most convenient and cost- effective alternative. 9.3.2. Injection at Sub-main Heads - a common practice in field crops. 9.3.3. Injection at the Control-head of Each Block – more expensive than the above-mentioned alternatives. 9.4. Control and Automation Dosing patterns: 9.4.1. Quantitative Dosing: a preset amount of fertilizer is injected into the irrigation system during each water application. Injection may be initiated and controlled automatically or manually. 9.4.2. Proportional Dosing: maintains a constant predetermined ratio between the irrigation water and the fertilizer solution. Pumps inject the fertilizer solution in a pulsating pattern. Venturi injectors apply the fertilizers continuously and in constant concentration. Fig. 9.9. Electric Pump
- 110. SPRINKLER IRRIGATION 89 9.5. AvoidingCorrosion Damage Most fertilizer solutions are corrosive. Accessories exposed to the injected solution should be corrosion-resistant. The injection device and irrigation system must be thoroughly flushed after fertilizer injection. 9.6. Back-flow Prevention Whenever the irrigation system is connected to a potable water supply network, strict precautions should be taken to avoid backflow of fertilizer-containing irrigation water. 9.6.1. Back-siphonage occurs when low pressure in the supply line is created by an excessive hydraulic gradient in undersized pipes in the supply line, a break in the supply line, pump or power failures. 9.6.2. Back-pressure occurs when the pressure in the irrigation system is higher than in the water supply network. This happens when booster pumps are used for pressure increase in the irrigating area or when the irrigated area is topographically higher than the local water supply tank. An atmospheric vacuum breaker can be installed beyond the last valve to allow air entry downstream when pressure falls. A pressure vacuum breaker has an atmospheric vent valve that is internally loaded by a spring. This valve is unsuitable for fertigation systems operated by an external source of energy. Vacuum breakers are effective only against back-siphonage and do not prevent back-pressure. A dual check valve assembly has two check valves in tandem, loaded by a spring or weight. The device is installed upstream from the injection system and is effective against backflow caused by both back-pressure and back-siphonage. A reduced pressure backflow preventer is also consisted of two internally loaded check valves separated by a reduced pressure zone. When pressure downstream is higher than the pressure upstream, water is released to the atmosphere and does not flow backwards. 9.7. Chemical Aspects of Fertigation a. Interaction between fertilizers and irrigation water b. Interactions between fertilizers 1. Precipitation 2. Decomposition 3. Antagonism 4. Synergism Diverse interrelations prevail between chemical agents immersed simultaneously in water. When fertilizer solution is injected into the irrigation water, the cations and anions that compose the fertilizer react with the cations and anions inherent in the water. Some Fig. 9.10. Tandem Back-flow Preventer
- 111. SPRINKLER IRRIGATION 90 reactions maycreate insoluble compounds that precipitate and may clog filters and emitters. That mostly happens with phosphoric fertilizers injected into calcium and magnesium rich water (hard water) of high pH level. Chelates of iron and manganese may decompose when mixed with acid fertilizers. Other patterns of interrelations are antagonism and synergism between ions. Generally, ions of the same type of electrical charge (+ or -) are antagonistic to each other and compete in absorption and bio-reactions in the plant. For example: high level of potassium induces magnesium deficiency and vis versa. Between ions with different sign may exist synergism – positive impact on each other. For example, simultaneous presence of potassium and nitrate in solution increases absorption of both ions. The chemical aspects have to be considered when nutrient application with fertigation is scheduled. 9.8. Safety Many fertilizers are corrosive. Some of them may be toxic, carcinogenic or inflammable. Dealing with fertilizers commits caution measures. a. When dealing with fertilizers, one has to wear protective clothes and to use goggles, gloves and boots. b. When diluting acids, the acid has to be poured slowly into a great amount of water, to avoid heating and boiling of the solution. Water will be never poured into the acid. c. Some of the fertilizers are inflammable. No weeds and garbage are allowed in the injection site and storage vicinity. Table 9.1. Electric Charges of Nutrients CATIONS ANIONS Ammonium NH4 + Nitrate NO3 - Potassium K+ Phosphate H2PO4 - Calcium Ca++ HPO4 = Magnesium Mg++ Sulfate SO4 = Iron Fe++ Molibdate MoO4 = Fe+++ Borate B4O7 = Zinc Zn++ Manganese Mn++ Copper Cu++ Sodium Na+ Chloride Cl-
- 112. 91 S P RINK LE R I R R I G A T I O N 10. FLOW-RATE – WATER HEAD RELATIONSHIP 10.1. Water Head In pressurized irrigation systems, water exists under pressure. The water pressure is a key factor in these systems' performance. For sake of convenience in calculation, the term head, is preferred in dealing with pressure in irrigation systems. Water head is actually the potential (or the free energy) that the water retains to accomplish work. The work done is mostly the delivery of water from one point to another through the irrigation network. The water potential is related to a reference point. By definition, the reference point is the atmospheric pressure at sea level at standard ambient temperature (250 C). Pressure can be expressed in different unit systems. As mentioned before, for simplicity and convenience in irrigation systems design, the preferred unit system is the dynamic head, expressed in meters (m) height of water column. This unit system incorporates the effects of topography and friction losses in pipes on the dynamic head, at each point of the irrigation system. Water dynamic head can be referred to as the hydraulic potential energy of the water. Water flowing in pipes loses energy by friction with pipe walls and other components of the irrigation system. The friction losses can be classified in two categories: a. Longitudinal Friction Losses (hf): arise from the friction of the water with the pipe walls. The losses accumulate along the pipe. b. Local Losses (ht): are created by the turbulence that occurs by sudden changes in the flow pattern, as in abrupt change in pipe diameter, the flow through a valve or a filter, bends in the pipeline, etc. These losses are local but have to be taken into account and added to the longitudinal losses. The total water head, measured at a specific point of the irrigation system, is composed of three ingredients: 10.1.1. Elevation Head (z) Elevation head is derived from the topographic position, the relative height of a given point above or below a point of reference. For example, if the main valve in the plot is positioned 5 m above the distal end of the plot, the measured static (elevation) head at the distal end will be 5 m higher than the static head measured at that valve. Static head is the pressure measured at a point in the water system when no water flow is taking place. Table 10.1. Pressure and Water Potential Units DEFINITION UNIT SUB-UNITS CONVERSION Pressure / water potential Bar =100 Centibars 0.99 Atm. Pressure / water potential Atmosphere (Atm) ≈100 Centibars 1.01 Bar Pressure / water potential Kilopascal (kPa) = 1000 Pascal 0.01 Bar=1 Centibar Head Meter =100 cm 0.1 Atm. ~ 0.1 Bar Pressure / water potential PSI ≈0.068 Atm. ≈0.68 m
- 113. 92 S P RINK LE R I R R I G A T I O N 10.1.2. Dynamic Head The dynamic head is the head measured in a certain point in the irrigation system, when water flow. The requested total dynamic head is the sum of the operating pressure, the friction head losses within the irrigation system and the pumping lift, if applicable. In a properly designed irrigation system, the total dynamic head should be the same in each concurrently irrigating subunit to ensure uniform water distribution in the irrigated sub-plots. 10.1.3. Velocity Head Flowing water has kinetic energy (velocity head) represented by V2 /2g where V is the velocity expressed in m/sec and g is the gravitational constant 9.81 m/sec2 . The velocity head can be expressed in m. units. Squaring V by itself (V x V = V2 ) results in units of m2 /sec2 which divided by g in m /sec2 units, expresses velocity head in the same units as dynamic head, namely the height of water column in m. units. 10.2. Head Losses As mentioned before, head-losses result from friction between the pipe walls and water as it flows through the system. Obstacles - turns, bends, expansions and contractions, etc., along the water flow route, increase head losses. The extent of head losses is a function of the following variables: a. Pipe length b. Pipe diameter c. Pipe wall smoothness d. Water flow-rate (discharge) e. Water viscosity 10.2.1 Friction Losses As mentioned before, there are two types of friction losses: Major (longitudinal) losses: losses in water flow along straight pipes. Minor (local) losses: are created by the flow at bends and transitions in different accessories. If the flow velocities are high through many bends and transitions in the system, the minor losses can build-up and become substantial losses. 10.2.1.1. Longitudinal Friction Losses The calculation of friction head losses in pipes is based on the following data: a. The friction coefficient (for convenience - C) of the pipe, which is a constant value for a specific pipe and depends on the smoothness or roughness of the inner surface of the pipe wall. b. The internal pipe diameter d, the greater the diameter, the smaller the friction losses in a given flow-rate. c. Flow-rate Q, the greater the flow-rate, the greater the friction losses. d. Pipe length L, the greater the length, the greater the friction losses. The common equation used to calculate friction losses of water flow along a pipe is known as the Hazen-Williams equation.
- 114. 93 S P RINK LE R I R R I G A T I O N 8748521 ..12 D) C Q (101.131=‰)J( − ××× (Eq. 10.1) Where: J (‰) = head-loss (m. per 1000 m. length) Q = flow-rate (m3/h). C = friction coefficient (indicates inner pipe wall smoothness, the higher the C coefficient, the lower the head losses). D = inner pipe diameter (mm) The Hazen-Williams equation is valid in a narrow range of temperatures and flow patterns. The friction coefficient C that depends on the smoothness of the internal pipe wall may decrease along time, due to corrosion in non-coated steel pipes and accumulation of precipitates in all types of pipes. In small diameter laterals, the Darcy-Weisbach equation gives more accurate results in calculating head losses. Most commonly it takes the following form: = gD LV fHf 2 2 (Eq.10.2) Where: Hf = Head-loss – m. f = Darcy-Weisbach friction factor L = Pipe length – m. V = Flow velocity – m/sec D = Inner pipe diameter – m. g = gravitational acceleration (9.81 m/sec2) Both the Hazen-Williams and Darcy-Weisbach equations include a parameter for the smoothness of the internal surface of the pipe wall. In Hazen-Williams, it is the dimension-less C coefficient and with Darcy-Weisbach the roughness factor f, expressed in mm. In Hazen-Williams equation, as the C coefficient is higher, head losses will be lower. On the opposite, in the Darcy-Weisbach equation, higher values of the friction factor f indicate higher head-losses. The head losses can be expressed graphically by the slope of the Piezometric line along the length of the flow path. In the category of friction losses, the Piezometric line declines Table 10.2. Friction Coefficients Pipe material f - mm (Darcy-Weisbach) C (Hazen-Williams) PVC and PE 0.0015 - 0.007 140-150 Asbestos-cement 0.3 130-140 New steel 0.045 – 0.09 110-120 5 year old steel 0.15 – 4.0 80-90 Steel with internal concrete coating 0.3 – 1.0 110-120 Concrete 0.3 – 5.0 90-100
- 115. 94 S P RINK LE R I R R I G A T I O N gradually and is depicted as a straight, sloping line, descending in the flow direction. An abrupt, vertical decline of the Piezometric line expresses local losses. There are no local losses at all in section (1) - (2) of the pipe shown in Fig. 10.1. The only head loss in this section is the friction loss. This loss is expressed by the incline of the Piezometric line along the section; the value of the loss hf equals the drop of the energy line in section (1)-(2). As there are no changes in the values of C, d and Q, the value of the friction loss per a length unit is constant and increases uniformly in the flow direction along the pipe. The friction loss per longitudinal unit (the hydraulic gradient) is commonly expressed by the letter J. Its value is calculated by: (Eq.10.3) From Fig. 10.1., it is explicit that J is indeed the incline of the Piezometric line. It is usually expressed in percentage (%), per-mil (0 /oo), or in the form of a decimal fraction. Example: if in Fig. 10.1 L = 100 m., E1 = 101.5 m., E2 = 100.0 m , Then: J is the hydraulic gradient and is absolutely independent of the slope of the pipe! 10.2.1.2. Minor (local) Head-losses Minor head-losses are expressed as an equivalent length factor that adds a virtual length of straight pipe of the accessory diameter to the length of the pipe under calculation. Specific cases of local pressure losses: 10.2.1.2.1. Emitter Connecting Tubes Disturbance to Water Flow in Lateral Some micro-emitters are connected to laterals by means of small diameter tubes with barbed or screwed protrusions. These protrusions disturb water flow in the lateral and induce increased head losses. The rate of disturbance to the flow is designated by the coefficient Kd. The range of Kd is 0 – 2.00 (and sometimes higher). As this value is higher, head-losses increase. The value of Kd depends on the size and nature of the protrusion and the inner cross section of the lateral. Fig. 10.1. Graphic Presentation of Friction Head Fig. 10.2. Feeding Micro-tube Connection
- 116. 95 S P RINK LE R I R R I G A T I O N 10.2.1.1.2. Head Losses in the Connecting Tubes Micro-sprinklers and micro-jets utilize occasionally small diameter micro tubes of 4 – 8 mm inner diameter for connection between the lateral and the emitter. The smaller cross-section may generate considerable head losses in relatively short tubes of 50 – 100 cm. Decrease of pressure below the requested operation pressure may distort the optimal distribution pattern of micro-sprinklers and micro-jets. To prevent excessive head losses, emitters with a flow-rate higher than 30 l/hour will be connected to the lateral with tubes having a minimum inner diameter of 6 mm. 10.2.1.1.3. Head-losses in Valves and Accessories As mentioned before, head losses in accessories are often designated as the losses in equivalent length of a virtual pipe having the same diameter as the accessory. Nomograms of head losses as a function of flow-rate appear in commercial brochures and manuals. Certain producers designate a flow factor to valves and similar accessories. This value indicates the flow-rate that creates head losses of 10 m. (1 bar) while flowing through the accessory. ( ) 50.v p Q K ∆ = (Eq. 10.4) Where: Kv – flow factor, m3 /hour flow-rate with head-loss of 1 bar Q – flow-rate, m3 /hour ∆p – pressure drop, bars Example: Kv = 50; What is the head loss when Q = 30 m3 /h Manipulation of Eq. 10.04: ∆p = (Q/Kv)2 ∆p = (30/50)2 = (0.6)2 = 0.36 bar = 3.6 m. 10.2.1.2. Total Dynamic Head (TDH) The total dynamic head that has to be created by the pump is the sum of the pumping suction lift (the difference between water surface height at the source, and pump height), the requested working pressure in the emitters, and friction losses within the irrigation system. The energy consumed per pumped unit of irrigation water depends on the total dynamic head output of the pump and its pumping efficiency. As mentioned above, the total dynamic head depends on: a. The vertical distance that the water is lifted b. The pressure required in the emitters' inlets c. The friction losses that are created by the water flow from the water source through the pipelines and accessories such as valves and filters. Fig. 10.3. Head-losses in Hydraulic Valves (example)
- 117. 96 S P RINK LE R I R R I G A T I O N As mentioned before, pumping system efficiency depends upon the pump maintenance level, its power unit effectiveness, and the efficiency of power transmission between them. The power input required by the pump is calculated with the formula below: η× × = 270 HQ N (Eq. 10.5) Where: N = required input - HP Q = pump discharge – m3 /h H = total dynamic head – m ηηηη = pump efficiency – expressed as a decimal fraction Example: Q = 200m3 ; H = 150 m; η = 0.75. N = 200 X 150/(270 X 0.75) = 148 HP When measuring pressure, it should be remembered that the pressure gauges are calibrated to read 0 (zero) at atmospheric pressure (about 1 bar). This is important in the operation of devices such as Venturi suction injectors. 10.3. Operating Pressure The operating pressure is the pressure required at the emitters to guarantee effective performance and uniform water distribution. The range of the appropriate operating pressure of the emitter is defined and published by the manufacturer in the operating manual. The type of emitter and its operating pressure have to be taken into account in irrigation system design and irrigation scheduling. The design of the distributing pipelines has to guarantee the appropriate operating pressure in the emitters. The term ‘working pressure’ (PN) refers to the maximal allowed pressure in a component of the irrigation system (pipe, filter, etc.) that will not result in damage to the element by excessive pressure. There are different procedures for calculation of head losses. In the past, slide rulers and nomograms were routinely used. Nowadays, most system designers use dedicated software and on-line calculators. Head-losses in distributing pipes with multiple outlets differ from head-losses in non- distributing pipes. When using m. (meters) as head units, head-loss values are expressed in % or ‰ of pipe length. The actual head-losses are obtained by multiplying the percentage/ per-mil value by the pipe length (in m. units). Christiansen friction factor (F) is used to calculate the head losses in pipes with multiple outlets such as distributing mains and sub-mains, manifolds and laterals. This factor accounts for the decrease in flow along the lateral and depends upon the number of outlets (N) and the exponent (m = 1.76) of the flow-rate (Q) in Hazen- Williams equation. The formula for calculating this factor is as follows: F = 1/(m+1) + 1/(2N) +((m-1)0.5 /(6N)2 ) (Eq. 10.6)
- 118. 97 S P RINK LE R I R R I G A T I O N For a lateral with more than 10 emitters, F ≈ 0.40 can be used regardless of the friction loss formula utilized. The head-loss due to friction in laterals is then determined by: Hf = F××××Hp (Eq. 10.7) Where: Hf is the head-loss due to friction in the lateral. Hp is the head-loss due to friction of the same flow-rate in a non- distributing pipe of the same diameter and length. As mentioned before, in laterals where connecting tubes are inserted, molded inside or nailed with the stem protruding into the inner cavity of the lateral, the protrusions disturb the water flow and increase the head losses. These additional head losses are designated by Kd – the disturbance coefficient. The values range from zero to 2.0 and higher. When these values are high, the disturbance to flow and the derived head losses are substantial and commits a shorter lateral length. 10.4. Hydraulic Characteristics of Emitters Pressure variations have a different effect on the flow-rate of various emitter types. The impact depends on design and construction. The relationship between the operating pressure and the flow-rate of the emitter is calculated via the following equation: Q = k××××Px (Eq. 10.8) Where: Q = emitter flow-rate – l/h k = emitter discharge coefficient – depends on the configuration of the water path in the emitter and the units of pressure and flow-rate. P = Pressure at the emitter's inlet – m. x = emitter discharge exponent The emitter exponent indicates the relationships between the pressure and the flow-rate of the emitter. The range of emitter exponents is 0 – 1. in most sprinklers the exponent is around 0.5. The larger the emitter exponent, the more sensitive is the flow-rate to pressure variations. A value of 1 means that for each percentage change in pressure there is an identical percentage change in flow-rate. An exponent value of 0 (zero) means that the emitter's flow-rate is not affected by pressure changes. That happens in compensating emitters above the regulating pressure threshold. Table 10.3. Multiple Outlets Factor F Number. of outlets F 1 1.00 5 0.410 10 0.384 20 0.373 40 0.368 100 0.366 Table 10.4. Effect of the Emitter Discharge Exponent on Pressure – Flow-rate Relationship Exponent 0.4 0.5 0.6 0.7 0.8 Pressure change - % Flow-rate change - % 10 3.9 4.8 5.9 6.9 7.9 20 7.6 9.5 11.6 13.6 15.7 30 11.1 14.0 17.1 20.2 23.3 40 14.4 18.3 22.3 26.6 30.9 50 17.6 22.5 27.5 32.8 38.3
- 119. 98 S P RINK LE R I R R I G A T I O N 10.5. Calculation of Head Losses As mentioned before, slide rulers, tables, nomograms, hand-held and on-line calculators as well as dedicated software can be used to calculate head losses. Manufacturers publish tables and nomograms showing the head losses in their products. Valve producers use the Kv Flow Factor that designates the discharge of the valve in m3 /h units at 10 m (1 bar) head loss. 10.6. Technical Data Sprinkler and micro-emitters manufacturers provide detailed technical data in catalogs or on-line, about the flow-rate - pressure relationships of their products. These data should be used for determining lateral length and the pressure required at the lateral inlet. In taking decisions, the convention of maximum allowed flow-rate difference below 10% between emitters in a simultaneously irrigated area has to be followed. Manufacturers provide tables indicating the acceptable lateral length in a plateau and selected slopes for a given emitter and lateral combination that keeps the head differences in the allowed range of ± 5% around the average flow-rate. 10.6.1. Pressure Measurement An adequate pressure regime in the irrigated area is a prerequisite for optimal irrigation. Each type of emitter has its allowed pressure range in which the water distribution is satisfactory. Deviation from the allowed range decreases the efficiency of water application. The pressure can be measured at fixed measuring points by mounted pressure gauges or by portable pressure gauges that are fitted to measure the pressure in the sprinkler nozzle. Another device is a portable pressure gauge, equipped with a needle that can be inserted into specific nipples that have been installed on specific accessories in the irrigation system like elbows, plugs, fertigation devices, etc. 10.6.2. Calculation of Longitudinal Head Losses The calculation of the predicted head losses is essential in the design of a new irrigation system. It is particularly important in the comparison of the actual performance of the irrigation system with the designed performance. The discharge of the emitter is related to the pressure according to the formula: (Eq. 10.9) When: Q = Emitter discharge, m3 /h P = Sprinkler pressure, bar. d = Nozzle nominal diameter, mm C = Coefficient dependent on the sprinkler structure. Its average value is 0.9. Fig. 10.4. Pressure Measurement
- 120. 99 S P RINK LE R I R R I G A T I O N Table 10.5. Head-losses in Non-distributing Aluminum Pipes, m. Head per 100 m. of Pipe Length (without Outlets) Discharge Nominal Diameter M3 /h 2” 3” 4” 6” 8” 2 0.32 0.02 3 0.71 0.09 0.01 4 1.24 0.16 0.03 6 1.89 0.23 0.05 8 3.54 0.44 0.09 10 5.69 0.72 0.17 15 13.32 1.66 0.39 0.03 20 20.95 2.62 0.63 0.07 0.01 30 49.50 6.07 1.40 0.19 0.04 35 63.00 7.82 1.82 0.23 0.05 40 9.70 2.28 0.30 0.06 45 11.71 2.78 0.37 0.08 50 14.39 3.36 0.44 0.10 55 17.02 3.94 0.51 0.12 60 21.18 4.90 0.60 0.15 80 34.50 8.05 1.06 0.26 90 44.60 10.42 1.36 0.33 100 12.90 1.68 0.40 120 19.31 2.58 0.58 150 29.90 3.89 0.92 180 5.02 1.20 200 6.23 1.50 250 9.18 2.19 300 14.60 3.48 350 18.90 4.51 400 5.11 425 6.14 450 6.85 The calculation of head-losses can be done with the Hazen-Williams formula. In daily life, tables, nomograms, specific slide-rules and computer software facilitate the determination of head losses. Example: L = 500 m., Q = 60 m3 /h, d = 6” It is found in the table above that at flow-rate of 60 m3 /h in 6” aluminum pipe, the head-loss is 0.6 m. per 100 m. length (0.6%). The head-loss in 500 m. length will be 0.6 X 500/100 = 3 m. 10.6.2.1. Head-losses in Laterals The results obtained from the tables and the nomograms relate to a blind pipe without outlets. Discharge of water from outlets along the pipe decreases the accumulating total head loss in the pipe, compared with a non-distributing pipe. In this case the calculation of the head losses along the pipe can be done incrementally between the outlets.
- 121. 100 S P RINK LE R I R R I G A T I O N A shortened procedure facilitates the calculation of the head losses in laterals by the multiplication of the head loss in blind pipes by the F coefficient. As mentioned before, the value of the F coefficient depends upon the number of outlets along the pipe and the distance of the first emitter from the entrance to the lateral. This procedure is valid if the discharge of each emitter and the intervals between the emitters along the lateral are equal. In table No. 10.6, (a more detailed version of table 10.3). the F coefficient in laterals is presented. X=1 indicates that the distance between the sub-main/manifold and the first emitter is equal to the intervals between the emitters along the lateral. X=1/2, indicates that the distance between the sub-main and the first emitter is half of the distance that exists between the emitters along the lateral. Example: L = 114 m. distance from the sub-main to the first sprinkler 6 m. Intervals between sprinklers – 12 m. d = 2”, Sprinkler discharge – 1.5 m3 /h. What will be the head-loss in the lateral? The number of sprinklers along the lateral is 10. 114m. – 6m. of the initial section = 108m. 108m./12m. (The interval between the sprinklers) = 9 segments = 10 sprinklers. The total nominal discharge of the lateral: 1.5 m3 /h X 10 = 15 m3 /h. The head-loss in non-distributing 2” lateral will be (from table 10.5): For 100 m. length 13.32 m. For 114 m . length: 13.32m. X 114/100 =15.18m. From table No. 10.6. The F coefficient for 10 emitters (third columns X=1/2) = 0.353. The actual head loss is: 15.18m. X 0.353 = 5.36m. The F coefficient range is from 0.5 for two outlets to 0.33 for more than 100 outlets. Table 10.6. F Coefficient in Laterals Number of Emitters X = 1 X = 1/2 1 1.0 1.0 2 0.625 0.500 3 0.518 0.422 4 0.469 0.393 5 0.440 0.378 6 0.421 0.369 7 0.408 0.363 8 0.398 0.358 9 0.391 0.355 10 0.385 0.353 11 0.380 0.351 12 0.378 0.349 13 0.373 0.348 14 0.370 0.347 15 0.367 0.346 16 0.365 0.345 17 0.363 0.344 18 0.361 0.343 19 0.360 0.343 20 0.359 0.342 22 0.357 0.341 24 0.355 0.341 26 0.353 0.340 28 0.351 0.340 30 0.350 0.339 40 0.345 0.338 50 0.343. 0.337 100 0.338 0.337 >100 0.333 0.335
- 122. SPRINKLER IRRIGATION 101 10.6.2.2. Pressureand Topography The topography in the field affects the pressure in the irrigation system. Elevation of 1 m. in topographic height decreases the pressure by 1 m. (0.1 atm.). Downward decline of 1 m. increases the pressure by 1 m. The slope along the pipe can be expressed in %. That facilitates the calculation of the combined effect of friction in pipes and topography in each point in the field. 10.6.2.3. Nomograms and Slide-rulers In daily use, the common practice of head-loss determination is accomplished by the use of nomograms, slide-rulers and computers. Fig. 10.5. Slide-ruler for Head-loss Calculation in Pipes 10.6.2.4. Head Losses in PVC and PE Pipes The calculation of head losses in PVC and polyethylene pipes is similar to that of aluminum pipes. Since the plastic pipes are designated by their nominal external diameter, it is necessary to know the wall thickness. Knowing the external diameter and wall thickness facilitates the calculation of the internal diameter and the net cross- section of the pipes. These values are required for the calculation of head losses according to the Hazen-Williams formula and for the use of the common head-loss nomograms, in which the internal diameter is the related parameter. As mentioned before, in plastic pipes, as the nominal working pressure is higher, the wall thickness has to be greater and hence the internal diameter and the free cross- section will be smaller. For example, in PE pipes of 50 m m . of 4, 6 and 8 bars. working pressure classes, the greatest internal diameter is in the grade 4 pipe and the smallest is in the grade 8 pipe. For the same flow-rate, the higher head-losses will occur in the 8-grade pipe and the lower in the 4-grade pipe. Two distinct nomograms are given on page 104 for the most prevalent PE pipe diameters of rigid (high density) and soft (low-density) PE pipes. Calculation example: (using the Hazen-Williams nomogram) The head -loss of a 3" aluminum sprinkler lateral with 16 sprinklers, positioned 12 m apart, has to be calculated. The nominal (average) sprinkler flow-rate (discharge) is 1.5 m3 /h; the length of the lateral is 186 m. The friction coefficient [C] of the pipeline is 120.
- 123. SPRINKLER IRRIGATION 102 Solution: The cumulativedischarge of 16 sprinklers with an average discharge of 1.5 m3 /h per sprinkler is 24 m3 /h. A line is drawn in the "Nomogram for The Determination of the Hydraulic Gradient in Pipes" (to the right), from the point A of 24 m3 /h on the flow-rate (Q) scale, through the point indicating the pipeline diameter (D) = 3" on the diameter scale. The drawn line meets the axis of the nomogram in point B. Second line is drawn from the point C that indicates 120 on the C coefficient scale through the crossing point B, which is already marked on the nomogram axis. The line is stretched to the J (head-loss) scale. The point D on the J scale indicates head-loss of 43‰, namely 43 m. per 1000-m length of the pipe. For a 186 m long whole pipeline the head loss is 43 x 186/1000 | 8 m. But the sprinkler lateral is a distributing pipeline. We have to multiply 8 by the F coefficient. The first sprinkler is mounted on the end of the first aluminum 6 m. long pipe, the distance from the sub-main to this sprinkler is a half of the distance between the sprinklers along the lateral that is 12 m. From Table 10.6. F Coefficient in laterals, in the X=1/2 column, it is found that F coefficient for 16 outlets on the lateral is 0.345. Multiplication of this figure (0.345) by 8 m. (the head-loss in 186 m. of non-distributing lateral, depicted from the nomogram) indicates head-loss of 2.76 m. in the lateral. 8 x 0.345 = 2.76
- 124. SPRINKLER IRRIGATION 103 Fig. 10.6.Nomogram for Hazen-Williams Formula
- 125. S P RI N K L E R I R R I G A T I O N 104 Fig. 10.7. Nomograms for Head-loss Determination In Polyethylene Pipes
- 126. 105 S P RI N K L E R I R R I G A T I O N Fig. 10.8. Nomogram for Local Hydraulic Gradient Determination in Accessories
- 127. 106 S P RI N K L E R I R R I G A T I O N Fig. 10.9. Nomogram for Calculation of Head-losses in LDPE Pipes. Class Designation Relates to the Working-pressure (PN) in bar. 1 bar = 10 m Adapted from "Plassim" brochure
- 128. 107 S P RI N K L E R I R R I G A T I O N Fig. 10.10. Nomogram for Calculation of Head-losses in HDPE Pipes. The Class Designation Relates to the Working-pressure (PN) in bar. 1 bar = 10 m. Adapted from "plassim" brochure
- 129. 108 S P RI N K L E R I R R I G A T I O N Fig. 10.11. Nomogram for Calculation of Head-losses in PVC Pipes. The Class Designation Relates to the Working-pressure (PN) in bar. 1 bar = 10 m. Adapted from "Plastro" brochure
- 130. 109 SPRINKLER IRRIGATION 11. WATERMOVEMRNT AND DISTRIBUTION IN THE SOIL 11.1 Introduction The soil has two fundamental functions in growing plants. a. The substrate in which the plant is anchored by means of its root system. b. A source of water and nutrients. Optimized irrigation has to provide water in equal amounts to each of the plants in the irrigated area. Two patterns of water spread on soil surface with pressurized irrigation technologies are recognized. a. Uniform coverage of the irrigated soil surface. b. Localized wetting of the soil surface in such a way that each plant receives equal amount of water. The first pattern is implemented in sprinkler irrigation of field crops, some types of vegetables and overhead irrigation in orchards. The second pattern is common in under-canopy irrigation in orchards and in drip irrigation in all the crops. In order to optimize the irrigation design and management, certain soil properties have to be carefully taken into account. 11.2. Soil Properties 11.2.1. Soil Texture Accurate water application has to be adjusted to soil properties. The soil is created by decaying of rocks into tiny soil particles. The soil preserves its crumbled shape and porosity, with particles that vary in size and are classified according to international conventions. Table 11.1. Soil Classification According to Particle Diameter Fraction Diameter in mm. Clay <0.002 Silt 0.002 - 0.05* Fine sand 0.05* - 0.2 Coarse sand 0.2 - 2.0 *In the American Texture definition code, fine sand diameter is in the range of 0.05 – 0.2 mm. In the International classification code the range is 0.02-0. 2 mm. Different soil types contain particles of miscellaneous size fractions that vary in their ratio. The soil texture is defined accordingly: soil with a high content of large particles is defined as light soil and that with a high content of particles of the fine clay fraction is defined as heavy soil. According to this classification, twelve soil types have been characterized and named, corresponding to the ratio between the different soil fractions. The soil texture determines the water - air ratio in the soil environment. Heavy soil with a high proportion of fine particles has high water holding capacity, but has a low drainage rate and is exposed to surface runoff and insufficient aeration. In light soil with a high content of coarse particles, aeration is adequate but the water holding capacity is low.
- 131. 110 SPRINKLER IRRIGATION Fig. 11.1.Visual Illustration of Soil Particle Diameter (American Classification Code) This method of classification is demonstrated in the Soil Texture Definition Triangle, which is presented in Fig. 11.2. Fig. 11.2. Soil Texture Triangle Adapted from Soil Monitoring Made Easy
- 132. 111 SPRINKLER IRRIGATION 11.3. Soil- Water Relationship 11.3.1. Introduction By consensus there are definitions to the distinctive states of water in the soil. 11.3.2. Saturation When water reaches the soil either as rain, or by irrigation, it infiltrates through the soil surface and percolates downward, driven by gravity. At that point of time the soil is saturated, namely, most of the soil pores are filled with water. 11.3.3. Field Capacity After the rain or irrigation were finished, a fraction of the water continues to drain downwards, driven by gravity. The duration of this movement depends on the structure, texture and other properties of the soil. Water drains from the larger pores where it is replaced by air. 11.3.4. Depletion of Soil Moisture Due to evaporation from the soil surface and absorption of water by plants, the moisture stored in the soil after wetting is gradually depleted. 11.3.5. Wilting Point The soil-moisture content at which the plant fails to absorb water and does not recover its turgor, is expressed as percentage weight per weight (w/w) or volume per volume (v/v) of the soil and designated as the Permanent Wilting Point. LEGEND Soil particles . Water ………... Air ……………. Saturation Field Capacity Wilting Point Fig. 11.3. . Illustration of the Water States in the Soil 11.3.6. Factors Affecting the Differences in Water Storage a. Climate: temperature, radiation, relative humidity, wind, etc. b. Plant: The characteristics of the root system and the leaf area index . Sand Clay Fig. 11.4. Water-air Ratio in Two Soil Types, 12 Hours After Irrigation
- 133. 112 SPRINKLER IRRIGATION 11.3.7. AvailableWater Capacity (AWC) The available water capacity is the difference between field capacity (θθθθfc) and the wilting point (θθθθwp): AVC = θfc - θwp (Eq. 11.1) The available water is the fraction of soil water that can be extracted from the soil by the roots. The amount of water available to the plants differs in diverse soil types and textures. It is not recommended to let the content of the soil moisture reach the wilting point since this may cause damage to the plants. Table 11. 2. Available Water in Different Soil Textures AVAILABLE WATER IN 0 – 100 cm. DEPTH Heavy Clay 1550 m3 /ha Silty Clay 1450 m3 /ha Sandy Loam 1250 m3 /ha Sand 450 m3 /ha Fig. 11.5. Illustration of the Available Water in the Soil 11.3.8. Water Movement in the Soil Water movement in the soil takes place in different dimensions. a. Downwards – driven by gravity. b. All directions – driven by capillarity (cohesion – adhesion forces with the surface area of soil particles and absorption by plant roots). c. Upward – driven by suction of the drying upper soil layers. Essentially the driving force of water movement is the difference in water potential. Water potential is the inherent free energy attained by the water in certain point, Table 11.3. Average Values of Water States in Different Soil Textures – WW % SOIL TEXTURE θfc θwp AVC Coarse Sand 10 5 5 Sand 15 7 8 Loamy Sand 18 7 11 Sandy Loam 20 8 12 Loam 25 10 15 Silty Loam 30 12 18 Silty Clay Loam 38 22 16 Clay Loam 40 25 15 Silty Clay 40 27 13 Clay 40 28 12
- 134. 113 SPRINKLER IRRIGATION capable toperform work. The work done can be the relocation of water from one point to another. As mentioned before, water potential units are bars, atmospheres or kilopascal (Kpa). Soil water potentials are mostly negative pressures (tension or suction). Water flows from a higher (less negative) potential to a lower (more negative) potential. The water potential reflects how much energy plants have to spend in water extraction. Fig. 11.6. Water Potential Values in the Different Water States in the Soil 11.3.8.1. The Components of the Water Potential ψψψψt = ψψψψg + ψψψψm + ψψψψo (Eq. 11.2) a. ψψψψt = Total soil water potential b. ψψψψg = Gravitational potential (force of gravity on the water) c. ψψψψm = Matric potential (force exerted on the water by the soil matrix – soil water “tension”) d. ψψψψo = Osmotic potential (due to the difference in salt concentration across a semi-permeable membrane, such as a plant root) The matric potential, ψm, normally has the greatest effect on release of water from soil to plants.
- 135. 114 SPRINKLER IRRIGATION 11.3.8.2. SoilWater Retention Curve a. That is the curve of matric potential (tension) vs. water content b. Less water → more tension c. At a given tension, finer-textured soils retain more water ( due to the larger number of small pores) Fig. 11.7. Water Retention Curves in Different Soil Textures 11.3.9. The Determination of the Water Status in the Soil The determination of the water amount that has to be applied by irrigation can be done with different methodologies: 11.3.9.1. Climatic indicators are correlated to the rate of evapo-transpiration of the plant. A common practice is the measurement of the evaporation rates of water from a Class A pan. The daily water consumption of the crop can be estimated by the multiplication of the measured evaporation rate in mm/day by the Crop Coefficient. Another climatic method for the estimation of crop water requirements is the using of Penman equation, in which climatic factors such as temperature, sun radiation, wind velocity, etc., are measured and the potential evapo-transpiration is calculated. The most common used and practical indicator is soil moisture. It can be measured directly with the gravimetric method.
- 136. 115 SPRINKLER IRRIGATION Fig. 11.8.The Sequence of Soil Moisture Determination by the Gravimetric (Oven Drying) Method Fig. 11.9. Edelman Dutch Auger Soil samples are taken with soil auger and transferred to the laboratory. Each soil sample is weighed and dried for 24 hours in a drying oven at 105 0 C and then weighed again. The difference in weight before and after heating resembles the water amount in the soil. The water content is expressed as the percentage of the dry weight of the sample. For the determination of the water percentage per volume, which is more relevant in the calculation of water application, the percentage per weight is multiplied by the bulk density. Soil moisture can also be determined in different methods and instrumentation. The topic is dealt in more detail in the chapter on monitoring. 11.3.10 Water Intake Rate (WIR) of the Soil Water intake rate of a certain soil is designated with the term infiltrability. It refers to the infiltration rate resulting when water at atmospheric pressure is made freely available at the soil surface. The water infiltration rate into the soil is a key parameter in the design and operation of sprinkler irrigation systems. It indicates how fast - in mm/hour units - water infiltrates into the soil. Commonly, the intake rate decreases over time during the time of irrigation. In clay or silty soil, the infiltration rate declines sharply during the water application time. For Example: In the first half-hour the rate is 20 mm/h. After 1 hour: 12 mm/h. After 2 hours: 8 mm/h. After 3 hours: 5 mm/h and after 4 hours - 4 mm/h. Due to the compaction of the soil by mechanized tillage, the infiltration rate declines during the irrigation season. Fig. 11.10. Curves of Water Infiltration into the Soil
- 137. 116 SPRINKLER IRRIGATION Fig. 11.11.Soil Texture Triangle – Infiltration Rate Contours Figure 11.11. presents typical infiltration rates in different soil texture types. The presented values only relate to the difference in the soil texture. The intake rate depends on additional factors, such as soil structure, cultivation practices, organic matter content and salinity of the soil. These values should only be used as a rough guideline, and, wherever possible, field tests should be done for the determination of the actual steady state infiltration rate. Fig. 11.12. demonstrates the Fig. 11.12. Typical Infiltration Curves in Different Soil Textures
- 138. 117 SPRINKLER IRRIGATION change ofthe infiltration rate along time in three soil types. The Water Intake Rate (WIR) of the sand starts at 250 mm/h and becomes nearly constant at 25 mm/h after 90 minutes. The WIR of the silty clay soil decreases within 30 minutes from 50 mm/h to zero. 11.3.10.1. Determination of the Water Intake (Infiltration) Rate Measurement of water intake rate is implemented with two different conceptual methods: a. Flood simulation, in which the impact of water drops on the soil surface is not pronounced. b. Sprinkling methods, in which the water drops may deform the structure of the upper soil layer, induce encrustation and decrease the infiltration rate. These techniques are more relevant to sprinkler irrigation. The most prevalent techniques of the flood manner employ the basin infiltrometer and the double ring infiltrometer. 11.3.10.1.1. Basin Infitrometer a. Basic Measurement b. Refined Arrangement of the Instrumentation in the Basin Method After S. Dasberg, I. Hausenberg and O. Kramer Fig. 11.13. The Basin Infiltrometer In the basin infiltrometer, soil from the outside of the basin is taken to build the paired dykes, thus not deforming the soil within the dyked area. The size of the water flooded area, 1m2 – 10m2 . The disadvantages of this infiltrometer are the disruption of the soil upper layer and the labor needed to build the basins and apply the water. Marr of the University of California at Davis had proposed an elaborated method. He suggested measuring of the water infiltration rate in two phases. a. Measurement of the infiltration rate during the beginning of water application. b. Measurement of the infiltration rate after the stabilization of the infiltration rate. The precipitation rate of the sprinkler irrigation system should never exceed the water intake rate. If the precipitation rate is higher than the intake rate, water logging will occur and runoff may cause erosion of the upper soil layer. The measured values have to be taken into account in the selection of the emitter type and its flow-rate, as well as in the design of the positioning of the sprinklers in the field and the scheduling of the irrigation.
- 139. 118 SPRINKLER IRRIGATION 11.3.10.1.2. Double-ringInfiltrometer The double-ring infiltrometer is the most common type of infiltrometer used. It is inexpensive to put up and operate, requires relatively little water amount compared with the basin infiltrometer. One person can set-up and run several tests simultaneously. The simplicity of its design allows for ease in replication and operation. Fig. 11.14. Double-ring Infiltrometer Two concentric rings of stainless steel are commonly employed, the larger ring forms a buffer compartment around the inner to account for lateral flow (Fig. 11.14). The rings are jacked or hammered into the ground 5 - 10 cm. deep. Care is taken to minimize distortion of the soil surface and the soil structure during installation. A specific and constant head of water (less than 5 cm of depth) is maintained in both rings, while the rate of water depletion from the inner ring is measured. The length of time required to achieve steady infiltration rate ranges from 2 to 6 hours, depending upon soil type, texture, and antecedent soil moisture conditions. 11.3.10.1.2.1. Mariotte Double-ring Method The device used in the Mariotte double-ring method consists of two major components: the cumulative infiltration measurement device comprising a Mariotte bottle, modified double rings and an apparatus for soil water content measurement by gamma ray detection, built of a radioactive source, detector and access tube. The Mariotte bottle controls the water supply to the inner ring. This improves the accuracy of the applied water amount during the measurement process. The gamma ray detector monitors the soil water content change over time in the soil profile. The relative error is estimated by comparing the cumulative infiltration and the water content distribution using the mass balance principle. The Mariotte double-ring technique improves the accuracy of the double-ring method. The real-time distribution of the water during the measurement can be observed to estimate the relative error in the measurement.
- 140. 119 SPRINKLER IRRIGATION The experimentalapparatus of the Mariotte double-ring method is relatively complicated and expensive for use in field experiments. As in the ordinary double- ring method it is limited to level soil surfaces and commits deformation of the initial soil structure. There is also a potential hazard to the health and safety of the operator when using the radioactive gamma-ray source. 11.3.10.1.3. The Sprinkler Method Sprinklers are operated in optimal spacing with a known application rate in an area where a ring of a 30-50 cm diameter is inserted a few cm deep into the soil. The water movement on the soil surface is confined by the ring. The excess water that is not absorbed by the soil inside the ring flows into a large graduated cylinder sunk into the soil aside the ring. The infiltration rate measurement starts as soon as water begins to drain into the cylinder. Once the water amount per time unit that had been applied within the ring (Q1) and the accumulated water amount in the cylinder (Q2) are known, it is possible to calculate the water quantity (Q1-Q2) that infiltrated within the ring during that time. The “Sprinkler Method” is the best practice for the determination of the WIR for sprinkler irrigation systems since it resembles the effects of the impact of the water drops on the encrustation of the soil surface. 11.3.10.1.4. Rain Simulator A more sophisticated technique for measuring the infiltration rate is by using rain simulator. Rain simulators are used for measurement of the impact of rainfall and irrigation drops on runoff and infiltration. Because of the high cost and complicated operation, it is used mainly in research and is not relevant to routine measurements in the field. 11.3.10.2. Infiltration in Micro-irrigation Micro-sprinklers and micro-jets wet discrete soil volumes with or without partial overlapping. The wetted soil surface area is a small fraction of the total soil surface area in the plot. Water movement within the soil follows a three-dimensional flow pattern, contradicting the one-dimensional, vertical percolation pattern typical of flood and full surface coverage sprinkler irrigation. Two driving forces affect simultaneously the flow of water in the soil: gravity and capillarity. Gravity drives the water downwards. Capillary forces drive the water in all directions. The equilibrium between these two forces determines the pattern of water distribution within the soil. The wetting pattern affects the distribution of roots in the soil as well as the dispersion and accumulation of dissolved nutrients and salts. Fig. 11.15. The “Sprinkler Method”
- 141. 120 SPRINKLER IRRIGATION 11.4. SoilWetting Patterns The key factors affecting the pattern of water and solutes distribution in the wetted soil volume are: a. Soil properties b. Emitters' position and spacing c. Emitter water distribution pattern d. Emitter flow-rate e. Water dosage f. Chemical composition of the Water In addition to soil texture, mentioned before, soil structure also affects water distribution. Compact layers and horizontal stratification increase the horizontal flow of water at the expense of vertical percolation. On the other hand, vertical cracking in compacted soils amplify a preferred downward flow of water followed by incomplete wetting of the upper soil layers. 11.4.1. Water Dosage The wetted volume expands and gets deeper as the amount of applied water increases. 11.4.2. Chemical Composition of the Water Dissolved chemical compounds in the water may affect the wetting pattern. Detergents and other surfactants contained in reclaimed and storm waters reduce water surface tension and decrease the horizontal flow. The lower surface tension increases the effect of gravity at the expense of the capillary forces, resulting in a narrower and deeper wetted volume. 11.5. Water Distribution Uniformity The excellence of irrigation is evaluated by the Irrigation Efficiency (IE), which is defined as: waterappliedtotal usedlybeneficialwater IE = (Eq. 11.3) Water beneficially used comprises of the water consumed by evapo-transpiration and that used for fertilizer and pesticide application, salt leaching from the soil, crop cooling and frost protection As mentioned before, there are two principal patterns of water distribution in irrigation. a. Full and uniform wetting of the soil surface, as in overhead sprinkler irrigation and border surface irrigation. b. Localized water application as in drip irrigation, furrow and under-canopy orchard sprinkler irrigation. The uniformity of water distribution is one of the most important features of successful crop production. Low water distribution uniformity can bring about non- uniform crop development, stunted growth and excessive vegetative growth in the same field. Non-uniform water distribution can impair soil aeration and bring about leaching of plant nutrients in one sector and accumulation of harmful salts in the root- zone in another.
- 142. 121 SPRINKLER IRRIGATION The criteriafor distribution uniformity are quite different in the two patterns of water distribution mentioned above. High water distribution uniformity over the whole soil surface is not unattainable , nor is it necessary in localized irrigation techniques. Water distribution in localized irrigation is regarded satisfactory if each plant within the irrigated area receives the same volume of water. Getting this objective requires an appropriate layout of the irrigation system. In those irrigation techniques that distribute irrigation water over the whole soil surface, it is imperative to achieve a high degree of water distribution uniformity. In practice, absolute uniformity is unattainable. The variance of the components of the irrigation system and the topography, among other factors, impede 100% uniformity. 11.5.1. Distribution Uniformity in Fully Soil Surface Wetting Irrigation Three methodologies have been developed for estimating water distribution uniformity by sprinkler irrigation over the whole area. All three are based on the measurement of the water distribution over an area between adjacent sprinklers. 11.5.1.1. Distribution Uniformity (DU) is a uniformity concept originally suggested by the Soil Conservation Service of the U.S. Department of Agriculture. It is the ratio between the average application depth on that quarter (25%) of the area receiving the least irrigation water dosage and the average application depth over the whole wetted area. DU is expressed at percentage units. (Eq. 11.4) 11.5.1.2. Coefficient of Uniformity (CU), formulated by J. E. Christiansen, is the second way for estimating sprinkler irrigation uniformity. (Eq. 11.5) Where: CU = Coefficient of Uniformity (%). XI = Individual readings X = mean value of the readings n = number of readings There are linear relationships between CU and DU. CU = 0.63 DU + 37.0 (Eq. 11.6) DU = 1.59 CU - 59.0 (Eq. 11.7) 11.5.1.3. Scheduling Coefficient (SC). It is an uniformity standard used mainly in turf irrigation. In this environment, even relatively small areas of inadequately watered turf show up with high visual impact. The ratio between average application depth in the whole irrigated area and application rate in a defined critical area that shows water deficiency symptoms. SC is the factor by which the net amount of water application has to be increased, in order to compensate for non-uniformity. SC is a number greater than or equal to one. SC = 1.0, indicates perfect uniformity. SC = 1.5,
- 143. 122 SPRINKLER IRRIGATION indicates thata 50% increase in watering amount is needed to compensate for non- uniformity. The SC can be computed for critical areas of different sizes. The commonly used values are 1%, 2%, 5% and 10% of the irrigated area. Even the largest of these areas is considerably smaller than the low quarter (25%) used in the DU computation. SC calculated on a 5% fraction yields appropriate results in most practical situations in turf irrigation. (Eq. 11.8) In all of the three procedures the measuring of the water application uniformity is done by the position of water collecting containers (cans of 200 – 500 ml. volume), in a grid with 0.25 – 2 m. spacing between the cans. Distribution tests can be done under different wind velocities. The basic nominal data relate to non-windy conditions. 11.5.1.4. The Single Sprinkler Test The sprinkler is operated at a consistent pressure for 3 - 4 hours. Both the position of each can and the volume of water in the cans are registered at the end of the test period. Wind velocity and its direction, as well as the rate of the sprinkler rotation (revolutions per minute) and its flow-rate are recorded during the test. The distribution pattern of the sprinkler may be plotted. The uniformity of application for different spacing between the sprinklers can be determined by virtual overlapping imposition of the sprinkler distribution pattern. The drawback of this procedure is its reliance on theoretical overlapping and the relatively long term of the test (3 - 4 hours), due to the small amount of water that accumulates in the cans. Care must be taken to ensure that the tested sprinkler is a representative sample and the test results should be replicated. In this method a larger number of cans have to be positioned than in the other procedures. Due to the relatively long period that is required to measure the water accumulation in the cans, care should be given to avoid evaporation from the cans. Fig. 11.16. Single Sprinkler Test
- 144. 123 SPRINKLER IRRIGATION 11.5.1.5. TheSingle Sprinklers-lateral Test A single lateral is operated with the sprinklers mounted at pre-defined spacing intervals. Four sprinklers will generally suffice, provided that the sprinkler radius of coverage does not exceed twice the spacing between the sprinklers on the lateral and the wind does not cause water drift in the parallel direction to the lateral. This method is the closest to field conditions in hand-move sprinkler irrigation when laterals are not operated simultaneously in adjacent positions. The test demonstrates the actual water distribution on either side of the lateral. By virtual overlapping the data from two adjacent laterals, the distribution uniformity may be calculated for different lateral spacing. The test should last at least 2 hours. 11.5.1.6. The Simultaneously Operated Laterals Test. Four sprinkler laterals, with at least 4 sprinklers mounted on each one of them, are operated simultaneously. The cans are set between the 4 central sprinklers of the central laterals. If the radius of coverage of the sprinkler exceeds twice the spacing between the sprinklers, more than 4 laterals and 16 sprinklers are needed. The number of cans to be measured in this method is less than in the former check and test duration can last only one hour. This method allows for the calculation of the distribution uniformity only for the spacing tested. The test results are analyzed with the Christiansen formula. Satisfactory coefficient of uniformity (CU) has to be of 84% or more. In optimal field conditions, 90% and higher values are achievable. Distribution uniformity below 84% is non-satisfactory and may render waste of water and growth disturbance. Fig. 11.19. Open-air Test Plot (left) and Covered Distribution Test Facility (right) Fig. 11.17. Single Lateral Test Fig. 11.18. Simultaneously Operated Laterals Test
- 145. 124 SPRINKLER IRRIGATION Fig. 11.20.Grid of Catch Cans
- 146. 125 SPRINKLER IRRIGATION Fig. 11.21.Recording Form for Measurement of the Uniformity of Water Distribution
- 147. 126 SPRINKLER IRRIGATION Fig. 11.22.Measured Water Amounts in One Quarter of the Wetted Area in Single-sprinkler Test a. One Dimensional View b. Concentric Wetting Pattern Presentation Fig. 11.23. Single Sprinkler Distribution Pattern in Wind-less Conditions
- 148. SPRINKLER IRRIGATION 127 Table 11.4Calculating Christiansen's Coefficient of Uniformity with Experimental Data (example): (1) (2) (3) (4) (5) Readings No of Readings R X n Abs. Dev. From Av. (R) (n) (1) X (2) (d) (2) X (4) 100 1 100 24 24 102 2 204 22 44 104 1 104 20 20 106 2 212 18 36 108 2 216 16 32 110 6 660 14 84 112 114 2 228 10 20 116 3 348 8 24 118 5 590 6 30 120 1 120 4 4 122 5 610 2 10 124 4 496 0 0 126 1 126 2 2 128 4 512 4 16 130 6 780 6 36 132 3 396 8 24 134 6 804 10 60 136 6 816 12 72 138 3 414 14 42 140 142 1 142 18 18 144 1 144 20 20 146 1 146 22 22 Total 66 8168 - 640
- 149. SPRINKLER IRRIGATION 128 Fig. 11.24.Wind Effect on the Distribution Pattern on Both Sides of a Single Lateral Fig. 11.25. Unilateral Presentation of the Distribution Pattern of a Mini-emitter
- 150. 129 SPRINKLER IRRIGATION 11.5.2. DistributionUniformity in Localized Irrigation 11.5.2.1. Overview As mentioned before, application uniformity can be expressed in different indices. A uniformity of 100% means that the whole irrigated plot has received exactly the same amount of irrigation water everywhere. In low uniformity values, some parts of the plot receive less water than others and it is necessary to apply excess water so that the plants growing in the areas that receive less water will not suffer water deficiency. The common index for indication of the application uniformity in localized irrigation is the before mentioned DU (Distribution Uniformity). Contradicting to the test of CU that relates to distribution uniformity on the irrigated area (soil surface), The DU index relates toapplication uniformity of the water emitters. To calculate this value, the flow- rate of a representative sample (40 - 100 emitters in different regions of the irrigated plot) is measured. Q25% DU = 100 X Qn (Eq.11.9) Where: Q25% is the average flow-rate of 25% of the emitters with the lowest flow-rate, Qn is the average flow-rate of all the sampled emitters. DU values above 87% indicate excellent distribution uniformity; 75% - 87% - good uniformity; 62% - 75% acceptable uniformity and below 62% the uniformity is unacceptable. Variation in the flow-rate depends on the pressure regime, partial emitter clogging and the manufacturing variance of the drippers. In addition to variation in flow-rate between emitters due to pressure difference, flow- rate deviations occur also because of manufacturing variability. No two emitters can be identically manufactured; some variation will exist between the emitters. New emitters' flow-rate uniformity is designated by the Manufacturing Coefficient of Variation (Cvm). The manufacturing coefficient of variation Cvm is defined as the standard deviation divided by the average flow-rate from a sample of emitters. It is expressed as a decimal fraction or percentage. 0.01 = 1%. According to the formula: Cvm = Sdm/Xm (Eq. 11.10) where, Cvm = manufacturing coefficient of variation, Sdm = standard deviation, Xm = mean flow-rate. A Cvm of 0.1 (10%) means, assuming normal distribution “bell shaped” curve that 68% of all emitter flow-rates would be within ±10% of the mean flow-rate. The design of the emitter, the materials used in its construction, and the precision in which it is manufactured, determine the variation for any particular emitter type. A Cvm of 0.05 or less is considered excellent, 0.05 - 0.10 is good, 0.10 - 0.15 is marginal, and more
- 151. 130 SPRINKLER IRRIGATION than 0.15is poor. With the recent improvements in manufacturing tolerances, most emitters have Cvm < 0.10. The manufacturing flow-rate variation is determined statistically. Samples of emitters are selected randomly and tested under constant pressure. 11.5.2.2. Emission Uniformity (EU), combines variation due to emitter manufacturer variance and variation due to pressure. This is a design parameter. In new installations or when emitter clogging is not occurring, EU (design) is approximately equal to DU. EU is given as: EU = [(1 -1.27(Cvm)) X (Qn/Qavg) X 100] (Eq. 11.11) Where, Cvm = manufacturer’s coefficient of variation, Qmin = minimum emitter discharge due to reduced pressure, Qavg = mean emitter discharge due to pressure.
- 152. 131 S P RINK LE R I R R I G A T I O N 12. SPRINKLER IRRIGATION TECHNIQUES 12.1. Overview Sprinkler systems can be classified in two broad categories: set and mobile systems. Set Systems can be further divided into fixed and periodic-move systems. Mobile Systems can be further divided into intermittent-move and continuous-move systems. Three criteria determine the selection of the optimal sprinkler irrigation method. a. Crop type: e.g. field crops, orchards, greenhouses, etc. b. The type of emitter: overhead, under-canopy, microsprinklers, etc. c. The degree of mobility: hand-move, solid set, towline, wheel-move, traveler, linear- move, center-pivot, etc. The available equipment, crop requirements, economical considerations and the availability, qualification and cost of manpower, determine the selected irrigation method. Sprinkler laterals are made of aluminum and plastic materials. In Linear-Move and Center-Pivot, the main lateral may be made also of high tensile galvanized light steel. 12.2.Hand-move 12.2.1. Aluminum Pipes Fig. 12.1. Hand-move Lateral laterals of 2" and 3" diameter, 6 or 12 m. long segments are moved manually from one position to another. Each lateral is transferred several times to different positions during the irrigation cycle. At the beginning of the next irrigation cycle, the laterals are moved forward along the distribution line and the terminal lateral is returned to the first position in the field. This scheme is known as the "clock method" and is widely used. The hand-
- 153. 132 S P RINK LE R I R R I G A T I O N move technique is usually applied in small plots of field crops, vegetables and orchards, As well as in fields that are not suitable for mechanized irrigation and solid set systems are beyond owner's financial capability. The technique is labor consuming and commits physical effort. Fig. 12.2. Hand-move Layout: 2” Aluminum Pipes, Spacing 6X12 m. 4 Laterals X 4 Positions Legend for Drowings = Head at that point – m. = Flow-rate – m3 /h and flow direction = Pipe material and nominal diameter = Width/length – m. = position No. # 12.2.1.1. Labor Requirements Two hours of labor are required for the irrigation of one hectare of cotton at sprinkler spacing of 12 m x 18 m; including the positioning of laterals in the field, removal, transfer, etc. Four hours of labor is required for the irrigation of one hectare of vegetables at spacing of 6 m x 12 m. 12.2.1.2. Hand-move Operation Recommendations a. Coupling and uncoupling of pipes should be done holding the center of gravity of the pipe, b. The lateral has to be flushed with a small water flow during the assembling of the laterals. c. On the way back to the head of the lateral, the coupling sealing, the stability and verticality of the sprinklers and their performance has to be checked. d. In tall crops, such as cotton or corn, footpaths between the plants should be prepared to ease the moving and positioning of pipes. e. When using pipes 12-m. long for irrigation of tall field crops, the saddle with the Fig. 12.3. Coupling of Aluminum Pipe
- 154. 133 S P RINK LE R I R R I G A T I O N sprinkler should be mounted in the center of the pipe. f. Pipes should not be carried vertically to avoid the hazard of contact with electrical wires. g. At the end of the irrigation season the equipment should be stored and serviced. 12.2.2. Flexible Laterals in Orchards Soft polyethylene laterals (grade 6) of 16, 20 or 25 mm diameter, up to 50 m-long, with one or two sprinklers at the distal end of the lateral are pulled along the rows of the trees. At the start of the irrigation cycle, the lateral is fully stretched between two rows of trees. At the end of the first shift the lateral is pulled to its next position along the row of trees and so on until the cycle is completed. The laterals are returned to the starting position, by a "large move" and wait for the next irrigation cycle. The number of positions per lateral may vary, depending on the conditions in the orchard. Normally, The number of positions varies between 2 to 6. When irrigating two shifts per day, the number of shifts in a cycle can be doubled. The irrigator steps on dry soil, does not cross rows of trees when pulling the laterals, and work output is higher than with hand-move of aluminum pipes under the same circumstances. The method is inexpensive due to the small number of sprinklers needed but the wear of the laterals is high due to fracturing of the laterals. Accuracy in positioning is required as well as skilled and permanent manpower. Fig. 12.4. Ten Shift Manual Drag Under-Canopy Sprinkler Array
- 155. 134 S P RINK LE R I R R I G A T I O N 12.3. Permanent Installations 12.3.1. Solid-set in Orchards 12.3.1.1. Under-canopy Irrigation Soft polyethylene (grade 4) pipes of 16, 20 or 25 mm diameters are laid-out along the rows of the trees beside the trunks. Low-volume sprinklers, mini and micro-sprinklers or micro-jets (flow-rate up to 250 l/h) are mounted on the pipes or connected by means of a small-diameter plastic tube. Precipitation rate is low, 3 - 5 mm/h. The distance between the emitters along the lateral corresponds to the tree spacing, one emitter per one or per two trees. The sub-mains are commonly made of HDPE pipes of grade 4 or 6 bar working presssure. Manifolds are buried underground across the tree rows. In case of hazard for damage by woodpeckers, the laterals also should be buried in the shallow upper soil layer. Fig. 12.6. Solid-set System in Orchard. Spacing 6 X 4 m. Sprinkler Flow-rate 100 l/h Despite the high cost of this technology, the solid-set systems are replacing the hand- move irrigation in orchards. Micro-emitters, as well as drippers, are the prevailing emitters used. Figure 12.5. Orchard Under-canopy Micro-sprinkler Irrigation
- 156. 135 S P RINK LE R I R R I G A T I O N Solid-set systems save labor, are conveniently operated and are compatible with all the types of automatic control systems. The low angle of water throw prevents wetting of the canopy, decreasing the occurrence of leaf-diseases and washing-out of pesticides from the leaves. Wind impact on the uniformity of water distribution in mature orchards is negligible. The system can be used to moderate extreme temperatures and reduce the damage during events of frost or heat spells. Fertigation is common in solid-set systems in orchards. The short irrigation intervals and the improved control on wetting depth increase the efficiency of nutrient application. 12.3.1.2. Overhead Orchard Irrigation HDPE pipes, 40-75 mm in diameter, grade 4, are stretched along the rows beside the trees. The sprinklers are mounted on high risers, at least 25 cm. above the tops of the trees. The position of the sprinklers will be every second or third row and 10 – 15 m. apart along the lateral, in accordance with tree spacing and plot dimensions. In order to keep costs low, the spacing is as wide as possible, keeping acceptable distribution uniformity. Installation and operation are simple, labor investment is minimal and complete coverage will be attained if the sprinklers' position and operation pressure are adequate. There are, however, some limitations: High working pressure and low salt content in irrigation water are required. Irrigation can be applied only at night. There is water losses in plot margins, particularly in small plots. The wetting of the foliage enhances leaf and fruit fungal and bacterial diseases. Fig.12.7. Orchard Overhead Irrigation In recent years, under-canopy solid-set technology is replacing the above canopy systems in orchards, apart from in those circumstances when overhead irrigation is significantly more efficient in decreasing frost damage. 12.3.2. Mini-sprinklers Solid-set Systems in Vegetables From the last decade of the 20th century, there has been a wide-scale expansion of the
- 157. 136 S P RINK LE R I R R I G A T I O N use of low-volume mini-sprinklers in solid-set irrigation systems in vegetables grown in open fields. The emitters are modified orchard under-canopy mini-sprinklers with extended wetting diameter that allow spacing of 8X8 and 10X10 m. The initial investment is lower than in solid-set dripper systems or laterals with the common general use sprinklers. The working pressure is relatively low and the economical results are satisfactory. The laterals are of 40 - 50 mm. diameter. The mini-sprinklers are connected to the laterals by means of thin flexible tubes and are supported by 100 - 150 cm long metal rods that are inserted into the soil, to guarantee the vertical position of the emitters. The common sprinkler flow-rate is 400 - 600 l/h and precipitation rate is 4 - 6 mm/h. One more advantage of this technology is the reduction in encrustation of the soil surface and runoff prevention, due to the low irrigation intensity. The major limitation of this technique is its sensitivity to wind. Fig. 12.8. Solid-set Mini-sprinkler Irrigation of Vegetables
- 158. SPRINKLER IRRIGATION 137 12.4. MechanizedIrrigation 12.4.1. Introduction The shortage of skilled man-power as well as the accelerated shift from surface to pressurized irrigation and the necessity to simultaneously irrigate vast areas, triggered the development of mechanized irrigation. The simplest mechanized technologies are the towline as a replacement to hand-move of aluminum pipes and the mechanized side-roll as a modification of the manual wheel-move. Later on, more advanced systems were elaborated: the traveling-gun (traveler), the Center-Pivot and the Linear-Move laterals. Mechanized irrigation is suitable for large rectangular plots, over 10 - 20 hectares in flat land or moderate slope. Mechanized irrigation of irregular plots has lower irrigation efficiency and relatively high water losses. 12.4.2. Towline a. In Work b. Closeup of a Segment with Stabilizer Fig. 12.9. Towline Towlines consist of ordinary, 12 m. long aluminum pipes. Reinforced couplers fasten together the pipes, in order to minimize the risk of disintegration during towing. The pipes are supported by skids or wheels spaced 6 - 12 m. apart. The riser is mounted in the middle of each pipe segment, for better stability during towing. The risers should be high enough that the sprinklers will be located above the plants' canopy. A common towline lateral length is up to 400 m., when 4" aluminum pipes are used. When 3" pipes are used, lateral length limit is 250 m. Automatic quick drain valves are located at the bottom of each coupler to allow fast drainage of water from the lateral after shut- Fig. 12.10. Towline Accessories
- 159. SPRINKLER IRRIGATION 138 off ofthe water. An empty line requires less power to be dragged to its next set, wear of the system and soil compaction are reduced. As mentioned before, two carriage types are available. One is a skid plate attached at each coupler for raising slightly the pipe off the soil, protect the quick drain valve and reduce the friction with soil surface when the pipe is towed. Two or three stabilizers are required per 400 m. of lateral to keep the sprinklers upright. The other carriage type is consisted of small metal wheels at 12 m. intervals along the lateral to raise the pipe and allow it to be easily towed. Towing is performed longitudinally along the rows. The laterals are towed by tractor from one position to the next. The number of tow positions will be twice the number of distribution lines. Commonly, laterals are towed 6 positions but there are also fields with 4,8 or even more positions. Fig.12.11. Linear Towline System: 2 Sets, 8 Laterals Each, Six Positions per Lateral, Spacing 12X18 m. 12.4.2.1. Comparison Between Solid-set and Towline At a spacing of 12 x 18 m, six hundred meters of aluminum pipes are required per one hectare of solid-set system, while when pipes are towed, 100 m. length is sufficient for the same area. The towline system is economical for crops which require a high frequency of irrigation. Consequently, the technology was extensively used in field crops and fodder crops. During the last three decades, mechanized Linear-Move laterals and Center-Pivot systems have replaced the towlines when investment money was available. 12.4.3. Wheel-move Wheel-move systems have three variants: a. Traditional manually moved sistems b. Side-roll systems c. Side-move systems Manually move sytems were limited in length – up to 200 m. and in many cases, more than one irrigator was needed to relocate the system. Nowadays it had been almost fully replaced by the mechanized side-roll and side-move systems. 12.4.3.1. Side-roll Systems Side-roll or wheel-line systems use an aluminum or galvanized steel lateral as water conveyer and also as the axle of a large (1.5 - 2.0 m diameter) wheels. The wheels are spaced 9 – 12 m apart and allow the lateral to be rolled from one irrigation
- 160. SPRINKLER IRRIGATION 139 position tothe next one. A small internal combustion engine is used to roll the whole lateral. The pipes must be strong, and rigid couplings are used to withstand the high torque loads. Usually, the engine is located in the middle of the lateral to reduce the torque. Ordinary impact sprinklers, spaced 9 - 12 m. apart, are mounted on a special weighted swivel assembly to secure their upright position after each move. Before irrigation begins, the main-line is laid along the side of the field. When irrigating, the lateral remains in place until the designed water amount has been applied. A flexible hose connection to the hydrant allows the lateral to be moved over two or three sets with water supply from the same hydrant. This system is best suited to large flat rectangular areas of low field crops. In heavy soils, the wheels may become bogged-down in the mud. The aluminum or galvanized steel pipe, is of 3" – 6" in diameter. As mentioned before, the pipe serves also as the axle of the metallic wheels. The greatest length of the lateral is 300 – 400 m. In some exceptional circumstances it can be extended up to 600 m. The sprinklers are mounted along the lateral on swiveling connectors equipped with ballast to secure the vertical position of the riser. The width of the irrigated area in each position depends on the sprinkler specifications. Commonly it ranges from 20 to 30 m. The engine that is mounted in the middle of the system propels the wheels by means of a drive-shaft from one irrigation stationary position to the next. During the movement, the water is closed. The duration of irrigation in each position is 3 - 12 hours, until the pre-designed water amount has been applied and the water is automatically shut-off. Then the operator disconnects the system from the hydrant, starts the engine and moves the system forward to the next position, 12 - 24 m. ahead, where he connects the system to another hydrant. The side-roll is suitable for flat terrain and slopes up to 5%. Fig. 12.12. Sprinkler Vertically Stabilized by a Swivel and a Ballast
- 161. SPRINKLER IRRIGATION 140 Fig. 12.13.Side-roll Operating Scheme The side-roll sprinkler system is best adapted for rectangular fields. The operating pressure is 2.5 – 4.0 bars with impact sprinklers. Since the lateral pipe to which the sprinklers are attached also acts as the axle for the wheels, crop height is a limiting factor. The flexible hose is used to connect the system to the hydrants that are located mostly along the edge of the field. One shift usually covers 1 – 2 hectares, so one side-roll system can cover 10 – 20 hectares per system. The side-roll has medium labor requirements and a moderate investment cost. Fig. 12.14. Side-roll in the Field 12.4.3.2. Side-move Systems The difference from the side-roll is that in this variant, the lateral pipe is not used as an axle to the wheel. The pipe is mounted segmentally on a frame with two wheels
- 162. SPRINKLER IRRIGATION 141 per segment.Hence the pipe location can be higher and allows irrigation of higher crops. The pipe is not rotating and the risers are fixed and does not need the vertical stabilization with swivels and ballasts. 12.4.4. Traveling-gun (Traveler) 12.4.4.1. Overview The traveling-gun has been emerged from the manually moved big-gun. Gun (Giant, or Rain Gun) sprinklers have 16 mm or larger nozzles attached to long (30 or more cm.) discharge tubes. Most gun sprinklers are rotated by means of a rocker-arm drive and the majority can be set to irrigate a part circle. Boom-sprinklers have a rotating 35 – 75 m. long boom, supported in the middle by a tower mounted on a trailer. The tower serves as the pivot for the boom that is rotated once every 1 to 5 minutes by jets of water discharged from nozzles. The nozzles are spaced and sized in such a template that applies a fairly uniform application of water to a circular area of 80 – 100 m. in diameter. Tower movement is periodic and accomplished manually. Gun or boom-sprinkler systems can be used in similar situations and are principally compatible with supplemental irrigation and for use on irregularly shaped fields with obstructions. Each of the two types has its comparative advantages and disadvantages. Gun-sprinklers are considerably less expensive and are simpler to operate; consequently, there are many more guns than boom-sprinklers in use. However, guns require high pressure of 5 – 10 bars and energy costs are higher. Gun and boom-sprinklers usually discharge more than 25 m3 /h and are operated individually rather than as sprinkler-laterals. A typical sprinkler discharges 100 m3 h and requires 50 – 70 m. (5 – 7 bars) or higher operating pressure. Gun and boom-sprinklers can be used for irrigation of most crops, but they have relatively high application-rates and large water drops that tend to compact and seal the soil surface and induce runoff and soil erosion. The meaning is that these sprinklers are most suitable for coarse-textured soils having high infiltration rates and for mature crops that need only supplemental irrigation. Gun and boom-sprinklers are usually not recommended for use in extremely windy areas because their distribution patterns may become too distorted by the wind. Large gun-sprinklers are usually trailer or skid mounted and like boom- sprinklers are towed from one position to another by a tractor. A disadvantage of boom-sprinklers is that they are unstable and can tip over when being towed over rolling or steep topography.
- 163. SPRINKLER IRRIGATION 142 Traveling gunsrequire high operating pressure, 60 – 80 m. (6 - 8 bars) in the nozzle. The flow-rate of a single gun may be up to 250 m3 /h and the wetting diameter, up to 120 m. Application-rates vary from 7.5 to 25 mm/h. The water supply is carried out by means of a wide diameter, 4" – 6" semi-rigid round or flexible layflat hose. The hose is wrapped on a reel, mounted on a trailer. The gun can be pulled towards the trailer by the wrapping of the hose on the reel. There are two types of traveling guns: a. Hose-reel (hard-hose) system b. Cable-tow (hose-pull) system Either system is adaptable to various crop heights, variable travel speeds, water application amounts, odd shaped fields, and rolling terrain. The larger systems cover from 2 to 4 hectare per set. Fig. 12.15. Manually Moved Big Gun
- 164. SPRINKLER IRRIGATION 143 Fig. 12.16.Hose-reel Traveler Fig. 12.17. Cable Tow Traveler These systems require some labor in changing sets. One gun can cover up to 100 hectares in one cycle. This is the limit for maintaining a good soil moisture regime in a growing crop. The cable tow-system is usually cheaper than the hose-reel; it requires a wider alley to run in so the hose doesn't get kinked; the hose life may be shorter, and the cable
- 165. SPRINKLER IRRIGATION 144 pulls thesystem while the hose drags behind. The hose is usually rolled up mechanically at the end of a set before the system is moved. The cable-tow carries a 200 m. hose and the hard-hose up to 400 m. Both systems can water sets up to twice as long as the hose by turning the system around and pulling the hose back out. 12.4.4.2. Hose-reel Systems The hose-reel machine has a rain-gun mounted on a sledge or wheeled carriage. Water is supplied through a semi-rigid hose that is flexible enough to be wound onto a large reel. The 200 – 400 m long hose is used to pull the rain-gun toward the hose- reel. In a typical layout for a hose-reel system, the mainline is placed across the center of the field. The hose-reel is placed close to the mainline at the start of the first run and connected to the water supply hydrant. The rain-gun is slowly pulled out across the field by a tractor and the hose is allowed to uncoil from the reel. The pump is started and the valve coupler is opened slowly to start the irrigation. The rain-gun then is pulled back slowly across the field by winding the hose onto the hose-reel. Power to drive the hose-reel can be provided by a water motor or, more often, by an internal combustion engine. At the end of a run, the hose-reel automatically stops winding and shuts down the water supply. When the hose-reel is located in the center of the field, it is rotated 1800 and the rain-gun is pulled out in the opposite direction to start the next irrigation run. When irrigation is completed in this position, the hose-reel and the rain-gun are towed by tractor to the next outlet along the mainline. The hard-hose system is ready to move when it gets the hose reeled in at the end of a set. The hard-hose is easier to set up for a partial set than the cable-tow. Both systems require a moderate amount of labor, both are used particularly for irrigating crops growing on odd shaped or long, narrow fields. Fig. 12.18. Hose-reel Traveler Operating Scheme Adapted from Evans&Sneed
- 166. SPRINKLER IRRIGATION 145 12.4.4.3. Cable-towSystems The Cable-tow traveler has a rain-gun mounted on a wheeled carriage. Water is supplied through a flexible hose up to 200 m long and 100 mm in diameter, which is pulled along behind the machine. High flow-rates necessitates pipe of wider diameters, while low flow- rates allow the use of narrower diameters. The mainline is laid across the center of the field. A strip up to 400 m long can be irrigated at one setting of a 200 m long flexible hose. The rain-gun carriage is positioned at the start of its first run at a distance equal to one third of the wetting diameter from the field edge. The flexible hose is laid along the travel lane and connected to the rain-gun and the valve coupler on the mainline. A steel guide cable on the sprinkler carriage is pulled out to the other end of the field and firmly anchored. The valve coupler is opened slowly to start the irrigation. The rain-gun carriage is moved either by a “water motor” powered from the water supply using a piston or turbine drive, or, more often, by an internal combustion engine. At the end of a run, the carriage stops automatically and shuts- down the main water supply to the rain-gun. Labor is required only to reposition the hose, cable, and machine to start the next run. The traveling-gun is mounted on a self-powered chassis and travels along a straight line while watering. The common type of traveler gun sprinkler wets a diameter of more 120 m., in flow-rates of 35 – 120 m3 /h. The unit is often equipped with a water piston or turbine-powered winch that reels in the cable. The cable guides the unit along a path as it tows a flexible high-pressure lay-flat or round hose which is connected to a pressurized water supply system. The typical hose is often 4 inches (100 mm) in diameter and 200 m long, allowing the unit to travel up to 400 m. unattended. In some systems, after use, the hose can be drained, flattened, and wound onto a reel. In other cases, the plastic hose does not flatten when empty, and the reel assembly is parked at one end of the field and a tractor or truck pulls the gun- sprinkler carriage to the other end of the field, in a straight line. Then, the water is turned on and the reel slowly rotates, pulling the gun sprinkler in. When the carriage Fig. 12.19. Water Driven Cable-tow Traveler Scheme After D. Shoer 2011 Fig. 12.20. Cable-tow Traveler Operating Scheme Adapted from Evans&Sneed
- 167. SPRINKLER IRRIGATION 146 upon whichthe gun is mounted arrives at the reel assembly, a mechanism shuts off the system. The unit is moved to the next row and the process repeats until the entire field area is irrigated. The reel assembly rotates using an hydraulic motor which is driven by the water entering the unit, reducing the pressure substantially. The long hose causes significant pressure-losses. Thus, sufficient supply-line pressure is needed to operate such a system. The mainline or ditch for water supply has to be located at one end of the field, not in the middle of the field. The operator can use controls to adjust the rotation speed of the reel assembly and apply the desired depth of irrigation water. Some traveling sprinklers have a self-contained pump. mounted on the carriage that pumps water directly from an open ditch while moving. The supply ditches replace the hose. Travelers can also be equipped with boom-sprinklers instead of guns. Boom-sprinklers can be fixed or have rotating 18 – 36 m. long from which water is discharged through nozzles. As the traveler moves along its path, the sprinkler wets a strip of land 100 -120 m. wide rather than the circular area wetted by a stationary sprinkler. After the unit reaches the end of a travel path, it is moved and set up to water an adjacent strip of land. The overlap of adjacent strips depends on the distance between travel paths and on the diameter of the area wetted by the sprinkler. A part-circle sprinkler is frequently used, keeping the tow path dry for easier move of the unit. In a typical traveling sprinkler layout for a 32 ha field, the entire field is irrigated from eight tow paths, each 400 m. long, spaced 100 m. apart. Traveling sprinklers require the highest pressures of any system. In addition to the 4 – 7 bars required at the sprinkler nozzles, hose friction losses add another 1.5 – 2.5 bars to the required system pressure. Traveling sprinklers can be used in tall field crops such as corn and sugarcane and have even been used in orchards. They have the same advantages and disadvantages of gun and boom-sprinklers; however, because they are moving, traveling sprinklers have a higher uniformity and lower application-rate than stationary guns and booms. The application uniformity of travelers is only fair in the central portion of the field. Strips 30 – 60 m. wide along the ends and sides of the field are frequently poorly irrigated. The pressure at the rain-gun determines the application-rate. The forward speed of the machine controls the depth of water applied. Typical machine speeds vary from 10 to 50 m. per hour. The faster the machine travels, the smaller the depth of water applied 12.4.4.4. Friction-losses in Hose and Traveler Hose-fed traveling sprinklers use long (200 m), flexible, tough skinned hoses, that are capable of withstanding relatively high pressure. High-pressure traveler hoses are several times more expensive than pipes and often have a relatively short life- span due to physical damage and difficulty of repair. Furthermore, the end-pull required to drag a hose is approximately proportional to the square of the diameter. The requested hose diameter is determind by the hose discharge.
- 168. SPRINKLER IRRIGATION 147 The diameterof lay-flat hose increases by almost 10% under normal operating pressure. This gives the lay-flat hose about 20% more carrying capacity than the rigid plastic hose of the same diameter at the same friction loss gradient. As mentioned before, the traveler carriage can be powered by water turbines, water pistons, or engines. In determining system pressure requirements, the pressure head-loss and riser height of the traveler must be considered. This is especially important for turbine-driveen travelers when the pressure difference between the traveler inlet and sprinkler base typically exceeds 0.5 bars. Manufacturers provide friction-losses data for their travelers operation at various flow-rates and travel speeds. 12.5. Continuous-move Sprinkler Systems In addition to the before mentioned mobile irrigation systems, two systems, the Center-Pivot and the Linear-Move had been developed that irrigate while in move, contradicting to the tow-line, wheel-move and most of the gun-travelers that are moved from one position to another without irrigating and irrigation takes place while the system is in a stationary position. These systems are designated as irrigation- machines. In addition to frame, water delivery pipe and emitters, they are assembled of motors, gear drives, pumps, sensors, controllers and communication gear. 12.5.1. The Water Emitters Early mechanized systems were equipped with ordinary high-pressure impact sprinklers that threw the water for a long distance. In many cases, distribution uniformity was non-satisfactory, due to the long distance between the emitters and wind interference. Runoff from soil surface was triggered by the impact of the coarse water drops on the soil surface and in certain circumstances by high application- rates. Additional drawback of using these sprinklers was the high energy consumption. Requested operating pressure was 5 – 8 bars. In moving irrigation systems, in addition to the application-rate attribute, the parameter Specific Longitudinal Discharge (SLD), namely, the hourly flow-rate per length unit, along the moving lateral is very important. It facilitates the assessment of the performance, that is the maximum would-be irrigated area by the system. The Specific Longitudinal Flow-rate is the quotient of the system hourly flow-rate over the lateral length. Example: System flow-rate - 600 m3 /h, lateral length - 400 m. SLD = 600/400 = 1.5 m3 /m/h. The higher the SLD of the system, the more area the system can irrigate in a given time period, provided no runoff occurs. Table 12.1. Recommended Hose Size for Traveler Sprinklers FLOW-RATE INNER HOSE DIAMETER m3 /h Inch mm Up to 30 2.5 64 30 - 70 3.0 76 70 -120 4.0 102 120-150 4.5 114 150-250 5.0 127
- 169. SPRINKLER IRRIGATION 148 The commonSLD range is 0.5 - 2 m3 /h. Common advance velocity is 50 - 100 m/h. Although the specific longitudinal flow-rate of laterals with high-pressure sprinklers is high, the local application-rate can be lower than that of low and medium pressure systems that throw the water for shorter distance. Fig. 12.21. Linear-Move System with On-top High-pressure Impact Sprinklers and End-gun Water flow-rates of the sprinklers are determined by the size and shape of the nozzle on the sprinkler and the operating pressure,. Most sprinkler nozzles have water- passage of circular cross-section. Some sprinklers have straightening vanes, tapered or straight entrances, spreader vanes, or noncircular water-passage that extend or curtail the wetted diameter, change water distribution pattern, and determine droplet breakup and size distribution. Spreader nozzles or noncircular nozzles affect water droplet breakup and distribute the water more uniformly on the soil surface. Spreader nozzles are used to deliver water in the intermediate area between the impact arm splash and the external edge of the wetting pattern. For example, the large range nozzle on a certain impact sprinkler, throw the water 15 m. far away from the sprinkler if operated at 5 bars. The impact arm triggers splash that spread water in the range from 0 to 3 m. from the sprinkler. The distance between 3 and 15 m receives water in un-even distribution from the large nozzle. The spreader nozzle is added to equalize the water application pattern. Fig. 12.22. Impact Sprinkler – Nozzle Options Adapted from NebGuide
- 170. SPRINKLER IRRIGATION 149 The spreadernozzle has a narrower wetted diameter because of its smaller nozzle opening as well as since a portion of the water stream is broken into spray that wets the area between 3 and 9 m from the sprinkler. High-pressure impact sprinklers are recommended only in exceptional circumstances, such as the land application of wastewater, where large nozzles and high evaporation can be beneficial. Impact sprinklers are usually installed directly on the main lateral and discharge water upward at 150 to 270 angle. Undistorted wetting diameter is 15 - 30 m. Water application losses may be 25% and more. Low angle, 70 sprinklers reduce somewhat both water-loss and wetting diameter. End-guns have lower application and distribution efficiencies and high energy requirements, sometimes compelling the use of a dedicated booster pump. 12.5.1.1. Emergence of Low-pressure Emitters In due time a trend has emerged of using low-pressure emitters spaced more densely on the lateral. In the beginning, ordinary low-pressure emitters, used for micro-irrigation, sometimes with minor adjustments were used. Gradually it had been realized that continuous moving irrigating systems need distinctive emitters, matching with the unique operation requirements of the moving systems. Low-pressure emitters - static and dynamic sprayers, rotators and spinners were developed to be installed 1 - 4 m. apart along the lateral. The common emitter flow- rate is 1 - 5 m3 /h. The high-pressure impact sprinklers require operating pressure above 4 bars in the water inlet to the emitter. Medium-pressure emitters require 2 - 4 bars in water inlet. Low-pressure systems require 1 - 2.5 bars in the inlet. The working pressure of spray nozzles, rotators and spinners is 0.6 - 2 bars. Working pressure in LEPA (Low Energy Precision Application) emitters is 0.4 – 0.7 bar. The low-pressure systems have relatively high local application-rates that may cause runoff despite the little impact of the smaller water drops on the soil surface. Some definitions: a. Low-pressure emitter - water distributing device equipped with a nozzle and a stationary, rotating or oscillating deflection pad used to distribute water in 180 to 360 degree circles. b. Stationary pad - a deflection pad that does not move when impacted by the water stream leaving the nozzle. Water is ejected in spray pattern c. Rotating pad - a deflection pad that rotates in a 360 degrees circle when impacted by the water stream leaving the nozzle. Water is ejected as many distinctive streams. d. Oscillating pad - a deflection pad that oscillates when impacted by the water stream leaving the nozzle. The water is ejected in more uniform bigger drops with larger coverage area. e. Drop tubes -- plastic, rubber hose, or metal tubes used to deliver water to an emitter mounted below the pivot pipeline.
- 171. SPRINKLER IRRIGATION 150 f. Sprayers- In sprayers with stationary pad the water jet, ejected from the nozzle hits the deflector pad, from which the small water droplets are spread in a conic pattern. The wetting diameter is relatively small, 2 - 4 m. Spacing between the emitters on the lateral is 1 – 3 m. a. Spray Emitter b. Spray Emitter with Bubbler Clip c. Super-spray Fig. 12.23. Stationary Deflection Pad Emitters The spray head body provides a receptacle for the nozzle and positions the deflector plate in alignment with the nozzle, using 2 or 3 support bars. The circular-orifice nozzle is sized to discharge the designed flow-rate at the nominal pressure. Nozzle orifice diameters are usually sized in increments of 0.2 or 0.4 mm. Brass nozzles that were used in the past had been substituted with plastic nozzles that are color coded for ease of size distinction. The water jet impinges on the deflector plate, which is shaped to create the desired spray pattern and droplet sizes. A smooth deflector plate emits a thin sheet of water as it leaves the plate and creates the smallest average drop size at a given pressure and flow-rate. The smaller drops reduce soil impact energy, but are prone to excessive spray drift. This also decreases the wetted diameter. Serrated or grooved plates create many small jets and larger droplets. The fewer the grooves, the larger the jets and the larger the drops, the larger will be the wetting diameter. Fixed, grooved plates emit stationary jets which can severely impact the soil in localized areas when the lateral is stopped, due to the start- stop motion of most Center-Pivot laterals. Fixed groove plates have 15 to 30 grooves. This type of emitter is mostly mounted on top of the lateral, emitting the jets upward, that increase the wetted diameter while the canopy weaken the impact of the jets on the soil surface. Plates and nozzles can be changed easily without tools, allowing in-season conversion from an initial low-flow, small-drop package suitable for crop germination and establishment stages, to a full-flow, large- drop package for the peak water use period with full crop cover. Fig. 12.24. Nozzle and Deflection Pad Options for Stationary Spray Adapted from NebGuide
- 172. SPRINKLER IRRIGATION 151 The maindrawback of spray emitters is that the wetted diameter and thus the instantaneous application width are much smaller than with rotary sprinklers. This results in very high application-rates at the outmost end of the pivot lateral, up to 100 mm/h, which often exceeds the soil infiltration rate. To prevent surface-water runoff, special cultivation practices are requested, such as ridge tillage on row crops to preserves plant residue on the soil surface that improves infiltration and slows runoff. Reservoir tillage creates small basins that store water on the soil surface until it can infiltrate. 12.5.1.2. Dynamic Emitters In order to increase the wetting diameter with the micro-emitters, Dynamic micro- emitters had been developed. They have rotary deflection pads that significantly increase the wetting diameter, up to 15 meters and more, allowing a wider distance of 4 m. between the emitters on the lateral and reduce the application- rate. On drop tubes, facing downward, the rotator features the greatest throw distance available. The wide wetted diameter from rotating streams equates to lower average application-rates, longer soak time and reduced runoff. Shorter distance and more overlap of adjacent sprinklers improves uniformity but increases runoff hazard. Rotators are mounted on drop tubes, facing down or on top laterals and booms, where upright emitters are used. 12.5.1.2.1 Rotators The rotators Incorporate 4 or 6 groove plates. The bearings contain a viscous fluid to slow the rotation (1 – 2 RPM). The drops are relatively large, The 4 groove Rotator has the largest wetting diameter and biggest drops. Sensitivity to wind is low but the impact of the large drops on the soil surface and the high instantaneous application-rates due to the slowly rotating jets may increase runoff. 12.5.1.2.2. Spinners Spinners have similar plates but have a low friction bearing for higher speed rotation. Plate rotation takes place by the force of the water jets activated on the curved grooves. The rotation speed is affected by pressure and flow-rate. The spinner rotates much faster than the rotator, scattering smaller droplets. Its impact on the soil surface is slighter but the sensitivity to wind a. Super-spray Irrigating b. Rotator Irrigating Fig. 12.25. Micro-emitters On-drops in Work Fig. 12.26. Nozzle and Pad Options in Rotators Adapted from NebGuide Fig. 12.27. Up-right Spinner
- 173. SPRINKLER IRRIGATION 152 drift andevaporation is higher. The free spinning action generates a gentle, rain-like drops pattern. It is designed for relatively sensitive crops and soils, low instantaneous application-rates and reduced droplet kinetic energy help avoiding soil structure distruction and encrustation. 12.5.1.2.2.1. Convex plates are mounted upright on top of the lateral with higher trajectory angles, rendering larger wetting diameter and better uniformity of application-rates, but are more susceptible to wind drift. 12.5.1.2.2.2. Concave plates create jet trajectory angles of 60 – 350 . Usually the heads are inverted for use on drops. a. Upside-down Rotator b. Upright Rotator c. Upside-down Spinner 12.28. Rotators and Spinner 12.5.1.2.3. Accelerator That is an hybrid of rotator and spinner. It maximizes performance of in-canopy water application. by increasing rotation speed but keeping wide wetting diameter. a. Accelerator b. Orbitor c. Trashbuster 12.29. Distinctive Emitters
- 174. SPRINKLER IRRIGATION 153 12.5.1.2.4. Orbitor Manufacturedby Nelson, Features technology that eliminates the struts of the emitter's body, provides improved uniformity and optimal droplets at low pressure (0.7 – 1.5 bar). That keeps uniformity in poor water conditions, because there are no sprinkler body struts for debris to hang up on. The strutless body reduces droplet breakup, drift and drool. The streamlined design renders smooth movement through canopy and over field obstacles. The emitter is mounted on drop tubes and has low trajectory angles for keeping the water down, free of wind intervention, for maximum water and energy conservation. It is available with the choice of two plate types to meet desired droplet size, specific to site and soil requirements. 12.5.1.2.5. Trashbuster Manufactured by Nelson, features an open-architecture body design to pass debris more easily. This emitter had been developed for use with low-quality irrigation water, like reclaimed wastewater and stormwater. A clogging-resistant, flow-compensating sprinkler package can simplify system maintenance. 12.5.1.2.6. LDN (Low Drift Nozzle) Manufactured by Senninger, by using multiple deflector pad levels (single, double and triple), utilizes additional grooves to direct water and control droplet size. This enables the LDN to handle large flows, up to 3.8 m3 /h while still providing a gentle spread-out application. As the nozzle flow-rate has to increase with growing distance from the pivot point, multiple pads divide nozzle flow into a larger number of streams and apply that flow over a larger surface area, reducing application intensity and runoff hazard. The emitter operates at low pressure (0.4 – 1.4 bar). For LEPA the LDN offers a Bubble Pad for quick low-cost conversion to LEPA application. Discharging water near the soil surface minimizes evaporation and eliminates wind-drift. The bubble pad deposits water directly into the furrow basins and crop canopy is kept dry. a. Full-circle Emitter b. Part-circle Emitter Fig. 12.30. LDN Emitters at Work
- 175. SPRINKLER IRRIGATION 154 Part-Circle andChemigation pads are also available. The LDN-PC (Part-Circle) pad is designed to help manage difficult-to-irrigate areas especially near towers. IT distributes water away from wheel tracks and helps minimize mud creation. With a 170-degree spray pattern, the LDN-PC splits the water jet into 17 discreet streams at a 10-degree trajectory for minimum evaporative loss. Fig. 12.31. LDN (Low Drift Nozzle) Emitter Configurations The LDN emitters can be equipped with Chemigation Pads for upward spray under the crop canopy to wash the underside of a crop’s leaves where pests hide, eliminating or reducing the need for costly pesticides. Changing from irrigation to chemigation mode is done by twisting and unlocking the deflector pad. Then the pad is flipped over and twisted to lock it back in place. 12.5.1.2.7. Emitters with Oscillating Pads/Plates A new generation of dynamic emitters had been developed. That includes the Nutator made by Nelson and the Wobbler, made by Senninger. In these emitters, the deflection pad bends from side to side (oscillates like a pendulum) in addition to its rotary motion, improving uniformity of distribution. The angle of deflection determines the wetting diameter. The deflection angles vary from 100 to 450 . Oscillating plate emitters have some advantages over the fixed and rotating plate spray heads. They have a 6 to 9 groove plate in which the center of the plate moves in a circular motion around the water jet, and the entire jet is channeled through each groove in sequence. This ceates relatively large drops and a large wetting diameter. Trajectory angles are 150 or 250 . Fig. 12.32. Oscillating Deflection Pad Options Adaptee from NebGuide
- 176. SPRINKLER IRRIGATION 155 The emitterscan be mounted in upright positions above laterals or booms or inverted on drop tubes. Since the oscillation of the plate causes vibration, it should be suspended from a short length of flexible hose when mounted on drop tubes. a. Nutator b. Inverted Wobbler Fig. 12.33. Components of Oscillating Emitters Fig. 12.34. Inverted Wobbler on Drops Fig. 12.35. Diverse Configurations of Inverted Wobblers 12.5.1.2.8. Quad Spray The Quad-Spray had been developed particularly for LEPA irrigation. It has four different modes of water application. The Bubble and Aerated Bubble modes gently deposit water directly into furrow basins. The Spray Irrigation mode is used to wet the entire soil surface. This is desirable for seed germination, for some chemical applications and for irrigation of close seeded crops.
- 177. SPRINKLER IRRIGATION 156 The fourthmode is the Chemigation mode. This mode provides an upward spray that is very effective at washing away insects from the underside of the crop canopy. 12.5.2. Center-Pivots The Center-Pivot had been introduced in the early fifties in Colorado by Frank Zybach that later sold the patent to Valley (Valmont company). Fig. 12.37. Aerial View of Center-Pivot Irrigated Area Fig. 12.36. Quad-Spray and its Water Application Modes From Senninger Brochure
- 178. SPRINKLER IRRIGATION 157 In Center-PivotThe lateral rotates in a circle around a fixed point (pivot) like a clock hand. The pivot is connected to the water supply. Because of the circular movement, each emitter along the lateral covers a different area. Square plots are best suitable to Center-Pivots. The wetted area will be roughly 80% of the square. Wetting up to 95% of the square area is possible by the use of corner attachments. Fig. 12.38. Center-Pivot Operation Scheme Fig. 12.39. Net Irrigated Area The main adventages of Center-Pivot irrigation machines are: 1. Water delivery is simplified through the use of a stationary pivot point. 2. Guidance and alignment are controlled relative to the fixed pivot point. 3. Speed is set by the exterior tower of the base circle. 4. High water application uniformities are easily achieved with the moving emitters. 5. After completing one irrigation, the system is at the starting point for the next irrigation. 6. Irrigation management is improved by accurate and timely application of water. 7. Capability of accurate and timely applications of fertilizers in the irrigation water. These attributes diminish mechanical and operational problems associated with other types of self-propelled irrigation machines. Center-Pivots have two drawbacks: 1. Since the concentric band irrigated increases with each increment of radius, most of the water must be carried toward the end of the lateral, which results in high friction losses in the lateral. 2. When elevation differences between uphill and downhill lateral positions are significant, pressure regulation and or flow control nozzles have to be used to eliminate large variations in emitters discharge.
- 179. SPRINKLER IRRIGATION 158 Fig. 12.40.Components of Center-Pivot / Linear-Move Lateral System Source: Smith, A. In Industry & Investment NSW and CRC for Irrigation Futures Dual function systems were developed that can be used as Linear-Move or as Center-Pivot by changing the driving unit and the water inlet.
- 180. SPRINKLER IRRIGATION 159 Fig. 12.41.Universal System (Can Be Used as Linear-Move or Center-Pivot) Water is supplied to the Center-Pivot from a buried mainline or directly from a well located near the pivot point. Water flows through a swivel joint to the rotating lateral and emitters. When irrigating, the lateral rotates continuously around the pivot, wetting a circular area. One revolution can take from 20 to 100 hours depending on lateral length, the amount of water to be applied and the capacity of the water source. The slower the lateral rotates the more water is applied to the wetted area. Typical applied water depths vary from 5 to 30 mm. A Center-Pivot lateral can effectively apply light, frequent irrigations. The lateral consists of a series of spans with steel trusses, each is 25 - 75 m long and is carried about 2.5 - 5 m above the ground by drive units (“towers”). A drive unit consists of an “A-frame” supported on motor-driven wheels (commonly, 1 hp electric motor). The taller machines are used for orchard irrigation. Rubber tires, metal wheels, tracks or skids are mounted under each "A" frame to enable the machine travel. Most machines use rubber tires. High flotation tires used when needed. The outermost drive-unit moves continuously or intermittently to set the rotation speed, and all other drive-units move intermittently to maintain the lateral pipe in an approximately straight alignment. Speed of rotation of the machine is controlled from the main control panel in the pivot point. The most common Center-Pivot lateral is made of 6" pipe, approximately 400 m long. It irrigates a circular area of 50 hectares plus 1 – 3 hectares irrigated by the end sprinkler. Laterals 80 – 800 m. long are available for irrrigation of fields of different dimensions. In laterals longer than 400 m., one or more initial pipe spans have to be of 8" or 10" diameter. The guidance system is composed of appliances installed at each drive unit that keep the lateral aligned between the pivot and the end-drive unit.
- 181. SPRINKLER IRRIGATION 160 Fig. 12.42.Center-Pivot Main Tower Corner attachments, allow the corners of square fields and odd-ahaped areas of irregularly shaped fields to be irrigated. Fig. 12.43. Corner Arm The corner attachment is an additional tower that is operated only as needed. It swings out from the end of the lateral line to irrigate the corners or other odd shaped areas. Operation of the corner attachment is controlled by a signal sent through a buried electric cable. The corner arms have angle detectors for turning individualy, or in groups on and off the emitters as the arm swings out and back again. Some Center-Pivots have an end-gun that turns the water on in the corners. The machine can stop in the corner, the emitters along the lateral are closed by solenoid actuated valves. The end-gun irrigate for the pre-determing duraion, than it is closed
- 182. SPRINKLER IRRIGATION 161 and thesystem continues its regular operation. In some cases the lateral just slow- down in the corner and the end-gun is opened while the other sprinklers continue runing at lower flow-rates. The moving lateral pipeline is fitted with emitters to distribute the water evenly over the circular field. Because the lateral moves in a circle, uniform watering is achieved by linearly increasing the application-rate toward the outer end of the lateral. This is performed by varying either the nozzle size or the spacing of sprinklers. The area to be irrigated by each nozzle along the lateral becomes progressively larger toward the moving end, and the lateral speed becomes progressively faster. To provide uniform application, the sprinklers must be designed to have progressively greater discharges, closer spacing, or both, toward the moving end. The first option uses equally spaced sprinklers with small nozzles close to the pivot that gradually increase in size toward the outer end. The distance traveled by each emitter along a Center-Pivot lateral is equal to 2πr, where r is the distance of the sprinkler or spray nozzle along the lateral from the pivot point. The application-rate must increase with increasing r to obtain a uniform application depth. Since the lateral is traveling faster toward the end, also the “opportunity time” for application is reduced. The reduction is proportional to the speed of the lateral, which is proportional to the distance r from the pivot. If the same depth of water is requested all along the lateral, and because application depth equals the application-rate multiplied by opportunity time (i.e. mm/minute multiplied by minutes = mm), then as the travel speed increases toward the outer spans of the lateral, in even spaced emitters, the flow-rate has to gradually increase towards the lateral end. The second option employs emitters of the same flow-rate but they are placed closer together toward the outer end. This configuration simplifies maintenance since all the emitters are the same and require the same spare parts. In many cases, the application-rate near the moving end is 65 mm/h and higher. This may exceed the intake rate of many soil types except during the first few minutes at the beginning of each wetting event. To minimize runoff, the laterals are usually timed to rotate once every 12 to 96 hours depending on the soil's infiltration characteristics, the system's capacity, and the maximum allowed soil moisture deficit. Center-Pivot systems are suitable for almost all field crops but require areas free from any obstructions above ground such as telephone lines, electric power poles, buildings, and trees. They are best adapted for use on soils having high intake rates, Fig. 12.44. Options of Sprinkler Position and Dicharge Source: Howell USDA-ARS
- 183. SPRINKLER IRRIGATION 162 and onuniform topography. When used on soils with low intake rate and irregular topography, runoff can cause erosion and puddles that may interfere with the uniform movement of the lateral and traction of wheels Most pivot systems are permanently installed in a given field. However, in supplemental irrigation or for dual cropping, it may be practical to move a standard 400 m. Center-Pivot lateral back and forth between two 50-hectare fields Center-Pivots have safety switches to shut the system if any tower gets out of alignment. In uneven terrain, each sprinkler is mounted on a pressure regulator. Five types of power units are commonly used to drive the wheels of Center-Pivots: electric motors, hydraulic oil motors, water pistons, water spinners / turbines, and air pistons. The first pivots were powered by water pistons only. Today, electric motors are most common because of their speed, reliability, and capability to run forwards and backwards. Electric and hydraulic oil motors allow the system to be operated also while not irrigating ("dry operation"). In the last years, priority is given to electric drive machines, either 240 or 480 volt. 12.5.2.1. Electric-drive This drive requires three-phase power that can be provided directly by the electric supplier; from a single-phase power source through a phase converter or by an auxiliary generator. The electric drive system is easily reversed. It runs wet or dry, and there is a broad range of speeds available. The electric drive systems need skilled maintenance workers to deal with electrical problems when occur. The electric units are installed on low, medium or high pressure systems. The electric drive consumes approximately 75% less energy (depending on speed) than the hydraulic drives. Oil hydraulic pumping units have to provide a constant 120 bar operating pressure anytime, no matter what speed is employed. Electric drive machines provide power only when needed, thus reducing the overall energy costs. Electric motors of 0.5 - 1.5 horsepower are mounted on each tower with a drive shaft connecting the motor to a gear box on each wheel. 12.5.2.2 Oil-drive This apparatus utilizes an auxiliary hydraulic pump, connected to the pumping plant or running independently of the water supply pump. This enables operation of the system also when it is dry. The system works at high or low pressure. The oil hydraulic system suits to owner-operator service better than the electric system. Rotation speeds are adjustable to answer management objectives. 12.5.2.3. Water-drive No auxiliary power units are required since the energy is obtained from the pumped water for irrigation. Higher operating pressure than in other drives has to be maintained - 4 bars and higher, depending on the terrain. Water-drive units cannot be used with low pressure emitters without using pressure regulators for each emitter. Two types of units are available for a water drive system: the cylinder or piston and the spinner. This system cannot be moved dry. Reversing the system is possible with the spinner type but requires special adaptors for the cylinder or piston types.
- 184. SPRINKLER IRRIGATION 163 This unitis suitable to owner-operator service. Variable rotation times are standard and have to be adjusted to operation requirements. In hydraulic powered systems, speed control and tower alignment control are difficult. The system can be moved only when irrigating. Some Center-Pivots are designed to permit transfer from one pivot point to another. On these "towable" machines, the wheels at each tower can be rotated 900 to allow the machines to be towed from one or both ends. The towable units generally have aomewhat stronger construction with the towers closer together. Fig. 12.45. Towable Center-Pivot Center-Pivots are available in sizes from one tower, that irrigates 3 - 5 hectares in one circle rotation, to multiple tower machines capable of irrigating over 200 hectares. The single-tower machines are towable and designed to be used on multiple pivot points. Multiple-tower machines may also be towable, but there is a practical limit of approximately 60-hectares for a towable machine. Center-Pivots are available as low, medium and high pressure units, depending on the emitters' operating pressure. As mentioned before, the early pivots were high- pressure units with typical sprinkler operating pressures of 5 – 6 bars. Later, smaller rotary impact sprinklers were used of lower pressure of 2.5 – 4 bars, with a dedicated booster pump for the end-gun. Later on, low-pressure spray nozzles have been introduced which could operate at pressures as low as 0.7 - 1.0 bars. The major disadvantage of the low-pressure spray nozzles is a very high instantaneous water application-rate. The instantaneous application-rate is the rate of water application
- 185. SPRINKLER IRRIGATION 164 measured inmm per hour to a finite area of land as the machine moves across that area. High application-rates often cause runoff from many soil types (except extremely sandy soils). Most soil types have an intake rate less than 12 mm per hour. In extreme cicumstances, the instantaneous application-rate can reach 100 – 120 mm per hour. As a compromise between spray nozzle and conventional rotary impact sprinklers, some growers are using low pressure rotary impact sprinklers that operate at 2 bars pressure. The speed of rotation (time it takes to complete one revolution of the circle) of the system will depend upon the system size (length), pump capacity and the amount of water to be applied at each application. The time required to complete one revolution increases as the length of the system increases. A limited pump capacity or water supply can also increase the time needed to complete one revolution. As mentioned before, pivots are best adapted to flat terrain, but are being used satisfactorily on slopes up to 15%. Sloping terrain may require towers to be located closer together so that the lateral line can more closely follow the topography. In such slopes, pressure regulators are requested. Designing a Center-Pivot for a particular field is determined by the dimensions of the field. Initial map can be illustrated from an aerial photograph. Then a ground survey is conducted to decide on the exact pivot point location and to identify obstacles that have to be removed. Next, the water source capacity is determined. With this information, plus soil infiltration capacity, and peak daily evapotranspiration (ET) data, the system manufacturer uses a computer program to determine the lateral line size, emitter flow-rate and spacing, pump capacity and the required horsepower. The cost of 400 m long system is roughly $60,000. Additional $20,000 is needed if a corner arm is attached. The fixed costs for a Center-Pivot system depend on the area the system covers. The operating costs are about the same or lower than in other mechanized systems. The biggest savings are in man-power. Energy costs depend on the system attributes and the type of energy used. Maintenance and repair costs are higher than in other techniques since there are more mechanical parts than in the other systems. Total operating costs are competitive with the other types of movable sprinklers. 12.5.2.4. Nozzles High-pressure impact sprinklers generally operate at 5 – 6 bars. Impact sprinklers have a relatively large area of coverage, thus producing the lowest application-rates. Low-pressure sprinklers operate in the 1.5 – 3.5 bars range. The low-pressure sprinkler packages usually have a fairly high application-rate. When considering the use of low-pressure sprinklers, soil-intake rate, soil-moisture storage, crop water requirements, and elevation variability are important design factors. Low-pressure packages have the advantage of lower energy consumption. A large gun sprinkler can be used at the outer end to extend the effective irrigation range of the lateral. End-guns require a pressure of 3.5 – 7 bars, which often commits the use a booster pump mounted near the end-gun, when low-pressure spray or impact sprinklers are the standard emitters on the lateral. Sprinkler pressure changes that occur as a lateral rotates on a sloping field, cause flow-rate variations proportional to the square root of the operating pressure. Hence, water distribution uniformity from Center-Pivots with low-pressure sprinklers
- 186. SPRINKLER IRRIGATION 165 operating onuneven topography may be poor unless the sprinklers are fitted with flexible-orifice flow-control nozzles or pressure regulators. The designed Irrigation intervals and water application per revolution depend upon the rooting depth of the crop, the water holding capacity and the infiltration rate of the soil. Light, frequent irrigations maintain more uniform soil water levels but result in higher evaporation losses and greater wear on the pivot drive mechanisms. The infiltration capacity of the soil limits the allowed water application amount per pass. With electric drives, lateral speed can be set as a percentage of time. It is required because the constant-speed tower drive motors cycle on and off over short intervals to maintain the desired average speed. The on time for each tower varies with the distance from the pivot. Typical on/off cycle time length is 1 minute. The lateral is kept in alignment between the end tower and the pivot point by dedicated control devices activated by the deflections that are created by misalignment. When a tower falls behind, the deflections activate the drive motor until the tower catches up. One main advantage of this system is that it can be fully automated and controlled from a panel near the pivot or remotely from a nearby control center. Timers can be used to start and stop the machine and additional safety devices are used for shut-off the water. If the water pressure drops or one of the tower-drives breaks down, the system will automatically stop irrigating and an alarm will alert the operator. Several Center-Pivots covering large area can be easily controlled and maintained by a few people, particularly when automated remote monitoring and control are used. This allows easy scheduling and operation of irrigation, fertigation, and pesticide chemigation. Table 12.2. Characteristics and Performance of the Different Types of Emitters EMITTER TYPE SPACING CONFIGURATION PRESSURE RANGE - BARS WETTING DIAMETER - m Low-pressure spray Single-row drop 0.7 – 2.0 3 – 9 Single-row top 0.7 – 2.0 6 - 14 On short booms 0.7 – 1.4 12 - 18 On long booms 1.0 – 1.7 20 - 26 Low-pressure impact Variable spacing 1.4 – 2.4 18 – 23 Semi-uniform spacing 2.0 – 2.75 21 - 24 Medium-pressure impact Variable spacing 2.75 – 3.5 27 – 34 Semi-uniform spacing 2.75 – 3.8 30 – 37 High-pressure impact Uniform spacing 3.8 – 4.5 40 - 50 Center-Pivots operate best on sandy soils that infiltrate water quickly and can support the heavy wheel loads of the towers. Traction problems may occur when irrigating heavy soils, especially when laterals are equipped with micro-emitters of high application-rates. One acute trouble is the obligatory small application depths, which does not allow neither for replenish the soil water for deep-rooted crops nor for leaching of salts. Low-infiltration-rate soils limit the use of Center-Pivots equipped with high- application-rate micro-emitters. The use of Center-Pivots in medium to heavy soils in arid or semiarid areas is problematic. They should not be used in saline arid conditions.
- 187. SPRINKLER IRRIGATION 166 12.5.2.5. EmitterMounting Options Application modes for Center-Pivot may be of overhead (above-canopy) positions or near-canopy / in-canopy positions. The selected emitter type is determined by the desired mode of application. The mode and emitter type further affect the required spacing between emitters. The set of the above listed attributes is called “sprinkler package” because all aspects of design, installation, maintenance, and management affect the “package” performance. Sprays mounted on top of the lateral are prone to wind drift. In most cases, spray heads are mounted below the truss level, on a rigid pipe, connected to an 1800 gooseneck that is mounted on top of the lateral. Within corn crop canopy, flexible straight drops with spray heads are the preferred arrangement. Nowadays the low-pressure emitters are the favored choice in system packages. Field trials had proved that best application uniformity is achieved by drop-hanged emitters. Height above soil surface determines the drift and evaporation losses, as well as the impact on soil surface. When the emitters are spaced 1.5 – 2.0 m apart, nozzle operating pressure can be as low as 0.4 bars, but more emitters are required than with wider spacing of 4.5-9.0 m. Water application is most efficient when the emitters are positioned 40 – 45 cm above ground level, so that water is applied within the crop canopy. Spray, bubble or direct soil discharge modes can be applied. When there is no wind, low-pressure applicators positioned 1.5 – 2.0 m above ground can apply water with up to 90% efficiency. However, as the wind speed increases, the amount of water lost by evaporation increases significantly. Evaporation-loss is significantly influenced by wind speed, relative humidity and temperature. Wind speeds of 25 - 35 km/h; create evaporative losses of 17% - 30%. The overhead or over-canopy applicators are mounted on the Center-Pivot pipeline itself or on drops that are just below the truss rod elevation above ground. One of the main decision factors is whether overhead or over-canopy chemigation is desired. Impact sprinklers, spray heads, and rotators are suitable for this application mode. This application method is fitted to rolling topography, low intake soil types, and crops tolerant to overhead wetting. The near-canopy or in-canopy applicators are mounted on tubes dropped from the Center-Pivot main lateral. Emitters can be mounted near the ground (LEPA or LESA), within the crop canopy (LPIC), or just above the maximum height of the crop (MESA). Three types of low-pressure application modes can significantly reduce the requested operating pressure and water evaporative losses. 12.5.2.5.1. MESA (Mid Elevation Spray Application) Water applicators are located approximately midway between the main lateral and ground level. Water is applied above the crop canopy, even on tall crops such as corn and sugarcane. Rigid drops or flexible drop hoses are attached to the main lateral by means of gooseneck and extend down to the water applicator. Weights should be used in combination with flexible drop hose, to guarantee emitters stability. FIG. 12.46. Goosenecks on Top of lateral
- 188. SPRINKLER IRRIGATION 167 The requirednozzle pressure varies depending on the type of water applicator and pad pattern. Old applicators required 1.5 – 2 bar, while for the new generation, working pressure of 0.4 – 0.6 bar is sufficient in 2.5 – 3 m drop spacing. 12.5.2.5.2. LESA (Low Elevation Spray Application) The applicators are positioned 30 – 45 cm above ground level, or high enough to allow space for wheel tracking. Less crop foliage is wetted than in MESA position and less water is lost to evaporation. LESA applicators are installed 1.5 – 2.0 m apart, corresponding to the distance between two crop rows. Each applicator is attached to a flexible drop hose, which is connected to a gooseneck coming out from the mainline. Weights stabilize the applicators in wind conditions and allow the traveling through plants in straight crop rows. Nozzle pressure is as low as 0.4 bars. Water application efficiency averages 85% - 90%. In corn, water is sprayed underneath the primary foliage. In wheat, when plant foliage causes significantly uneven water distribution, the applicator is raised by swinging it over the truss rod. 12.5.2.5.3. LEPA (Low Energy Precision Application) Drop nozzles extend to within about 30 – 60 cm over soil surface. LEPA applicators are placed 1.5 – 2.0 m apart, corresponding to twice the row spacing. Thus, one interval between two rows is wet and one is dry. Dry soil allows more rainfall to be stored. The dry soil also improves the movement of the pivot wheels when the crop is planted in a circle. LEPA emitters can be operated in one of four modes: 12.5.2.5.3.1. Bubble Mode The overhead sprinklers are replaced with bubblers on drops closely spaced and the crop is precisely planted so that the rows follow the bubbler paths. The water is discharged between alternate crop rows. Water is applied from applicators positioned 30 – 45 cm above ground level that apply water in a “bubble” pattern. Pressure at the nozzle is 0.4 - 0.5 bar. A built-in pressure regulator is a part of the nozzle for compensation of elevation differences and friction head losses along the lateral. The inlet pressure to the pressure regulator should be above 0.7 bar. 12.5.2.5.3.2. Drag-Socks or Hoses Water is released directly to the ground. Socks reduce furrow erosion. Double-ended socks protect and maintain furrow dikes. This technique is used only for routine irrigation, not for germination and chemigation. The drag-sock and hose adapters can be replaced by a spray or chemigation pad when needed. Fig. 12.47. Positioning Options of Low-Pressure Emitters on Drops Source: Howell USDA-ARS
- 189. SPRINKLER IRRIGATION 168 12.5.2.5.3.3. HorizontalSpray Mode Most suitable for germination irrigation. Like the LEPA bubblers, sprayers are also positioned between alternate crop rows. The heads are higher off the ground than the bubblers, but still remain below the top of the crop canopy. The objective is to gain the advantages of LEPA systems with slightly lower instantaneous application- rates than with bubblers. Reservoir tillage usually is required. 12.5.2.5.3.4. Upward-Spray Mode Suitable for chemigation. 12.5.2.5.3.5. Advantages of the LEPA System a. Lower pressure requirements and the derived savings in energy costs. b. higher irrigation application efficiency due to decreased wind drift, higher distribution uniformity, and reduced wetting of the foliage. In LEPA, 95% - 98% of the irrigation water is applied to the active root-zone. Water application is precise and intense in limited soil surface. 12.5.2.5.3.6. Disadvantages of the LEPA System a. Higher equipment and installation costs b. saturated soil conditions and runoff that may occur without proper management c. more intensive maintenance is requested to repair and replace worn nozzles. d. Frequently, furrow diking - mechanical placement of small dikes down each furrow, is requested. e. For Center-Pivots, in certain circumstance, the field has be planted in a circled rows. Existing conventional Center-Pivot and Linear-Move machines can be converted to the LEPA system. Above-lateral sprinklers can be refitted to position the emitter heads under the lateral with lower pressure nozzle design. 12.5.2.5.6. LPIC (Low Pressure In Canopy) LPIC sprinkler systems offer a high efficiency alternative when LEPA and LESA specifications cannot be met. The land slope for a LPIC system should not exceed 3% on more than half of the field. Tillage and residue management techniques like furrow diking or pitting, in- furrow chiseling, or no-tillage management should be implemented to avoid runoff. On slopes steeper than 2%, terraces may be needed to prevent runoff and soil erosion. Center-Pivots equipped with LEPA applicators provide maximum water application efficiency at minimum operating pressure. LEPA can be used successfully in circles or in straight rows. It is particularly beneficial for low profile crops such as sugar-beet and peanuts. LESA Center-Pivots can be converted easily to LEPA with an applicator adapter that includes a connection to attached drag sock or hose. Fig. 12.48. Furrow Dikes
- 190. SPRINKLER IRRIGATION 169 In cornproduction, 10% - 12% of the water applied by above-canopy irrigation is lost by wetting the foliage. There is 20% - 25% more water loss from MESA above-crop- canopy irrigation than from LESA and LEPA within-crop-canopy Center-Pivot systems. 12.5.2.6. Use of Offset Booms In heavy soils with low water intake rate, the use of spray booms, each one equipped with 3 - 7 low volume sprayers as a replacement for each sprinkler, can reduce runoff and water losses significantly. One of the challenges in using low pressure spray devices is to spread the water across a wider area to reduce the intensity of the application-rate. Today, “boom drops” (also referred to as “offset booms” or “boom backs”) are used to broaden the width of coverage. Boom drops are created by angling a normal drop tube away from the lateral pipe at approximately 450 angles both fore and aft of the lateral. Only one nozzle is placed at the end of each boom drop. The placement of boom drops fore and aft of the Center-Pivot lateral takes place in an alternating manner. The drop conduit may be reinforced and held in place by a small truss system that extends down from the lateral pipe. In other configurations, drop tubing may be suspended over lateral truss rods, except near drive towers, and held in place by clips. Boom drops are relatively inexpensive and are effective in reducing the intensity of water application. Boom drops are used if there is a need to spread water further from the Center-Pivot. Sometimes they are used on the outlets closest to towers so that the majority of soil wetting takes place behind the wheels. A part circle spinner type of nozzle suspended below the Center-Pivot provides better control of wheel slippage than an aft-oriented boom back having a full circle nozzle. Generally, boom drops are used only on the outer segments of the Center- Pivot lateral where the application- rates are more intense. Since sprays have relatively small wetting diameter and consequently high local application-rates, offset booms are used to increase the overall spray wetting width. Offset pipes up to 6 m in length are used with 20 - 25 mm steel tubing. The simplest structure has support braces attached to the truss rods of the lateral span. A swivel joint is used to connect the combined spray head-regulator unit. Adjustable boom system uses a clamp on the lateral pipe to support the offset, independently of the truss rods, and the angle can be easily adjusted. A short 20 mm hose delivers the water from a lateral outlet to the boom. The booms can be mounted anywhere along the lateral with fixed or variable spacing, and alternated on either Fig. 12.49. Boom-backs behind Center-Pivot Towers
- 191. SPRINKLER IRRIGATION 170 side ofthe lateral. They are often used adjacent to pivot towers to apply most of the water behind the wheels to minimize soil compacting. The adjustable boom allows changing the elevation of the spray head either within season as the crop height increases, or between seasons when different crops are rotated. A minimum crop clearance of about 1.0 m is recommended for high application uniformity. Offset booms allow use of spray heads of smaller wetting diameter, and lower pressure, facilitating minimizing the elevation of the spray above the surface, and peak application-rates. Such a system increases equipment costs, weight on the span and wheels and susceptibility to wind damage. Fig. 12.50. Bi-lateral Boom Appendage with End-gun on a Center-Pivot 12.5.2.7. Pattern (Wetting Diameter) Size and Uniformity Uniformity is affected by the size and shape of the water spreading pattern and the spacing between nozzles. The pattern in turn is affected by nozzle size and pressure, type of emitter deflector / plate and elevation of the emitter head.
- 192. SPRINKLER IRRIGATION 171 Table 12.3.Wetting Diameter of Emitters at 1.8 m3/h Flow-rate EMITTER PLATE THROW ANGLE PRESSURE - BAR DIAMETER – m 1 m HEIGHT DIAMETER – m 2 m HEIGHT Fixed Plate Smooth 00 1 7 9 Fixed Plate Serrated 00 1 9 11 Rotator 4 Groove 80 2 17 19 Rotator 6 Groove 120 1 13 15 Nutator 7 Groove 120 1 13 14 Nutator 9 Groove 210 1 14 15 Rotator 6 Groove 120 2 15 17 Spinner 6 Groove 120 1 12 13 Spinner 6 Groove 350 1 15 16 Wobbler Standard 250 1 14 15 Wobbler Standard 250 2 16 17 Wobbler Low Angle 150 1 13 14 Wobbler Low Angle 150 2 14 15 I-Wobb Standard 200 1 14 16 I-Wobb Low Angle 150 1 14 15 After King and Kincaid (1997) Table 12.3. presents the wetting diameters of different emitter head and deflector / plate combinations at operating pressures, nozzle heights and flow-rates which are typical for the outer span of a pivot lateral. Higher trajectory angle and nozzle pressure render a larger and more uniform wetting pattern. The oscillating emitters create a more uniform application-rate than fixed- plate or low-angle rotating plates. High uniformity (CU>95%) is obtained if spacing does not exceed 25% of the wetting diameter. That is particularly important in the outer spans of the Center-Pivot where flow requirements per unit length of lateral are high, and smaller nozzle sizes and drop sizes are desirable. Uniformity problems may occur near the pivot point where flow requirements are smaller. 12.5.2.8. Application-rates Average application-rates of a certain flow-rate of emitter are inversely proportional to the diameter of its wetting pattern. Peak application-rates are 1.3 to 1.5 times the average rate. Thus, there is a difference of 1:3 in application-rate between the smallest and largest wetting pattern emitters. Using alternating 4 m offset booms can decrease the application-rates from fixed plate sprays by a factor of 2, and from the larger wetting patterns by a factor of about 1.5. Since the application-rates under the outer spans of most pivots exceed the infiltration rate of all but sandy soils, the use of offsets is mostly justified on the outer one-third of the lateral. Reducing application-rates allows larger water application depths and longer intervals between applications that reduces surface evaporation and disease infection. 12.5.2.9. Droplet Size Droplet sizes are an important factor in selection of a sprinkler package. Droplet size distribution and droplet kinetic energy can be determined for most types of emitters given the data of nozzle and spray plate type, nozzle size and pressure. The operating pressure determines the wetted diameter and mean water droplet size.
- 193. SPRINKLER IRRIGATION 172 As pressureincreases, the mean drop size decreases. If emitters are operated at design pressure, water droplets are segregated within the wetting pattern. Larger droplets tend to reach the outside edge of the pattern due to their bigger mass and velocity when leaving the nozzle. Only a small fraction of water droplets at the outside edge of the wetting pattern can be categorized as small water droplets while the inner portion of the pattern is dominated by smaller water droplets. If the emitter pressure is too high, the normal distribution of water droplet sizes is distorted, and a nearly uniform smaller water droplet size results. In this case, the energy contained in the water as it leaves the nozzle is excessive, causing immediate water droplet breakup and small water droplets to dominate the pattern. Small water droplets do not have enough mass to reach great distance from the emitter. This means that an emitter operating above the design pressure can have smaller wetted diameter than the same nozzle operated at the design pressure. Emitters operating well below the design pressure produce many large water droplets. The energy contained in the water as it exits the nozzle is low and only minimal water droplet breakup occurs. The lower energy also reduces the distance that droplets reach from the emitter, despite their bigger size. With too low pressure, the water distribution pattern is characterized by large water droplets and a reduced wetted diameter. In a certain type of emitter and plate, drop sizes increase as nozzle size increases or nozzle pressure decreases. Mean volumetric drop size ranges from 1 mm for the smooth plate spray to 2.5 mm for the 4-groove Rotator and Wobbler at low pressure. Droplet kinetic energy per unit volume of water applied increases fivefold from the smooth plate to the Rotator. On silt-loam and loam soils, as drop energy flux increases, the infiltrated depth prior to runoff decreases by a factor of 2 or 3. When selecting drop sizes in spray package, the potential of spray drift-losses has to be weighted against the potential for soil surface sealing and runoff. 12.5.2.10. Water Trajectory Water leaving a sprinkler or spray nozzle exits at an angle relative to the horizon. The path taken by water on its way to the soil surface is referred to as its trajectory. Gravity forces the water droplets downwards to the soil surface. If the stream is directed slightly upward from horizontal, it will reach farther from the nozzle unless the trajectory is diverted by wind wind. Impact sprinklers and spray nozzle packages may distribute water at a variety of angles. By directing the water slightly upward, concave pads have a wider wetted diameter than the flat or convex (downward oriented) pads.
- 194. SPRINKLER IRRIGATION 173 12.5.2.11. Sprinkler-packages Fig.12.51. Emitter Spacing Patterns in Center-Pivot Adapted from Valmont Brochure Due to the complexity of the Continuous-Move Sprinkler Systems, most of the dealers and equipment manufacturers offer farmers their assistance in fitting the ordered equipment to the local conditions and requirements. They advise in choosing the suitable Sprinkler-package. The sprinkler-package is a combination of the applicator, the application mode, and the spacing between applicators. The system capacity determines the peak application-rate of the particular sprinkler application package. The sprinkler-package should be suitable to the tillage and the agronomic system of the operator. The particular soil and slope conditions define the infiltration rate and runoff hazard. The intersection area between the infiltration curve and the application-rate curve illustrates the potential runoff or surface water redistribution that may require surface storage of basins or reservoir tillage needed to reduce or eliminate runoff from LESA, LESA, or LPIC systems.
- 195. SPRINKLER IRRIGATION 174 Fig. 12.52.An Example of Water Logging by Spray Emitters - Close-up 12.5.2.12. Operating Pressure Each emitter is designed to operate within a range of water pressures. Typically, impact sprinklers can be operated over a wider range of pressures than low pressure spray nozzles. A high pressure impact sprinkler can be operated in a pressure range from 2.5 to 5.5 bar while an oscillating low pressure spray nozzle would be suited to pressures between 0.7 and 2.5 bar 12.5.2.13. Maintaining Adequate Pressure Pressure losses and head fluctuations may decrease the efficiency of irrigation in mechanized systems. Excess pressure can accelerate the wearing-out of the nozzles and the deflection pads. Some equipment manufacturers stipulate warranty on the installation of pressure regulators prior to the emitters. In plots with significant topographic variance, diversity in pressure renders variability in the flow-rate of the emitters and the use of pressure or flow regulators is necessary. The use of pressure and flow regulators requires routine calibration of the combined regulator-emitter unit, in the beginning of the irrigation season. Pressure-loss in the regulators is 3 – 7 m. (0.3 - 0.7 bar), depending on the flow-rate of the emitter. These data have to be taken in account in designing the pressure requested in the water inlet. a. Uneven Water Distribution from Low-Pressure Emitters on Slopy Terrain b. Use of Pressure Regulators Facilitates Uniform Water Distribution Fig. 12.53. The Effect of Using Pressure Regulators in Slopy Terrain From Senninger Brochure
- 196. SPRINKLER IRRIGATION 175 A pressureregulator confines excess inlet water pressure to a constant outlet pressure. Constant outlet pressure is needed to ensure the adequate performance of the emitter. a. Standard PR b. PRLV c. Upside-down Flow d. Cross Section Fig. 12.54. Small Diameter Pressure Regulators Installed for Single Emitters and on Drops 12.5.2.13.1. The Working-pattern of Pressure Regulators The water flows through the inlet of the regulator and around a fixed seat into the critical flow area. The water then enters into a hollow cylinder called a throttling stem (or T-stem) which is attached to a larger diaphragm near the outlet end. A spring around the throttling stem holds the flow area open, while water pressure acting on the total diaphragm area tries to close it. This duel always ends in a draw with the outlet (or regulated) pressure being determined by the spring’s compressive strength. There are two types of pressure regulator (PR): Standard PR and Pressure Regulating Limit Valve (PRLV). Both maintain a constant outlet pressure when handling rated flows. The difference comes when there is no flow through the device. The standard pressure regulator will read the same pressure in and out when there is no flow. The limiting valve (PRLV) has a rubber seat and therefore is able to limit the downstream pressure to about 7 – 10 m. (0.7 – 1.0 bar) above the rated outlet pressure, even with no flow conditions. This helps to guarantee optimum system performance and protects downstream components. Both operate with very low hysteresis, though the limiting valve has slightly more friction loss at the same flows. A standard pressure regulator must be installed downstream from all shut-off valves. A pressure regulating limit valve (PRLV), with its different internal construction, can be installed also upstream of shut-off valves. With either device, use of a filter upstream is recommended - 100 mesh or finer. capable of flowing up to 4.5 m3 /h with no more than 3 m. (0.3 bar) internal friction loss. On flat land. the pressure can be regulated in the water inlet instead of in single emitters. It is much cheaper and maintenance is simpler. Center-Pivot and Linear-Move towers interfere with the distribution of water from the adjacent emitters. Reduction in this interference can be achieved by the replacement of each emitter above the tower with two part-circle emitters that throw the water to
- 197. SPRINKLER IRRIGATION 176 both sidesof the wheel. This adjustment renders one more advantage: the wheels advance on dry soil layer without compacting the soil. Some of the units are equipped with built-in automatic filters. This arrangement is particularly essential when water pumping is done directly from a ditch in the field. Linear-Move and Center-Pivot systems can be used for chemigation. In the past, the insecticides were applied through the irrigation system. Nowadays, it is preferred to mount a distinct spraying booms, using the irrigation system only as a conveyor. 12.5.2.14. Emitter-Nozzle Configuration When using impact sprinklers, for simplicity of manufacture and ease of field assembly, uniform spacing between outlets is the most commonly arrangement. However, in this configuration, relatively large nozzles and high pressures are required. The high pressures result in high energy costs, and on fine-texture soils without plant or plant residues cover, the large droplets from the large nozzles may cause encrustation of the soil surface. To avoid the problems associated with the use of large nozzles, combination spacing is often used. A typical combination spacing strategy is to use a 12 m. sprinkler spacing along the first third of the lateral, a 6 m. spacing along the middle third and a 3 m. spacing along the last third of the lateral. Thus, the outlets can be uniformly spaced at 3 m. intervals along the lateral. To vary the sprinkler spacing, some of the outlets are closed with plugs. Thus, sprinklers are installed in every fourth outlet along the first third of the lateral, every other outlet along the middle third, and every outlet along the last third of the lateral. The methodology of selecting the nozzle sizes along a Center-Pivot lateral: 1. Determining the discharge required from each emitter to apply a uniform application of water throughout the irrigated area. 2. Determining the pressure available at each sprinkler outlet, starting with a design pressure at the end. 3. Selecting the appropriate nozzle size conforming with the required discharge and the available pressure. 12.5.2.15. Emitter Flow-rate The sprinkler or nozzle flow-rate required at any outlet along a Center-Pivot lateral can be computed by (Eq. 12.1) Where: qr is the emitter flow-rate required at r – l/s; Figure 12.55. Relationship between Width of the Wetted Coverage (W) and Application Intensity for the Same Flow-rate
- 198. SPRINKLER IRRIGATION 177 r isthe radius (distance) from pivot to outlet – m.; Sr is the sprinkler spacing at r (which is equal to half the distance to the next upstream sprinkler plus half the distance to the next downstream sprinkler) – m.; Q is the system capacity – l/s; and, R is the maximum radius effectively irrigated by the Center-Pivot – m. Generally, higher pressure is required by sprinkler or spray emitters with larger wetted diameters. Given the same flow-rate per nozzle, a nozzle that has the smallest diameter of wetted coverage (W) will have the largest application-rate and intensity. The smaller diameters of coverage will be more prone to runoff. This should be a major consideration in the selection of the type and working pressure of the spray or impact device. Figure 12.56 presents a way of looking at the relationship between time of wetting and required application-rate (intensity) for a given water application depth. This figure shows that as the time of application is shortened by using nozzles of smaller wetted diameter, the application intensity is increased for the same depth of water application. Where soil sealing and infiltration rate are likely to be problems, relatively low pressure can be used to save energy. In soils that are more difficult to manage, higher pressure should be used. On undulating topography, where pressure vary because of elevation changes, flexible orifice nozzles on impact sprinklers and pressure regulators on drops can be used to maintain the desired flow-rate. 12.5.2.16. Emitter Height Above the Ground As mentioned before, Higher heights of emitters provide larger wetting diameter for the same nozzle type and size. In this case, the overlapping percentage is increased and the uniformity of water application along the lateral is improved. Data and guidelines are available from manufacturers. Table 12.4. shows the maximum nozzle spacing allowed for low pressure spray devices for a 6-ft height. This table provides an indication of the impact of nozzle. Table 12.4. Recommended Spacing – m. for Emitters at 2 m. Height at Different Working Pressures (adapted from Kincaid, 1996, Irrigation Bus. Tech.). PRESSURE – BARSTYPE OF SPRAY DEVICE 0.7 1.0 1.5 2.0 Fixed plate sprays 2 2.5 2.5 3 Rotator – 4 groove 2.5 3 3.5 4 Rotator – 6 groove 2.5 3 3.5 4 Wobbler – low angle 3.5 4 4 4.5 Wobbler – high angle 4 4.5 4.5 5 Figure 12.56. Relationship between the Required Application Intensity and Time of Application for the Same Depth of Application
- 199. SPRINKLER IRRIGATION 178 12.4.2.17. Time-lengthof Wetting Calculating the minutes of wetting time at various locations along the lateral: The wetting time at any radius r from the pivot point can be calculated as: (Eq. 12.2) Where: twet is the time that any point on the soil surface at radius r gets wet (minutes); w is the wetted radius - m. 12.5.2.18. End-gun and Corner-system Operation In the past, when energy costs were low, end-guns were commonly used to extend the length of Center-Pivots coverage. since the 1990’s, energy costs bounced, and the annual cost of ownership for an additional span of lateral pipe is lower than the costs for the energy requested to pressurize and operate the end-gun. End-guns became less common for extending the base circular area. They are, however, still used to increase the irrigated areas of field corners. When land price is high, corners of fields are generally irrigated. In areas where land is plentiful and water supply is limited, field corners are left unirrigated. End-gun pressures should be at least 35 – 45 m. (3.5 – 4.5 bar) and higher. Often, low pressure systems that use spray, spinner or rotator nozzles require booster pumps to create sufficient pressure to operate the end-gun. The booster pump is mounted on or next to the last drive unit. In medium and high-pressure sprinkler laterals, a booster pump may not be required. Intermittently operated end-guns and/or corner-systems on Center-Pivot laterals require the use of pressure regulators on all the emitters. When the end-gun and/or corner-system are turned on, the pressure along the lateral decreases due to increased friction. Figure 12.57. Center-Pivot End-gun Installations where the Pump, Valve, and End-gun are Shortcoupled at the End of the Lateral (left side), and an End-gun on a Corner-system (right side).
- 200. SPRINKLER IRRIGATION 179 The highapplication intensity of big-guns, the large drop size and velocities can cause encrustation of the soil surface that reduce the infiltration rate and increase runoff. Sizing of the end-gun is determined by the manufacturer as a part of the specifications of the sprinkler package. The following equation can be used as a check on manufacturer calculations. The radius, R, of the irrigated area created by a Center-Pivot system with an end-gun operating can be calculated as: (Eq. 12.3) Where: Rg is the radius of throw – m. of the end-gun. Rg is defined by the manufacturer as the maximum throw under low wind conditions, the outer 25% of this radius may not have sufficient water application to satisfy the crop, so it may not even be planted. Therefore, the 0.75 reducing coefficient is applied. Values for Rg change with pressure and nozzle size and are available from sprinkler manufacturers. With corner-systems, the maximum radius R of the irrigated area is: (Eq. 12.4) Where: L is the length of the standard base lateral from the pivot point to the end. Rc is the length of the corner system – m, when fully extended. Usually remains an angle, smaller than 1800 between the corner system and the base lateral, even when the corner system is fully extended. For corner systems having end-guns, the maximum radius, R, of the irrigated area is (Eq. 12.5) 12.5.2.19. Orchard Irrigation Although in very limited scale, Center-Pivots are used for orchard irrigation. Two prereqisits are indispensable: a. Overhead b. Under-canopy on Drops Fig. 12.58. Irrigation of Orchards by Center-Pivot a. Planting in circles.
- 201. SPRINKLER IRRIGATION 180 b. Limitingcanopy height by hedging, when necessary. That technology corresponds with the new trends of dense planting and limiting tree size for saving labor in harvest and introduction of mechanical harvest in certain crops. Water application may be overhead by impact sprinklers, rotators or wobblers or under-canopy by sprayers on drops 12.5.2.20. CALCULATIONS (Adapted from Nelsom Pivot Pocket Guide) AREA IRRIGATED BY CENTER-PIVOT (Assumes end-gun on all the time.) A = area (ha) Lp = pivot length (m) Rg= end-gun radius (m) Example: the area irrigated by a 400 m long Center-Pivot with an end-gun radius of 40m. = 60.8 ha HOURS PER PIVOT REVOLUTION @ 100% TIMER. (Eq. 12.7) Tr = hours per revolution (hr.) Lt = distance to last tower (m) Vt = last tower speed (m/min.) Example: The time needed for the center-Pivot above to complete a revolution at the maximum tower speed of 3m/min. (100% timer). The machine includes a 15m overhang. Tr = 13.5 hours per revolution DEPTH OF WATER APPLIED BY A CENTER-PIVOT. (Eq. 12.8) D = depth of water applied (mm) Qp= pivot flow-rate (m3 /hr) Tr = hours per revolution (hrs.) Lp = pivot length (m) Rg= end-gun radius (m) Example: Depth of water applied by the above pivot. Flow-rate is 240 m3 /hr. Last tower speed is 0.75 m/min (25% timer). D = 21.3 mm (Eq. 12.6)
- 202. SPRINKLER IRRIGATION 181 REQUIRED FLOWFOR A GIVEN CENTER-PIVOT SPRINKLER (Eq. 12.9) Qe= sprinkler flow-rate (lpm) Ls = distance to sprinkler (m) Qp= Center-Pivot flow-rate (m3 /hr) Le = sprinkler spacing (m) Lp = length of lateral (m) Rg = end-gun wetting radius (m) Example: The flow-rate required by a sprinkler located 250m from the pivot point, if the Sprinkler spacing is 5m. Center-Pivot flow-rate is 240 m3 /h. Qe = 51.8 lpm = 3.1 m3 /h AVERAGE APPLICATION-RATE (Eq. 12.10) Ia = average application-rate (mm/hr.) Ls = distance to sprinkler (m) Qp= Center-Pivot flow-rate (m3 /hr) Lp = length of lateral (m) Rg = end-gun wetting radius (m) Ld = sprinkler throw diameter (m) Example: The average application-rate at the distance of 250 m from the pivot point. System flow-rate is 240 m3 /hr and sprinkler coverage diameter is 18 m. Ia = 34.4 mm/h REQUIRED SYSTEM FLOW (Eq. 12.11) Qs = system flow-rate (m3 /hr/ha) ETp = peak evapo-transpiration (mm/day) Tp = pumping hours per day Ea = water application efficiency (decimal) Example: The required system flow-rate when the peak crop water requirement is 8 mm/day, water application efficiency is 90% and the system can be operated 18 hours per day. Qs = 4.9 m3 /hr/ha
- 203. SPRINKLER IRRIGATION 182 POWER REQUIRED(kW) (Eq. 12.12) P = power (kW) Qp = system flow-rate (m3 /hr) H = head that the pump has to generate (m) Ep = pump efficiency (decimal) Example: The power required to pump 240 m3 /hr against a head of 60 m. Pump efficiency is 75% P = 52.3 kW NOZZLE OR NON-REGULATED SYSTEM FLOW-RATE WITH CHANGING PRESSURE (Eq. 12.13) Q1 = flow to determine (lpm) Q2 = known flow (lpm) P1 = pressure (bar) for Q1 P2 = pressure (bar) for Q2 Example: Determination of the flow-rate of a #30 3TN nozzle at 1 bar, knowing the flow-rate at 0.7 bar is 18.7 lpm. Q1 = 22.35 lpm 12.5.3. Linear-Move Systems Fig. 12.59. Linear-Move Lateral 12.5.3.1. Overview The basic Linear-Move construction is similar to that of the Center-Pivot. it combines the structure and guidance system of a Center-Pivot lateral with a traveling water
- 204. SPRINKLER IRRIGATION 183 feed systemsimilar to that of a traveling sprinkler. Instead of moving in a circle, the linear system moves as aligned straight line through the field, generally at right angles to the row direction. Instead of a pivot point that is anchored while the machine rotates around it, there is a chief tower that controls the remainder of the machine. The Linear-Move is constructed from a wide diameter 6" – 8" galvanized steel pipe, 200 - 400 m. long, mounted on wheeled mobile towers. Pipe diameter depends upon the system capacity and lateral length. The towers are spaced 30 – 60 m. apart. Water feeding can be done in the center of the lateral or in one of its edges. A center-feed system can use smaller diameter lateral pipe than an end-feed system of the same capacity and length, due to the lower friction loss, since water is being distributed in two directions, one half of the flow-rate to each side of the lateral. Each tower has an electric motor and is guided indepentently by cables and micro-switches to keep the lateral aligned. The alignment is monitored through switches in contact with a straight cable along the center or the end of the field. At the main tower are installed the pump and power unit, plus a generator to provide power for the electric motors. Old models were driven by water pressure. Today, most systems are driven by electric motors. The advantages of electric drive is that it is independent of the water pressure state and the machine can be moved across the field dry, without applying water, when returned to the starting point. The system is driven either by the water pressure, diesel or electric engine. As mentioned before, the water inlet is located at the pipe edge or in its center. The water is supplied from hydrants in the field by connecting and disconnecting a wide diameter, flexible hose; by a dragged long flexible hose or pumped directly from a canal along the field border or in its middle. The water dosage depends on the traveling speed of the lateral, the intake rate of the soil and the flow-rate of the emitters. The length of the irrigated field may be up to 1000 - 2000 m. At the end of the field the lateral can be rotated 1800 and returned in an adjacent trail. The design of Linear-Move systems is prepared by the manufacturer or dealer by- means computer software. The pipe is sized to minimize friction losses. Linear-Move laterals are equipped with spray nozzles or impact sprinklers, as the Center-Pivot. The emitters are installed at uniform spacing and should have the same characteristics all along the lateral. Water application depth varies with the lateral speed. The system can be automated in the same way as the Center-Pivot. Fig. 12.60. On-lateral Trip Switch
- 205. SPRINKLER IRRIGATION 184 Fig. 12.61.Linear-Move System with Spray Emitters on Drops The Linear-Move machine is designed to be used on rectangular fields. An ideal field layout allows a travel distance which is two to three times the length of the lateral. Shorter travel distances will increase the cost of ownership of the machine, economically feasible only for high value cash-crops. Since most of these machines are operated in low to medium pressure, they are best suited to fields with little elevation differences. The low-pressure machines use spray nozzles that have a high instantaneous application-rate, suitable to high infiltration- rate soils only. The medium-pressure machines use low-pressure impact sprinklers, have a lower instantaneous application-rate, and can be used on soils that have a moderate infiltration-rate.
- 206. SPRINKLER IRRIGATION 185 Fig. 12.62.Linear-Move System with Rotators on Drops Some Linear-Move systems are getting water from hydrants by a flexible hose so that some undulation in ground elevation is allowed. From the hydrants the water is delivered through 100 - 200 m. segments of high pressure, flexible, rubber coated, synthetic textile hose to the main tower of the machine. Moving the hose each time that the machine travels 200 to 300 m. is time consuming, requires a tractor and two workers. More sophisticated systems utilize automated coupling mechanisms in which the water is supplied from evenly-spaced hydrant valves along a buried mainline pipe. The automated coupling systems use swing-arms with swivel joints to connect to the hydrants as the system moves down the field, and they are suitable for application in undulating topographies, but they are much more expensive than Linear-Move systems that take water from a ditch or a flexible hose. Hose-pull systems generally obtain necessary water pressure from the water source. An auxiliary electrical cable is often used to provide power for towers' drives.
- 207. SPRINKLER IRRIGATION 186 Some systemsuse GPS technology in guiding the Linear movement. As mentioned before, Linear-Move systems can pump water from open ditches. The ditch-fed machines are esaier to operate and require less labor. The slope on the canal should not exceed 1%. Water control structures are needed to insure adequate depth of water in the canal. At each water control structure, it is necessary to manually lift the suction hose across the structure. A large self-cleaning screen is mounted on the suction hose to prevent clogging of emitters. Fig. 12.64. Linear-Move System Pumping Water from Ditch a. Ditch on the Edge of the Field b. Ditch in the Center of the Field Fig. 12.65. Operation Scemes of Ditch-fed Linear-Move Systems Linear-Move systems that pump from ditches must have a self-contained pump and Fig. 12.63. Linear-move – Main-line in Field Margin
- 208. SPRINKLER IRRIGATION 187 motor poweredby an on-board diesel engine or electric motor fed via an auxiliary cable A major drawback of Linear-Move systems, as compared to Center-Pivot systems, is the need of driving the lateral back to the starting position. Since the Center-Pivot lateral operates in a circle, it naturally ends each irrigation cycle at the beginning of the next. The Linear-Move travels from one end of the field to the other, its ending position is the maximum distance away from the starting position; down-time results if the machine is returned “dry” (not applying water). When the lateral reaches the far end of the field, it has to be moved back to the beginning. This means moving a heavy machine over recently irrigated land. On sandy soils this may not be a problem, but on fine-textured soils the towers may sink into the soil even when crawler tracks are used. It may be necessary to wait a few days to reposition the system. Several alternatives exist to overcome this obstacle. a. Dividing the field into two sub-plots in its middle. Irrigation starts on one edge and continues to the center of the field. The lateral then is moved dry to the other end where irrigation starts again toward the center of the field. Upon reaching the center, the lateral can be conveniently moved dry without irrigation to the first edge to start the next irrigation from the initial position. b. Another alternative is to operate the Linear-Move system in both directions, applying half of the water deficit and then moving back applying the second half of the water amount for deficit replenishment. c. In another operation practice, the lateral is half as long as the the width of the irrigated area. On one pass the lateral irrigates half of the field, when reaching the end of the field, the lateral can pivot at one end and on the return pass it irrigates the other half of the field. When the irrigation is complete, the lateral again pivots to return to the starting position. This type of operation combines some features of Linear-Moves and Center-Pivots. The main advantage of a Linear-Move system over Center-Pivot is that it can fully irrigate a rectangular field. Another advantage is the uniform water application-rates along the lateral, resulting in simpler sprinkler package design and lower peak application-rates. 12.5.4. Control and Automation Center-Pivot and Linear-Move systems are operating on varying topography and varying soil textures, under a single machine. Soils of low infiltration rates pose the need to apply little or no irrigation water to some areas while fully irrigating others. These situation commits using some sort of monitor/controller to manage water applications based upon local real-time requirements. Precision application, variable rate irrigation and site specific irrigation are recently developed practices employing water application controlling devices, capable of maximizing the economic and the environmental value of the water applied via a moving irrigation system. Contemporary Center-Pivot and Linear-Move machines are assisted by sophisticated instrumentation and procedures in applying precisely the desired water amount in fields of great variance of soil types, topography, plot shape, crops, growth phases and seasons. These devices include sensors, monitors, on-off switches, pressure and flow regulators, wired and wireless (RF radio, Cellular, internet) communications,
- 209. SPRINKLER IRRIGATION 188 controllers andcontrol panels. These means facilitate remote control and data acquisition. Some systems send audio and visual alarms about system or water supply malfunction, including calling operators via radio or mobile phone. There are control centers that can monitor many Center-Pivots and coordinate operations and maintenance activities. Electronic sensors, controllers, and communication protocols have been developed to meet the growing interest in site-specific irrigation using Center-Pivot and Linear- Move irrigation systems. On-board and field-distributed sensors can collect data necessary for real-time irrigation management decision-making and transmit the information directly or through wireless networks to the main control panel or computerized controller. Control devices necessary to alter water application depth for relatively small management zones are now commercially available. Selection of the communication system for remote access depends on local and regional topography and cost. Communication systems such as cell phones, satellite radios, and internet based systems allow the operator to query the main control panel or base computer from a remote location at any time. Modern mechanized units are equipped with sophisticated controllers that enable full control of the velocity of motion, flow-rate, irrigation start and water shut-off, as well as protecting against pressure surges and bursting of pipes. Sensors enable the precise control of advancement speed, alignment of the entire lateral along its path and water shut-off at arriving the field boundary. In Linear-Move systems, guidance is provided by signals emitted from buried electrical wire, by an above-ground guide cable stretched along one of the field edges, or by a guide wheel that follows a small furrow. Antennas in the control tower sense the buried wire and transmit the signal to a guidance control box. Levers on the control tower are activated by the guidance cable or wheel and align the lateral to follow the line. Many machines are equipped with GPS systems that enable precise movement that had been pre-deigned on the irrigated plot map. With easy-to-use mapping software, VRI (Variable Rate Irrigation) allows growers to create custom irrigation zones that can be distinguished according to soil type, topography, crop type or field obstacles. The variable rate program is loaded into the VRI controller that through wireless nodes, command individual or group of emitters to change application-rates over different crops or soil types. Fig. 12.66. VRI with Individual Emitter Control – Each Emitter (or a Group of Emitters) is Programmed to Turn On/Off or Pulse in Customized Rate
- 210. SPRINKLER IRRIGATION 189 Fig. 12.67.VRI – Partially Irrigating Lateral A variable flow sprinkler was developed for controlling irrigation water application. It employs a mechanically-activated pin to alter the nozzle orifice cross-section area which adjusts the sprinkler flow-rate in the range of 35% - 100% of its rated flow rate, based upon operating pressure. The pin is controlled by either electric or hydraulic actuator. Its drawback is that the wetting pattern and water droplet size distribution change with the change of the flow-rate and decrease water application uniformity due to change in overlapping pattern. Fig. 12.69. Control Panel Positioned in the Pivot point Fig. 12.68. Individually Controlled Node
- 211. SPRINKLER IRRIGATION 190 Changing thewater depth application with a center-pivot can be accomplished by adjustment of the center-pivot travel speed based upon soil properties, topography and crop variance. Programmable control panels allow adjustment of the speed of travel multiple times during an irrigation event. This is accomplished by pre-definition of the field position in a circle of 3600 , where the speed will be changed to apply more, less or no irrigation water, where portions of the field were planted with different crops or remained fallow. Sensors assist in controlling the position of a center-pivot system. Commercially available center-pivots employ a Wide-Area Augmentation System (WAAS) with enabled GPS antenna option to identify the position of the end tower in < 3 m. accuracy. The stop-start cycle of the center-pivot typically allows determination of system position to less than 1 m accuracy. The net effect of being able to accurately determine the pivot lateral location is that management zone size can be reduced without increasing the potential for a misapplication of water, nutrients, or pesticides. Nowadays, Wireless Sensor Networks (WSN) are favored over wired networks, since they minimize problems and reduce costs associated with stretching and maintaining wires across the field. Decision support frameworks rely on WSNs for real-time, automated, low power soil water and micro-meteorological instrumentation. Infrared thermometers monitor plant temperatures and diverse sensors provide continuous feedback of field conditions. Sensors can be mounted on the machines and provide real-time feedback for decision support as the machines move across the field. Local field-based sensor systems combine data acquisition from automated agricultural weather stations and WSNs that directly collect localized field parameters data from diverse sensor types. Field sensors measure soil moisture levels, air temperature and relative humidity, precipitation (from rain and irrigation) and infrared (IR) surface radiometric measurements. Wireless communication transmits the data to a controller situated on the irrigation machine or in a remote location. Spectral and thermal ground-based remote sensors mounted on self-propelled irrigation machines, provide information in real-time. Infrared thermocouple thermometers mounted on a moving pivot lateral can measure the temperature of in- field crop canopy. The use of wireless sensors and wireless sensor networks has some confinements and drawbacks. The needed provision for ample bandwidth, existing inefficiencies in routing protocols, electromagnetic interference, impediment by vegetation, radio transmission range limits and sensor battery life. When the moving system is used as the sensor platform; Signal disturbance issues relating to crop height and in-field equipment are inherently reduced, compared to in- field sensors that require manual adjustment above crop canopy. 12.5.4.1. Remote Communication with Mechanized Irrigation Systems There are several techniques for remotely communicating with self-propelled sprinkler irrigation systems. These include cell phones, RF radios, and satellite radio communications for basic monitoring and control of the systems. Hybrid systems relying on internet connected to computers at the site employ wireless RF for connecting to the machine. Manufacturers have developed hardware and software
- 212. SPRINKLER IRRIGATION 191 that allowthe operator to access the main control panel from anywhere to determine system status - position in field, travel direction, speed of travel and application depth. Visualization software allows the operator to watch details of the irrigating systems in real-time, year-to-date summaries of water and chemical application events. All the data can be archived for record keeping purposes. Fig. 12.70. On-screen Operation Presentation Selection of the communication system for remote access depends on topography and costs compared with other systems. Cell-phone with modem at the control panel is the most common and least costly alternative. Satellite radio communications are preferable when there are large topographic differences that limit cell phone service. Higher powered, licensed, radio systems (e.g., 5-10W) with data modems are another option but may also be affected by topographic interference.
- 213. SPRINKLER IRRIGATION 192 13. PLANNINGAND DESIGN OF SPRINKLER IRRIGATION 13.1. Introduction Planning and design of irrigation systems is a step-by-step procedure. Setting up a new irrigation system has two phases: a. Planning b. Design Planning is the preliminary stage that consists of collecting data, taking decisions about the irrigation regime, choosing the layout and the components of the system, defining the emitter type and flow-rate. The hydraulic design is the next stage that comprises of mapping the irrigation system layout, locating control units, mains and laterals, calculating and determining the pressure-flow regime and programming the operation timetable. This phase can be supported by dedicated computer software provided the programmers have a sound understanding of the fundamentals of hydraulic design. 13.2. Planning Basic pre-design data to be collected: plot boundaries and topography, soil properties, climate data, cropping technology, crop water requirement, water-supply capacity and quality, existing equipment. The topographic map of the plot will be scaled to 1:500 (for small plots) – 1:2500 (for large blocks). It will incorporate topography, plot boundaries, crop spacing, row direction and partition into sub-units. If the irrigated area is an orchard, the grid of the trees along the rows will be sketched. In existing orchard, air photo can be referred, if applicable. Intervals between elevation contours will not exceed 1 m. It is recommended to carry out a soil survey, to define the soil texture and structure, soil permeability, encrustation, etc. It is essential to check whether compact soil layers or a high water table exist. 13.2.1. Soil Properties a. Soil depth b. Soil texture and structure c. Bulk density d. Saturation Percentage, Field Capacity, Permanent Wilting Point e. Infiltration rate and hydraulic conductivity data, if available f. Presence of stratified layers and cracks g. Soil salinity Fig. 13.1. Topographic Map
- 214. SPRINKLER IRRIGATION 193 Fig. 13.2.Irrigation Planning Form
- 215. SPRINKLER IRRIGATION 194 13.2.2. ClimateData a. Rainfall – amount and seasonal distribution. b. Reference Evapo-transpiration (ET0) – calculated from climatic variables (Penman-Monteith method) or measured in Class A pan. 12.2.3. Cropping Data a. Growth season b. Phenological stages – dates, time-length, foliage coverage, root-zone depth, sensitivity to water stress. c. In-row and between row spacing. d. Peak season crop coefficient (kc): the ratio between ETc (crop water loss by evapo-transpiration) and the ET0. The crop coefficient kc has been elaborated for use in fully wetted soil surface technologies like overlapping sprinkler irrigation. For partial soil surface wetting technologies, the ETc may be adjusted downwards. The component of evaporation from soil surface is significantly reduced in partial wetting pattern, due to the small percentage of wetted soil surface. The adjustment can be made using the equation: ETca = ETc × [0.1(GC)0.5 ] (Eq. 13.1) Where: ETca = Adjusted ETc GC = Percentage of ground cover, The percentage of ground cover relates to the shaded soil surface by the crop foliage at midday. 13.2.4. Water resources The second set of data is the water source and the water quality. 13.2.4.1. Water Supply Capacity The parametrs needed for system design: a. Water source characteristics (river, dam, pond, well, public/commercial supply). b. Hours of supply (if by external supplier or due to restrictions on electricity supply) c. Maximum available hourly/daily flow-rate (discharge). d. Pump pressure-discharge curve (if applicable). e. Pressure at supply connection (if by external supplier). f. Water quality (physical contamination, hardness, salinity). If a public or commercial supplier provides the water, the head, maximum available flow-rate at the supply points and supply hours have to be validated. Additional data have to be gathered about the crop water requirements, the climate conditions, the amount and the season of rainfall and the sensitivity of the crop to the irrigation-dependent environment factors like salinity and the wetting of the foliage. With the above-mentioned data at hand, the selection of the irrigation method and emitter can be considered. The parameters to be considered are the application-rate that has to correspond to the water intake-rate of the soil, the duration of the application that has to correspond with the wind conditions, water quality and crop sensitivity to foliage
- 216. SPRINKLER IRRIGATION 195 wetting. Crucialfactors are the cost of the equipment, investment capital at hand and the operational costs. After the optional alternatives have been scrutinized, the selection of the emitter type and nozzle size can take place, using manufacturers' catalogs. The tables in the catalogs present the flow-rate (discharge) in the allowed working pressure levels. They also specify the wetting diameter, the allowed spacing between the emitters and the application-rate in those spacings. At this stage, the actual design of the irrigation system can take place. In order to achieve a satisfactory discharge uniformity between all the emitters operating simultaneously in the irrigated sector, the maximum difference in flow-rate between emitters has to be lower than 10%. This allows the maximum head difference in the simultaneuousely irrigating emitters to be 20%. To calculate accurately the water-flow and pressure regime in the irrigated plot, the outline of the irrigation network has to be projected on the topographical - rows grid map. 13.3. Data Manipulation The capacity of the irrigation system has to correspond with the most demanding crop water requirements, namely peak water consumption by the crop. That takes place when foliage coverage is maximal, and/or evaporation is in its peak and/or crop sensitivity to water stress is the highest. In the case of annual crop rotation, data relating to the most demanding crop will be taken into account. The optimal irrigation regime of a given plot has to be based on the water consumption by the crop, soil water retention and the irrigation system layout. 13.3.1. Soil Wetting Pattern In sprinkler irrigation there are two patterns of wetting the soil: a. Full soil surface coverage by overlapping emitters. That pattern prevails with overhead sprinkler irrigation of field crops, vegetables and flowers in the open field and in greenhouses, as well as in overhead irrigation by irrigation machines. b. Partial soil surface coverage by emitters that do not overlap the wetted area by each other. That pattern prevails in under-canopy sprinkler irrigation in orchards, low pressure irrigation with irrigation machines and with micro- irrigation. The partial soil wetting pattern by non-overlapping sprinklers requires assessment of the percentage of soil volume that is wetted. Diverse models for estimating the wetted volume were developed in which the wetting pattern is determined by: a. Emitter flow-rate b. Infiltration rate of the soil (expressed in mm/h) c. Soil hydraulic conductivity (expressed as mm/s). The difficulty with the last two parameters is that the infiltration rate is not cosistant and decreases in irrigated soil along time. The hydraulic conductivity is measured in the laboratory on disturbed saturated soil. Frequently, the results of the modeling do not coincide with the actual wetting pattern in undisturbed soil in the field.
- 217. SPRINKLER IRRIGATION 196 A customarycompromise made in localized irrigation is the estimation of the percentage of wetted area. This facilitates use of methodology that had been developed for determining the irrigation regime in full surface wetting technologies, corrected with multiplication by the cover percentage factor. 13.3.1.1. Units of Water Consumption Water depletion and replenishment amounts are expressed in two alternative values: a. mm/day (mm/hour in greenhouses) – designates virtual coverage of the whole surface area in the plot by a uniform water layer of a designated depth in mm. b. m3 /ha./day (or inch/acre/day) Conversion formula: (mm/day) × 10 = m3 /ha./day. 13.3.2. Manipulation Steps 13.3.2.1. Calculation of the Permitted Depletion of Water from the Soil: MAD = (FC – PWP) × BD × Waf × Sd × D × Sl (Eq. 13.2) Where: MAD = Management Allowed Depletion - the permitted water deficit – mm = l/m2 (×10 = m3 /ha) FC = Field Capacity % w/w (weight of water per weight of soil) PWP = Permanent Wilting Point % w/w FC – WP = Available water % w/w BD = Bulk Density g/ml Waf = Permitted depletion fraction of the available water Sd = Desired wetting depth D = Maximum horizontal wetting diameter Sl = Spacing between laterals Example: FC = 20% w/w PWP = 15% w/w Available Water (AW) = 20% - 15% = 5% w/w# BD = 1.4 Available Water = 5% × 1.4 = 7% v/v## Waf = 0.4 Allowed deficit = 7% × 0.4 = 2.8% v/v Sl = 1.60 m D = 0.60 m Percentage wetted area = 0.60/1.60 = 37.5%* Sd = 0.90 m Wetted volume per ha = 10,000 m2 × 0.90 m × 37.5% = 3375 m3 Allowed deficit per ha. 3375 × 2.8% = 94.5 m3 = 94.5/10 = 9.45 mm # w/w = Weight of water per weight of soil ## v/v = Volume of water per volume of soil. 13.3.2.2. Assessing the Wetted Volume Assuming full overlapping of the wetted volume by adjacent emitters and ignoring the non-wetted volume. The wetted soil volume has no regular gometric shape. The definition of the wetted volume by a single emitter is not a simple assignment. It is needed for selecting the emitter type, its flow-rate and operating pressure, spacing between laterals and between emitters, as well as for determining water dosage in
- 218. SPRINKLER IRRIGATION 197 irrigation. Due tothe difficulties in precise calculation of the wetted volume, data related to wetting volume are only assessments. System designers rely on their experience or rules of thumb regarding wetting diameters that allow a relatively wide range of wetting diameters for each soil class. Diversity is attributed to variability in soil texture and structure in each class. Great variability may be found in the same irrigating block. The best way of estimating wetting volume is on-the-spot field examination of the chosen emitter in undisturbed soil in the specific plot. 13.3.2.3. Determining the Irrigation Regime When considering the irrigation regime, the allowed deficit should be compared to the crop water requirement. The first step is to calculate the gross daily water replenishment requirement relating to the irrigation efficiency (IE) of the irrigation system: ETca --------------------Wgr = IE (Eq. 13.3) Where: Wgr = Gross water requirement - mm/day ETca = Adjusted crop water requirement – mm/day IE = Irrigation Efficiency - % Irrigation Efficiency is defined as: Water beneficially used -------------------------------------------------------------------------------------IE = Irrigation water applied × 100 (Eq. 13.4) Irrigation Efficiency is an arbitrary average value assigned to the irrigation technology. The common values are: a. Border flood irrigation: 50% - 80% b. Furrow irrigation: 70% - 80% c. Sprinkler irrigation: 85% - 90% d. Microsprinklers and microjets: 80% - 90% e. Drip irrigation: 80% - 95% Example: ETca = 6 mm/d IE = 90% Wgr = 6/90% ≈ 6.7 mm/d 13.3.2.4. Time Intervals between Irrigations Calculation of the time interval between applications has to relate to peak demand and stress-sensitive phenological phases. The data required for determining the interval: a. Soil water retention – available water. b. Acceptable depletion fraction of the available water. c. Root-system depth.
- 219. SPRINKLER IRRIGATION 198 d. Dimensionsof the wetted volume or the percentage of wetted area out of the total spacing area. The intervals between applications will be calculated by division of the water amount needed for replenishment of the depleted water by the daily gross water requirement. Wad ------------------------TI = Wgr (Eq. 13.5) Where: TI = Time interval between irrigations – days Wad = The allowed water depletion – mm = l/m2 (×10 = m3 /ha) Wgr = Gross water requirement - mm/day Example: Wad = 9.45 mm Wgr = 6/90% ≈ 6.7 mm/d TI = 9.45/6.7=1.41 days In this case, the interval will be the integer value (1) and the water dose will be adjusted respectively. In frequent greenhouse irrigation, intervals are measured in hours. Here, the interval will be 24h ×1.4 ≈ 33 hours. 13.4. Existing Equipment Existence of pumping equipment, delivery and distribution pipelines, accessories, etc. that can be incorporated into the designed system.
- 220. SPRINKLER IRRIGATION 199 Table 13.1.Sprinkler Performance Data Provided by Manufacturer (example)
- 221. SPRINKLER IRRIGATION 200 13.5. CalculationFormulae There are some helpful formulae and tables that support decision-making in the designing process: Emitter lateral discharge (flow-rate) (Eq. 13.6) Q = lateral discharge m3 /h q a = discharge of an emitter at the mean head of the lateral - m3 /h n = number of emitters on the lateral q 0 = discharge of the distal emitter P n = pressure at the entrance to the lateral (bar) P 0= pressure at the distal emitter bar. Average pressure in the emitter lateral (Eq. 13.7) P a = average pressure in the lateral (bar) P 0 = pressure at the distal edge of the lateral (bar) P n = pressure at the initial edge of the lateral (bar) Maximum allowed pressure difference (bar) among emitters operating simultaneously (Eq. 13.8) Pf20 = allowed pressure difference, 20% of highest head in an emitter in the plot (bar). P0 = pressure at the distal edge of the lateral (bar). Pn = maximum emitter pressure in plot (bar). The head-losses by friction in the pipes are calculated and the effect of topography is added-on, using the specific slide-rulers, nomograms or computer software. Two important rules have to be followed along the planning design process: The lowest head in the plot has to be in the range of the allowed working head of the emitter. The class of the pipes in the plot has to correspond with the forecasted maximum working head. 13.6. The Design Procedure 13.6.1. Overview Once all the preliminary steps have been completed, the topographical map has been prepared and the general layout decided upon, the network is drawn. The average flow-rate in the design pressure in the emitters is calculated for representative laterals and then at the sub-mains and the mains. Expression of the water head in units of meter head (0.1 bar) simplifies the procedure of the calculation of head-losses. The friction head-losses by water-flow in
- 222. SPRINKLER IRRIGATION 201 the pipesand the accessories are expressed in the same unit system that indicates the topography effect on water head. Elevation rise of each meter in the topographic height decreases the water head by 1 m. The accessories: valves, filters, etc. are chosen according to the required capacity. The local head-losses are determined and registered on the map. After the design is completed, the system head-losses are checked again, step-by-step, from the control head to the last emitter. The outcome of the design process is: a. Network map with all the data registered. b. List of equipment. c. Detailed budget. d. Operation scheme Table 13.2. Maximum Allowed Number of Sprinklers on Lateral on Level Ground PIPE TYPE ALUMINUM HDPE (RIGID POLYETHYLENE) Diameter 2” 3” 50 mm 63 mm 75 mm Sprinkler Distance 6 12 6 12 6 12 6 12 6 12 flow-rate m 3 /h between sprinklers m 0.8 Maximum 18 13 35 27 18 13 25 20 35 26 1.0 allowed 15 12 30 24 18 12 22 17 30 23 1.2 number of sprinklers on 13 10 29 22 13 10 19 15 27 21 1.4 the lateral 12 10 27 21 12 10 17 14 25 20 1.6 11 9 24 20 11 9 15 13 23 19 1.8 10 8 22 18 10 8 14 12 20 17 13.6.2. System layout The actual design is separated into two phases: 1. Layout of laterals and manifolds. 2. Layout of the mainline and the submains. When designing irrigation systems, it is imperative to analyze several alternatives, comparing initial investment cost, labor and energy expenses. Choosing the optimal layout depends on diverse and frequently contradicting considerations. Longer laterals may enable shorter mains and submains and saving of accessories but commit the use of larger pipe diameters. Comb layout saves outlets but necessitates larger diameter of the distributing line.
- 223. SPRINKLER IRRIGATION 202 Frequently, itis economically favorable to lay manifolds of smaller diameters that reduce the cost of fittings in expense of the additional cost of the manifold piping. Manifolds simplify operation and automation in case of the need to split the plot for separate water applications. The primary phase in the design of the system is the calculation of the head- losses created by the water flow. There are diverse procedures for calculating head-losses. In the past, designers used tables, slide rulers and nomograms. Dedicated software for irrigation design and on-line calculators replaced 1. Comb layout 2. Splitted comb 3. Central fishbone 4. Asymmetric fishbone 5. Splitted fishbone 6. Dual fishbone Fig. 13.3. Different Design Alternatives Fig. 13.4. Manifolds Save in Cost of Accessories
- 224. SPRINKLER IRRIGATION 203 those oldfashion procedures. Emitter manufacturers indicate the maximum allowed length of laterals on flat land and in sloping ground, keeping emitters' flow-rate variance in laterals within 10% (+/- 5% of the average). The design practice is divided into two phases. In the first phase, pressure (head) losses are calculated from the distal end to the head of the plot, using nominal values of pressure and flow-rate. In the second phase, the design is checked and adjusted, going from the plot head to the distal end. At this stage, the calculation relates to actual data of flow-rate and head-losses. The map of the plot is divided into sectors and detailed calculations are performed on each pipe segment. The data have to be registered in a design form. Head-losses in accessories can be calculated using the concept of equivalent length (see nomogram in page 105). The data manipulated with this concept present head-losses in a virtual pipe of the same diameter as that of the accessory. Most manufacturers provide tables and nomograms of the head-losses in their equipment. Local head-loss in an accessory can be also calculated, using its flow factor (Kv), if available. 13.6.3. Water Flow Velocity Water flow velocity determines the head-losses in the system. As flow velocity increases, the head-losses are amplified. In flow velocity over 2.5 m/second, the energy waste due to head-losses decreases the economic viability of the system. In mainlines, high velocities may trigger water hammer that results in pipe burst. Hence in the preliminary phases of design the expected velocity in manifolds is kept within the range of 2 – 2.5 m/second and in mainlines below 1.5 m/second. 13.6.4. Spacing Spacing between laterals and between emitters on the lateral is determined by the spacing between rows and plants in the row, Soil depth, its texture and the characteristics of the root system. 13.6.5. Choosing Emitters and Laterals Choosing of the emitter and lateral type will relate to the farming technology. The chosen emitters and their flow-rate will correspond with spacing, planned irrigation regime, soil permeability and the capacity of the water supply system. Additional considerations are crop response to water distribution patterns and climate control requirements. 13.7. Example of the Design Process 13.7.1. Design of Micro-irrigation System in Orchard Micro-jets and micro-sprinklers have flow-rates in the range of 20 – 200 l/h. The common layout in orchards is of one lateral per row. In densely planted rows of 2 - 3 m. distance between trees in the row, one emitter can suffice per two trees. Over 3 m. distance in the row, one emitter per tree is the prevalent layout. In some more spacious plantations with spacing greater than 6 ×××× 6 m, two emitters per tree are frequently installed. The placement of the emitter in the row depends on the shape of the tree canopy. In those crops that the canopy leaves considerable height above soil surface free for water distribution, the emitter is placed in the middle between two
- 225. SPRINKLER IRRIGATION 204 trees. Intrees that their canopies bend toward the soil surface, converge with each other in the middle between the two trees, the emitter is placed 0.5 – 1 m. from the trunk. There are pressure compensating and non-pressure compensating emitters. The choice between micro-sprinklers, micro-jets and ray-jets takes place in respect to spacing, soil type and crop response. In large spacing, micro-sprinklers that wet greater area are favored, in densely planted orchards, micro-jets are more suitable and in heavy and compact soils, prone to run-off, as well as in windy conditions, ray- jets are the best performers. Crop Data Crop: Citrus Variety: Washington Navel Area: 11.5 Ha. Partition: 4 blocks, 80 X 360 m, each Topography: 3.5 m slope from NW to SE Spacing: 6 X 4 m. Irrigation season: April - October Harvest: October-December Active root system depth: 100 cm Maximum allowed water depletion: 60% Peak-season average reference evaporation (ET0): 8 mm/day Peak-season crop coefficient: 0.7 Soil data Texture: Loamy clay Depth: 1.20 – 1.50 m Bulk Density: 1.4 Field Capacity: 32% V/V Permanent Wilting Point: 15% V/V Available Water: 17% V/V Wetted area percentage: 60% Climate Data Peak season average daily class A pan evaporation: 8 mm Water Supply Data Maximum supply hours: 20 hours a day Maximum available hourly discharge: 150 m3 /h Fig. 13.5. Citrus Grove - 11.5 Ha
- 226. SPRINKLER IRRIGATION 205 EC water:1.2 dS/m Chloride content: 150 mg/l Calculation of daily Peak Season Water Demand Daily average evaporation ×××× Crop coefficient = 8 mm ×××× 0.7 = 5.6 mm/day Gross daily demand, assuming application efficiency of 80%: 5.6/80% = 7 mm/d Soil water reservoir volume per ha: Inter-row spacing ×××× root system depth × wetted area percentage = 10,000 m × 60% × 1.00 m = 6000 m3 Easily available water soil capacity = resrvoir volume × available water (%)× Allowed deplition (%) = 6000 m3 × 17% × 60% = 612 m3 /ha. = 61.2 mm Max interval between irrigations = easily available water soil capacity / daily demand = 61.2 mm / 7 mm/day = 8.75 days For sake of convenience, the interval will be 7 days and not the allowable maximum. Irrigation dose: 7 mm/day × 7 days = 49 mm. Minimum acceptable application rate: 49 mm/20hours of water supply = 2.45 mm/hour. Minimum emitter flow-rate in 4××××6 m spacing: 2.45 mm/(4×6)m = 102 l/h Choosing emitter The chosen emitter is non-regulated (non-compensating) jet+ with nominal flow-rate of 102 l/h in 20 m head. The chosen lateral is the 20/4 mm (20/17 mm OD/ID). It allows for 11 emitters on the lateral, in the range of pressure difference of 7.5% in 1% ascending slope. Table 13.3. The Chosen Emitter Performance
- 227. SPRINKLER IRRIGATION 206 Table 13.4.Allowed Length of Laterals Table 13.5. Basic Data Parameter Unit Amount Nominal flow-rate Micro-jet piece 1 102 l/hour Lateral m 40 Emitters distance on lateral m 4 Emitters per lateral piece 40/4 = 10 102 l/h ×××× 10 = 1.020 l/h Number of laterals per block piece 60 61.2 m3 No. of blocks in the plot unit 8 489.6 m3/h Irrigation cycle day 7 Days of irrigation in a cycle day 4 Flow-rate per a single day .m3/h 489.6 / 4 = 122.4 m3/h
- 228. SPRINKLER IRRIGATION 207 Fig. 13.6.The Design Scheme
- 229. SPRINKLER IRRIGATION 208 Table 13.6.Head-loss Calculation Segment Flow- rate m3/h Length - m N.D./PN mm/class H f - % Outlets F- factor Hf - m Hz - m Total ∆H- m Cumulative ∆H - m EF 1.02 40 20/4 13 10 0.35 1.8 0.5 2.3 2.3 DE 24 72 75/4 4 12 0.35 1.0 1.0 2.0 4.3 DG 36 108 75/4 8 18 0.35 3.0 -1.0 2.0 BD 60 148 PVC 110/6 3.0 0 1.0 4.4 1.0 4.4 8.7 KL 1.02 40 20/4 13 10 0.35 1.8 0.5 2.3 2.3 IK 24 72 75/4 4 12 0.35 1.0 0 1.0 3.3 MN 1.02 40 20/4 13 10 0.35 1.8 0.5 2.3 IM 36 108 75/4 8 18 0.35 3.0 -0.5 2.5 BI 60 388 PVC 110/6 3.0 0 1.0 11.6 -2.0 9.6 15.2 RS 1.02 40 20/4 13 10 0.35 1.8 0.5 2.3 2.3 OR 24 72 75/4 4 12 0.35 1.0 1.0 2.0 4.3 PQ 1.02 40 20/4 13 10 0.35 1.8 0.5 2.3 OP 36 108 75/4 8 18 0.35 3.0 -1.0 2.0 BO 60 228 PVC 110/6 3.0 0 1.0 6.8 0.5 7.3 11.6 UV 1.02 40 20/4 13 10 0.35 1.8 0.5 2.3 2.3 TU 24 72 75/4 4 12 0.35 1.0 1.0 2.0 4.3 WY 1.02 40 20/4 13 10 0.35 1.8 0.5 2.3 TW 36 108 75/4 8 18 0.35 3.0 -1.0 2.0 BT 60 308 PVC 110/6 3.0 0 1.0 9.2 -05 8.7 13.0 Table 13.7. Total Requested Dynamic Head Pressure requested in lateral distal end 20 m Head-loss in lateral 1.8 m Topographic difference 2 m Maximum friction head-losses 14.1 m Control head-losses 8 m Total 45.9 m Comments a. An emitter of great wetting diameter had been chosen since the citrus trees have an active shallow root-system that expands significantly beyond the canopy boundaries.
- 230. SPRINKLER IRRIGATION 209 b. Therequested dynamic head relates to the most critical water delivery point. c. The head-losses could be decreased by 6 m. head by choosing sub-mains of larger diameter – 140/6 mm. But since the water velocity in 110/6 mm pipes is lower than 2 m/sec it is doubtful if the increased pipe diameter is economically worthwhile. That depends on the cost of energy and has to be considered in respect to local circumstances. d. For sake of minimum head-losses, two blocks will be irrigated per day: Day 1: blocks a + e Day 2: blocks b + f Day 3: blocks c + g Day 4: blocks d + h 13.7. Additional Examples of System Design Schemes PLANNING DATA Area … 384 m X 864 m = 331,776 m2 ≈≈≈≈ 33 Ha. Cycle ……………………..80 mm every 12 days Working Pressure ………………. 30 m (3.0 bar) Sprinkler Flow-rate …………………….. 1750 l/h Sprinkler Spacing ……………….…12 m X 18 m Application-rate …………………………. 8 mm/h Application time length ….. …………….…..10 h No. of Daily Shifts ……………………. 2 per set No. of Simultanuously Operating Sprinklers 64 Total System Discharge ……………… 112 m3/h Main Line Diameter ……………… 140 / 110 mm Lateral Diameter …………………………….…. 3" Fig. 13.7. Hand-move Design Scheme
- 231. SPRINKLER IRRIGATION 210 PLANNING DATA System…..….Manual Shift on 75 mm Laterals Area … 768 m X 960 m = 737, 280 m2 ≈≈≈≈ 74 Ha. Cycle …………………….. 85 mm Every 16 Days Working Pressure ……………….. 45 m (4.5 bar) Sprinkler Flow-rate ……………………. 25 m3/h Sprinkler Spacing ……………….. 48 m X 60 m Application Rate …………………….. 8.6 mm/h Application Time-length ……………………. 10 h No. of Daily Shifts ……………………………..… 2 No. of Operating Sprinklers ……………………. 8 System Discharge ……………………… 200 m3/h Main-line Diameter…………. 140 / 125 / 110 mm Lateral Diameter…………………………… 75 mm Fig. 13.8. Gun Traveler Design Scheme
- 232. SPRINKLER IRRIGATION 211 PLANNING DATA System……..…………...Solid-set under-canopy Area …..… 160 m X 100 m = 16'000 m2 = 1.6 Ha. Cycle …………………..…... 35 mm every 7 days Working Pressure ……………….. 25 m (2.5 bar) Sprinkler Flow-rate ………………………… 70 l/h Sprinkler Spacing …………………….. 4 m X 6 m Application Rate …………………………. 3 mm/h Application Time-length ……………………. 12 h No. of Daily Shifts ……………………………..… 1 No. of Operating Sprinklers ……………..…. 300 System Discharge ……………….……… 21 m3/h Main-line Diameter……………..……. 75 / 63 mm Sub-mains Diameter……………………… 50 mm Laterals Diameter ………………………… 20 mm Fig. 13.9. Solid-set in Orchard Design Scheme
- 233. 212 SPRINKLER IRRIGATION 14. IRRIGATIONSCHEDULING 14.1. Introduction A key-factor in successful sprinkler irrigation is the optimal scheduling of irrigation, corresponding with crop water requirements, soil properties, water supply constraints and the irrigation system characteristics. Optimal scheduling guarantees efficient water use, provided the performance coincides with the program. The process resembles somewhat the initial step of irrigation planning, but relates to real time conditions while in planning the calculation is done for peak system requirements. Table 14.1. Annual Crops Irrigation Scheduling Form Crop : ……………………………….. Soil type: …………………………… Growing period : ………………….. Irrigation Method: ………………… A. Growth stage Establi’ Vegetat’ Floweri’ Fruit fo’ Ripenin’ Total B. Stage length – days C. Period – dates D. Wetting Area - Percentage E. Anticipated rainfall – mm/stage F. Rainfall efficiency - % G. Effective rainfall – mm/stage H. Average daily evapotranspriation– mm I. Total evapotranspiration per stage-mm J. Precipitation balance per stage – mm K. Field capacity - % per weight L. Wilting point - % per weight M. Available water - % per weight N. Bulk Density – g/cm3 O. Available water - % per volume P. Average root zone depth/stage – cm Q. Available water in root zone – mm R. Available water depletion - % S. Allowed water deficit – mm T. Crop coefficient per stage U. Average daily water uptake – mm V. Interval between irrigations – days W. Net water amount per irrig’ – m3/Ha X. Irrigation efficiency - % Y. Gross water application – m3/Ha
- 234. 213 SPRINKLER IRRIGATION The relateddata concerning crop water requirements, climate and soil parameters is entered into the form and the dosage per each application is calculated step-by-step manually or by a computer worksheet. 14.2. Calculation of the Water Amount in Sprinkler Irrigation The application rate of the irrigation system depends on the below written variables: a. Type of sprinkler and nozzles b. Spacing - the distance between the laterals x the distance between the sprinklers along the laterals. c. The pressure head at the sprinkler nozzle (the higher the pressure, the greater the amount of water flow-rate of the sprinkler). According to this data it is possible to calculate the desired precipitation rate: Precipitation rate: amount of the water (m3 ) applied to 1000 m2 (O.1 hectare) in 1 hour. Each m3 /h per 1000 m2 = 1 mm. 14.2.1. Calculation of the Precipitation Rate Example: Sprinkler type: 233/92 Nozzle sizes: 3.4 mm x 2.5 mm. Pressure head at sprinkler nozzle: 2.5 bar Sprinkler flow-rate at that pressure head (taken from performance table): 1.06 m3 /h. Spacing of sprinklers: 9 m x 12 m. The area irrigated by one sprinkler: 9 X 12 = 108 m. Precipitation rate = Sprinkler flow-rate l/h / irrigated area m. = 1060/108 = 9.8 mm./h. Precipitation of I mm/h means 10 m3 per hectare/h. 9.8 mm/h. = 98 m3 /hectare/h. 14.2.2.Calculation of the Irrigation Duration (Eq. 14.1) T = Irrigation time length (hours) W = Gross water requirement mm. Pr = Precipitation rate mm/h. Example: The required irrigation water amount: 600 m3 /ha. = 60 mm. The precipitation rate: 9.8 mm/h. Irrigation time-length: 60/9.8 = 6.1 hours. 14.2.3.The Total Flow-rate of the Irrigated Area The gross water volume per hour (discharge) can be calculated by the multiplication of the average single-sprinkler flow-rate by the number of the simultaneously operated sprinklers. Example: Average single-sprinkler flow-rate: 1.5 m3 /h. The number of the simultaneously operated sprinklers: 345. The gross Flow-rate per application: 1.5 X 345 = 517.5 m3 /h.
- 235. 214 SPRINKLER IRRIGATION In theplanning of the water distribution between different plots, care should be taken to avoid an excessive water flow in the supply and distributing pipeline that would reduce the water head in the irrigated area below the requested working head. 14.2.4. Scheduling with the Water Budget Concept A common methodology of scheduling is the water budget approach. The method is based on climatic data. When used adequately, calculated water amounts are accurate. The procedure is simple and flexible for using in most of the grown crops. The procedure can be divided into several basic steps, which are slightly different for high-volume sprinkler-irrigated orchards than for those where low-volume micro- sprinklers are used. 14.2.4.1. High-volume Sprinkler Systems Step 1. Estimation of the Available Water Amount in the Root Zone For that step, two essential data elements have to be known: The water retention capacity of the soil and the crop root-system depth and pattern. The total available water is determined by multiplying the appropriate available water value by the average rooting depth. Table 14.2. The Estimated Available Water per Unit of Rooting Depth for Soils of Various Textures and the Intake Rate for Various Soil Textures Available Water Capacity (mm of Water/cm of Soil Depth) Intake Rate (mm/hr) Soil Texture Range Average Range Average Sand 0.5 - 0.8 0.65 12 - 20 16.0 Loamy Sand 0.7 - 1.0 0.85 7 - 12 9.5 Sandy loam 0.9 - 1.2 1.05 7 - 12 9.5 Loam 1.3 - 1.7 1.50 7 - 12 9.5 Silt loam 1.4 - 1.7 1.55 4 - 7 5.5 Silty clay loam 1.5 - 2.0 1.75 4 - 7 5.5 Clay loam 1.5 - 1.8 1.65 4 - 7 5.5 Clay 1.5 - 1.7 1.60 2 - 5 3.5 After: Ontario FactSheet 210/560
- 236. 215 SPRINKLER IRRIGATION Fig. 14.1.Typical Root Systems of Field Crops Table 14.3. Active Root-zone Depth of Fruit Trees CROP DEPTH to IRRIGATE cm Apples 90 Cherries 60 Grapes 90 Peaches 60 Pears 60 Raspberries 60 Step 2. Estimation of the Allowable Soil Water Depletion in the Root-zone Allowable soil water depletion is the fraction of the available water in the root zone that can be extracted without causing adverse effects on plant growth, yield and quality. To estimate allowable soil water depletion, the available water amount is multiplied by the allowable depletion factor (30% - 60%, depending on crop and growing phase). Step 3. Estimation of the Water Use Rate of the Crop The average daily water use rates are derived from long-term average weekly maximum evapo-transpiration measurements, multiplied by crop factors. Step 4. Timing of Irrigations The starting point for calculating the timing of first spring irrigation is ideally after a thorough wetting of soil by irrigation or heavy rainfall which brings the soil reservoir to field capacity. If this does not occur, the initial amount of available water in the crop root-zone must be determined by direct measurement with the gravimetric - oven-dry method or indirectly with tensiometers, Watermark. TDR or gypsum blocks. Irrigation timing is determined by subtracting daily water use of the crop from total available water in the root-zone until the soil water amount has been decreased to the allowable depletion level. Step 5. Calculation of the Water Application Amount (Eq. 14.2) In addition to the irrigation system features, irrigation efficiency varies with size and uniformity of the fields and climatic conditions. Water may be lost through deep percolation, runoff and evaporation. Well designed and managed sprinkler systems have 75% - 85% efficiency. Low-volume micro-sprinkler systems usually have higher irrigation efficiency than high-volume sprinkler systems. Step 6. Calculation of Water Application Time-length (Eq. 14.3)
- 237. 216 SPRINKLER IRRIGATION The durationof water application depends on the amount of water to be applied and water intake rate of the soil. If the soil absorbs water slowly, the application rate has to be low enough to prevent the soil puddling and runoff. The meaning is that in fine texture soils the application time-length has to be longer than in soils of coarse texture. 14.2.5. Scheduling Software and On-line Calculators In our days the task of irrigation scheduling, as well as design of irrigation systems is simplified and eased by using dedicated software for design and scheduling irrigation, obtaininig climate data from the internet and using on-line calculators. Fig. 14.2. Irrigation Design Software Screen-shot
- 238. 217 SPRINKLER IRRIGATION Fig. 14.3.Visual Presention of Designed System Fig. 14.4. Scheduling Software Screen-shot
- 239. 218 SPRINKLER IRRIGATION Fig. 14.5.On-line Calculator
- 240. 219 15. MONITORING ANDCONTROL Water and fertilizer can be managed at different levels of monitoring and control. At the basic level, management is based on personal experience, guess-work and intuition without performing actual measurements. In more advanced management levels, soil moisture and nutrient content are monitored, and water and fertilizers are replenished to pre-defined values. 15.1. Monitoring 15.1.1. Soil Moisture Monitoring 15.1.1.1. Tensiometers The tensiometer is the simplest, most widespread mean for monitoring the performance of irrigation systems. Usually, two units are installed at each monitoring point. The ceramic tip of one tensiometer that is installed within the upper layer, at a depth of 15 – 30 cm in the active aerated root-zone, is used for irrigation timing. The second tensiometer is inserted into the lower limit of the active root zone or the desired wetting depth. Twelve – 24 hours after water application it indicates whether the applied water did indeed replenished the depleted water deep enough, in the relevant soil volume. A drawback of the tensiometer is its limited range of tension measurement. It does not measure beyond 80 centibars which in certain crops and soil types, is lower than the irrigation threshold. In tension above 80 centibars it may dry-out and require reactivation. 15.1.1.2. Granular Sensors To overcome this discrepancy, new sensors have been developed. Instead of a ceramic tip that is equalized with soil water, a granulated matrix mixed with gypsum encased in stainless steel housing is employed. The measured parameter is the electrical resistance between two electrodes inserted within the matrix. As the soil moisture increases, the resistance decreases. A conversion table translates resistance readings to water potential values. This sensor measures water tension up to 200 centibars. Fig. 15.1. Tensiometers Fig. 15.2. Watermark Granular Sensor Fig. 15.3 Time Domain Transmissometry Sensor
- 241. 220 15.1.1.3. TDR andTDT Sensors Other soil water measurement techniques are: Time Domain Reflectometry (TDR) and Time Domain Transmissometry (TDT). Both technologies determine the dielectric permittivity of the soil by measuring the time required for an electromagnetic pulse to propagate along a transmission line within the soil. Since the dielectric constant of water is much higher than that of the soil, higher moisture will increase the permittivity and shorten the time gap between pulse emission and its hit in the target receiver. In TDT, one mode (direction) of the pulse is measured while in TDR the pulse is measured after its reflection back to the source. The readings are converted into percentage of water content in the soil, according to prior calibration. More soil moisture measurement techniques such as gypsum blocks, soil capacitance and neutron probing are mostly used in research and only rarely by farmers. 15.1.2. Plant Water State Monitoring 15.1.2.1. Leaf Water Potential Midday leaf water potential indicates the water state of the plant. Measurements are taken at midday. Leaves are cut with their petioles intact. The leaf is then inserted into a pressure chamber (designated pressure bomb). Pressured air is released from a pressurized container into the chamber. A pressure gauge reading is taken when the first drop of sap appears on the cut petiole tip. The measured value indicates the water potential of the plant. In cotton, midday leaf water potential higher than 20 bars indicates water stress. In orchards, the threshold is 14 – 18 bars. This measurement technique is suitable for field crops and certain fruit crops 15.1.2.2. Stem Water Potential In some perennial crops the parameter of leaf midday water potential is not a satisfactory indication of water state. In these crops, stem midday water potential is indirectly measured. The leaves for the test are wrapped for two hours with aluminum foil to equalize the leaf and the stem water potentials. The leaves are cut and checked in the abovementioned procedure. In almonds, stem water potential of 18 – 20 bars is allowed towards harvest but in the stress sensitive phase of fruit set; stem water potential is kept as low as 10 – 12 bars. a. The Selected Leaf b. The Cut Leaf c. The Measurement Implementation Fig. 15.4. The Pressure Bomb From "ICT International" brochure
- 242. 221 15.1.2.3. Trunk Contraction Incertain fruit trees such as avocado, mango and nectarines, daily fluctuations of trunk diameter indicate the water potential of the tree. Measurements are performed by means of dendrometers, using a micrometer to measure the delicate diurnal changes between two metallic plates fixed into the trunk on opposite sides. 15.1.3. Plant Organs Elongation and Expansion In field crops, the rate of inter-node elongation indicates the level of water stress in the plant. In certain fruit trees the rate of fruit expansion is a good indicator of the water state of the tree. 15.2. Irrigation Control 15.2.1. Manual Control Manual opening and closing of valves is the lowest level of control and is rarely used in modern irrigation systems. 15.2.2. Quantitative Automatic Water Shutdown Valves are opened manually but shutdown is automatic after the preset water amount (in automatic valves) has been delivered. 15.2.3. Fully Controlled Irrigation Irrigation is regulated by local and central controllers. The controllers are preset to open the valves in the desired time and to close the system when the preset water amount has been delivered. Central controllers can manipulate weather data – rainfall, temperature and evaporation for irrigation scheduling. Weather stations directly deliver data parameters like relative humidity, radiation and wind velocity, by line or by cellular communication and the internet, for fine-tuning of the water application. 15.2.4. Integrated Irrigation and Fertigation Control Integrated control of irrigation and fertilizer application is one of the main benefits from automated irrigation. In field crops, open field vegetables, and orchards, the controller activates simultaneously the water valves and the fertilizer injectors. In greenhouses, particularly when using detached beds, higher precision is required in synchronizing water and nutrient supply. For this end, dedicated controllers have been developed to control multi-nutrient supply, relying on monitoring of the chemical composition of the nutrient solution and the drainage water. Fig. 15.5. Fertilizer and Water Controller from "Gavish" brochure
- 243. 222 15.2.5. Integrated Monitoringand Control The highest level of control integrates monitoring of soil moisture, salinity and pH levels by sensors. All soil moisture sensors described above can be integrated with local or central controllers The central controller receives weather data from weather stations and the Internet. All the data are processed and used to adjust the preset irrigation program. Remote plots can be connected to the central computer by telephone, wireless radio transmitter or Internet. Fig. 15.6. Integrated Monitoring and Control Courtesy "Netafim"
- 244. 223 SPRINKLER IRRIGATION 1 6. M A I N T E N A N C E 1 6 . 1 . I n t r o d u c t i o n Operation of irrigation systems according to schedule facilitates optimal utilization of the equipment, efficient water use, and energy saving. Strict maintenance is requested to keep the system working and prevent decline in application uniformity. The performance of the system has to be routinely monitored in pre-designed time intervals. In addition to daily monitoring of the performance, periodical inspection of system components should be performed. 16.2. Installation Maintenance actually begins with system installation. Improper installation will cause troubles all over the system's life-span. 16.2.1. Mains and Sub-mains PVC pipes are sensitive to sunlight and must be installed within the soil, at least 30 cm deep. They are prone to be damaged by sharp edges of stones or when exposed to expansion and contraction of heavy and compacted soils. Therefore, before laying PVC pipes in a trench, it should be padded with sand. Right angles in the pipeline must be supported by concrete casting to prevent disintegration of the pipeline. 16.2.2. Laterals When connecting plastic laterals to manifolds, the barbed protrusion of the initial connector has to be fully inserted into the lateral to prevent the connectors from popping out in pressure surges. Laterals laid from reels, have to be positioned leveled on the ground for several hours before they are connected and stabilized. The delay is necessary to accommodate the lateral and release twisting formed in the reel package. Precise punching of holes in the lateral for insertion of the feeder tubes of micro-jets and micro-sprinklers requires dedicated tools, as shown in fig. 16.1. Fig. 16.1. Punch (left) and Holder (right) Courtesy "Netafim"
- 245. 224 SPRINKLER IRRIGATION In plotsprone to woodpecker activity, polyethylene laterals have also to be installed below the soil surface in order to be protected from punching by the birds. Before initializing the system, laterals, manifolds and pipelines have to be thoroughly flushed, to wash out all debris and soil particles that penetrated into the system during installation work. 16.3. Routine Inspection Routine inspections and preventive measures are necessary to guarantee appropriate performance of the irrigation system. The best maintenance policy is to inspect the whole system periodically and systematically. Time intervals between inspections depend on water quality and the attributes of the system components. Inspections can be performed weekly, monthly, or twice a year (in favorable conditions). 16.3.1. Pump Inspection In self-pumping installations, pump efficiency has to be tested at least once in 5 years. When water contains sand particles and/or the water is corrosive, the test should be performed bi-annually. Pump efficiency below 75% is economically undesirable in contemporary high energy costs. Low efficiency may indicate the deterioration of pump components that if are not repaired or replaced promptly, may terminate pumping. 16.3.2. System Performance Comparing the system’s actual measured flow-rate to the scheduled discharge provides preliminary indication of system performance. Deviation up to ±10% is normal. A flow-rate that is significantly lower than the scheduled discharge may indicate partial plugging of emitters or chocking of filters by dirt accumulation. A flow- rate significantly higher than the scheduled, may indicate burst of pipelines or punching of pipes and laterals and water leakage. Deviation from the scheduled flow- rate can also indicate changes in the pressure regime. The first step is to check the hourly flow-rate at the main flow meter and compare it with the designed flow-rate (number of emitters multiplied by the emitter’s nominal flow-rate). Second step - the pressure gauges that are installed in the plot have to be checked. The measured values have to be compared to the designed pressure for each set. The pressure difference between inlet and outlet and dirt accumulation in filters have to be checked as well. When too low flow-rate is noticed in an appropriate pressure regime, on-farm inspection of emitters' flow-rate uniformity should be performed. The minimum number of emitters per sample is 20. Once measured, the EU can be calculated and if it is unacceptable, the emitters should be cleaned with acid, flushed with pressurized air or replaced. The system should be checked again after treatment. Visual indicators of inadequate system performance are random stressed plants, surface runoff and white salt spots on the soil surface.
- 246. 225 SPRINKLER IRRIGATION 16.4 RoutineMaintenance 16.4.1. System Flushing and Cleaning Dirt, chemical precipitates and organic matter accumulate in the irrigation system during irrigation. Most of the dirt accumulates in the distal ends of laterals, manifolds and pipelines. Before the first irrigation in the season, the system has to be flushed thoroughly. For proper dirt removal, flushing of laterals has to be sequential, one after another, to keep the appropriate pressure and flow velocity in the open distal end. The lateral end plug or stopper is released and the dirty water is allowed to exit until clean water appears. Flushing velocities should be at least 0.5 to 0.6 m/s in order to remove effectively the dirt from the laterals. Lateral flushing can be accomplished automatically by automatic flushing valves installed in lateral ends. In this case, flushing takes place in the beginning of each irrigation in the time interval between water flow starts and the build-up of the operating pressure inside the lateral. Flushing has to be performed several times in the season. Intervals between flushing events depend on the rate of dirt accumulation. 16.4.2. The Control Head The control head components are sensitive to damage. Irrigation controllers have to be checked periodically for accuracy as well as to their responsiveness to commands from external sources. The control head is composed of different components. Malfunction of each of them may distort the performance of the irrigation system. 16.4.2.1. The Controller Today's controllers are sophisticated devices containing electronics, wiring and interfaces to the irrigation system. These components are prone to damage if not monitored and maintained thoroughly. It is recommended that the controller and the associated accessories (solenoids, pressure regulators, air release and relief valves, fertigation equipment, etc.) will be checked once a week. Wiring connections have to be checked for wear and breakage and repaired if necessary. If the Irrigation schedule is programmed on the field controller, once a month it will be checked for its relevance to the current conditions. Fig. 16.2. Automatic Lateral End Flushing Valve Courtesy "Netafim" Fig. 16.3. Control Head From Bermad brochure
- 247. 226 SPRINKLER IRRIGATION 16.4.3. TheIrrigation Network As mentioned before, the system has to be flushed periodically to release precipitates and debris accumulated in the pipes and the emitters. It can be done by unplugging the ends of laterals, allowing the water flow until no contamination is observed in the flow. If the lateral end is buried deep in the soil, water release can be done by removing the last emitter from its riser or supply tube. Broken emitters have to be replaced. Clogged emitters will be cleaned or replaced. Leaking valves have to be repaired or replaced. Leaking or broken pipes will be replaced. An indication for leakage can be the appearance of algae or moss on the soil surface adjacent to the leaking point or object. The system has to be monitored when irrigating, in order to observe excessive or too low working pressure. Excessive pressure is indicated by breakage of the water jet into spray. Too low pressure decreases the wetting range of the emitter. The emitters have to be the same and uniform in s simultaneously irrigating zone. Vegetation and other obstructions that may block adequate water distribution will be removed. The emitter Heads should be aligned vertically, except in sloped areas. In a sloped area, heads should be aligned perpendicular to the slope to achieve proper coverage. Tilted heads can cause ponding and uneven water distribution. The integrity of the pipeline system is a crucial factor in water use efficiency. Plastic pipes are damaged easily by rodents, woodpeckers, workers, mechanical tools and in some cases by extreme climate conditions - overheating of on-surface laterals or freezing of water inside the system. Another detrimental occurrence in pipelines and accessories is the precipitation of non-soluble salts from the irrigation water that reduce the cross section of the pipelines, increase friction head losses and may obstruct emitters. Precipitation affects more severely small-diameter laterals and low-volume emitters. Fig. 16.4. Coupling of PE Pipes Fig, 16.5. Replacing Seal Mechanical tools can damage aluminum pipes. The most sensitive component is the rubber seal in the coupler. These seals are prone to degradation and wear by hot and dry weather and the friction in the course of coupling and uncoupling. Rigid PVC / UPVC pipes are damaged by sunlight if they are not buried in the soil. Polyethylene pipes are prone to damage by animals and machines. Small plugs can fix small holes but in the case of bigger holes the pipe has to be cut and joined by a special coupler.
- 248. 227 SPRINKLER IRRIGATION Fig. 16.6.Insertion of Emitters In Small-diameter Soft PE Lateral Fig. 16.7. Components of Hydraulic and Metering Valves. The Wear-sensitive Components Wear in valves initially occurs to the flexible seals and the diaphragms in the hydraulic valves. In hydraulic valves the control tubes have to be checked for integrity and leakage. In filtering systems, the filtering elements have to be checked for integrity. In automatic back- flushed filtering systems, the control elements have to be tested for accuracy. The water emitters are prone to wear and malfunction. It should be taken into account that in mobile systems the water emitters are operated significantly more hours in the season than the emitters in solid-set systems. Hence the periodical checks in mobile systems have to be done more frequently. The most wear-sensitive components of the emitters are the flexible seals, the nozzles, the springs and the hammer. In water carrying sand, there will be accelerated wear of metallic nozzles while plastic nozzles are more resistant. Enlargement of the nozzle cross-section may cause increase in the flow-rate of the emitter and decrease in the distribution uniformity. In fertigation devices, the components that come in contact with the concentrated fertilizer solutions degrade with time and have to be frequently replaced. Fig. 16.9. Sprinkler Components Fig. 16.8. Sprinkler Tools
- 249. 228 SPRINKLER IRRIGATION 16.4.4. Micro-irrigationSystems The best system design cannot compensate for inadequate system maintenance. Micro-irrigation systems in particular, require careful and strict maintenance. The narrow water passageways in the emitters, the sensitivity of the filtration and fertigation devices, as well as the complexity of the monitoring and control appliances, require commitment to a meticulous maintenance policy. Fig. 16.10. Micro-jets and Mini-sprinklers Components 16.4.4.1. Maintenance of Micro-jets and Micro-sprinklers In mini-sprinklers and micro-emitters, solid contaminants and chemical precipitates may wholly or partially clog the water passage, lowering distribution uniformity. Malfunction of micro-jets and micro-sprinklers is easily noticed. The visual indications are changes in distribution patterns, an altered rotation rate in rotating emitters, stuck immobilized rotating and vibrating emitters and slanted stakes. Emitter-bearing stakes have to be positioned vertically. Stake bending impairs water distribution and may enhance run-off and water losses. Certain stakes are marked to indicate the depth of insertion required to stabilize the emitter vertically and to ensure the emitter's right height above soil surface for optimal water distribution. 16.4.5. Maintenance of Accessories The working environment of an irrigation system can be considered “hostile”. Chemical precipitations, friction-induced wear, corrosion and mucous excretions by microorganisms cooperate to distort system performance. In the framework of routine maintenance, the functioning level of discrete components has to be checked routinely. 16.4.5.1. Flow-meters have to be calibrated once in 2–5 years, depending on the volume of water delivered and concentration of solid contaminants in the water. 16.4.5.2. Hydraulic Valves that have an internal diaphragm. The integrity and flexibility of the diaphragm has to be routinely inspected. If necessary, the diaphragm should be replaced.
- 250. 229 SPRINKLER IRRIGATION 16.4.5.3. PressureRegulators - the operation mechanism is based on spring resistance or hydraulic equilibrium preserving. Springs are weakened after prolonged operation. They should be inspected once in two years and replaced if necessary. 16.4.5.4. Vacuum-relief Valves carry out an important function in irrigation systems. When the irrigation is turned- off, water remaining in the system flows downhill to the lowest outlets. The water vacating the high points creates a vacuum, which causes the emitters in this section of the plot to suck in air. In extreme cases, PVC mainlines may collapse. Vacuum-relief valves that are installed at the high points in the irrigation system, are prone to clogging and need periodic inspection to ensure that no solid objects are caught inside and that they are not stuck in an open or shut- off position. Air release valves also require the same periodic examination. 16.4.5.5. Filtration Equipment should be thoroughly inspected. In some filter types, the steel body is coated with epoxy paint to protect it from corrosion. The epoxy paint should be checked routinely. Cracks in the coating shorten the endurance of the entire body. The collectors of sand separators, should be purged periodically, otherwise excess accumulating sand will decrease separation efficiency. Screen filters should be disassembled and screens visually inspected for wear, tear and blockage by organic matter, silt and chemical precipitates. The same applies to disk filters. Manually cleaned filters will be serviced when the pressure difference between the inlet and outlet exceeds 5 m (0.5 bar). Automatic back-flushing filter systems require periodic visual inspection of the filtering elements for wear and presence of persistent contaminates. The back- flushing filter mechanism components: control hydraulic valves, solenoids and rotating brushes or vacuum suckers, may require periodic servicing and lubrication. Most of them include a small water filter to prevent blockage of solenoid ports and valve control chambers. These filters needs frequent manual cleaning. Automatic back-flushing media filters require special attention. They fluidize and resettle the filtering media with every flushing cycle. The discharge of back flushed media filters should be within the specified range of each model. For a typical 48" diameter tank, the range is 70 - 95 m3 /h, higher than the filtering capacity of 50 – 70 m3 . Below the lower margin, contaminants tend to infiltrate deeper into the media bed. Flow-rates higher than the recommended upper threshold can lead to coning and canalization of the filtering media. To effectively back-flush a filter, an adequate flow-rate is critical, particularly for sand filtering media. It should be large enough to fluidize and lift the filtering media, while pushing out just only a minor amount of sand through the flushing discharge manifold. Fig 16.11. Vertical Stake Fig. 16.12. Flow Regulator
- 251. 230 SPRINKLER IRRIGATION Media filtershave to be routinely inspected for checking the height of the filtering media in the tank. During the back-flushing process, a portion of the media is drained-off. When the void tank volume is greater than ⅓ of the total volume, the missing media should be replenished. 16.4.6. Maintenance of Fertigation Systems 16.4.6.1. Evaluating System Performance Excessive fertilization can induce salinity damage as well as antagonistic interference between nutrition elements. The precision of nutrient application can be checked in three procedures: a. Collecting water samples from the emitter laterals downstream from the injection point, and comparing the sample analysis with the desired concentration. b. Analyzing an extracted sample of soil solution. c. Analyzing the nutrient content of soil samples. 16.4.6.2. Maintenance of Chemicals Injection Devices The fertigation equipment is exposed to corrosive nutrient solutions. Metallic components like epoxy coated fertilizer tanks, injection pump components, control valves and pressure gauges corrode and should be replaced frequently. Some injection pumps have to be lubricated periodically. In diaphragm fertilizer pumps the diaphragm should be inspected for integrity and flexibility. Inflexible diaphragms will not perform effectively. 16.5. Chemical Water Treatments As mentioned before, chemical water treatments keep the system clean and running. They can be applied as a preventive measure or as a corrective treatment after the clogging occurred. Chemical treatments are particularly essential in micro-irrigation systems. In higher flow emitters systems they are required only in extreme low- quality water, like reclaimed and storm-water. The treatments can be classified into two groups: a. Acidification b. Oxidation 16.5.1. Acidification Acidification lowers water pH. This eliminates precipitation of insoluble salts of the cations calcium, magnesium, Iron and manganese with the anions bi-carbonate, carbonate, sulfate and phosphate. In low pH levels, the solubility of these salts is relatively high and the rate of precipitation is reduced significantly. The required concentration of the acid in irrigation water for attaining satisfactory results depends on the levels of bi-carbonates and sulfates in the water. The customary range is 0.5% - 1.5% in continuous acidification. Acid injection is used also to dissolute precipitates that clog emitters 16.5.2. Oxidation The dominating oxidizing agents are chlorine compounds. Oxidation is implemented for decomposing of sustained organic matter and preventing development of algae and colonies of microorganisms as persistent clogging factors.
- 252. 231 SPRINKLER IRRIGATION In micro-irrigationsystems irrigating with water containing organic matter, iron, sulfur and manganese, routine oxidation with chlorine is obligatory. Chlorination can be accomplished continuously with 2 – 5 ppm of active chlorine in the water or intermittently as “shock treatment” when the build-up of slime in the system is accelerated. “Shock treatment” with 15 – 30 ppm chlorine is applied for 20 – 30 minutes. When downstream of the injection point are installed devices with diaphragms, like some types of hydraulic valves and fertilizer injectors, an upper threshold of 15 ppm is suggested to prevent damage to the diaphragms. A fast on- farm test indicates if the applied chlorine amount was sufficient. If the measured residual chlorine level in the distal ends of the laterals is above 0.5 – 1 ppm, sufficient chlorine had been applied. Copper-sulfate is another oxidizing agent, particularly efficient in suppressing algae development in surface water reservoirs. 16.6. Overwintering of the Irrigation System At season end it is essential to accomplish some particular maintenance procedures to protect the system and ensure that it will be ready for the next irrigation season: 16.6.1. Entire System In micro-irrigation systems it is necessary to chlorinate the entire system. If sand filters are in use, they have to be backflushed first with water and then with injected liquid bleach (5% chlorine) at a concentration of 500 ppm. The minimum contact time at the farthest emitter will be 30 minutes. The irrigation system is shut down for 24 hours and then flushed sequentially, beginning with the filtration devices, then the mainline and the submain and finally, the lateras and the emitters. 16.6.2. Filtration Equipment The filters will be flushed and drained. Then the interior components of sand seperators, screen and disk filters will be inspected for wear, breakage, tear and corrosion. Seals, gaskets and valve seats have to be checked for integrity and flexibility. 16.6.3. Valves The valves will be completely drained. Dirt, corrosion residues and biologic slime and precipitates will be removed, gaskets and seals will be checked for integrity and flexibility and replaced when their condition is improper. 16.6.4. Controllers and Sensors The controllers and the sensors will be cleaned thoroughly. Batteries, if are in use, will be removed and stored, control panel seals will be checked and replaced if found improper. The hydraulic control tubes will be flushed and drained. Electrical conductors will be checked for integrity and functionality. Electrical wires will be disconnected. 16.6.5. Chemical Injection Equipment The Injection devices will be flushed and drained, the exterior surface will be cleaned. The coating will be checked and repaired if necessary, in coated tanks. Pumps and gear reducers will be lubricated, if required. Check-valves and back-flow preventers will be checked for functionality
- 253. 232 SPRINKLER IRRIGATION 16.6.6. Pumps Thepump will be drained of water. The suction pipes will be removed and stored. Grease and oil-lubricated bearings will be coated with lubricant. The shaft and other exposed metal components will also be coated with protective lubricant to prevent corrosion. Suction cover or volute of horizontal centrifugal pumps will be removed to check wear of rings and impeller, and to remove debris from impeller and volute. Packing gland will be removed to check wear on shaft sleeve. Then the pump will be repacked. 16.6.7. Electric Motors Dust, debris, and caked-on dirt and oil will be removed from the motor. The winding insulation will be inspected visually and all the bearings will be lubricated. The motor will be covered to protect it against rodents, insects and dust. Adequate ventilation will be kept in the motor storage vicinity to prevent condensation.
- 254. 233 SPRINKLER IRRIGATION 17. GLOSSARY Acid- A substance that has a pH lower than 7. (pH 7 is neutral). Specifically, an acid has more free hydrogen ions (H+ ) than hydroxyl ions (OH- ). Acidification - Increasing the acidity of a solution (including soil solution) by addition of hydrogen ions (in acids or acidic agents). Acre-foot - A volume of water that would cover one acre to a depth of one foot, or 325,850 gallons of water. Actuator - Device used to open/close or control the valve. Key types include electrical, hydraulic and pneumatic actuators. Movement may be quarter-turn or multi-turn. Actuators may be used when (i) valves are remotely located (e.g., on pipelines) (ii) valves are located in hazardous areas (iii) manual operation would be time-consuming (e.g., with larger valves). Adaptive plants - Non-indigenous plants that easily adapt to the climate and thus require little or no supplemental irrigation once established. Agricultural irrigation - Water distribution systems and practices in agriculture. Air gap - A backflow preventing technique of physical separation or maintaining air gap between two piping systems or hydraulic devices. Air valve – A Valve that is used to control the flow of air. Flows are normally small, so solenoid valves are suited. Alkaline - Water or soil that contains an amount of alkali (strongly basic) substances sufficient to raise the pH value above 7.0 and disturb growth of crops. Alkalinity - the capacity of water for neutralizing an acid solution. Allowable Water Depletion (AWD) - The percentage from Plant Available Water (PAW) that can be depleted from the active plant root zone before irreversible damage is brought about to the plant. American National Standards Institute (ANSI) - An association involved in developing standards for a wide range of products used in water supply and irrigation. American Society of Mechanical Engineers (ASME) - A professional organization whose Codes and Standards Committee helps to write and publish ANSI standards. American Water Works Association (AWWA) - A professional organization serving the irrigation and drinking water supply profession. Ampere or Amp. - A unit of electrical current. The unit is used to specify the movement of electrical charge per unit time through a conductor. Angle valve - A valve configured with its outlet oriented 90 degrees from its inlet. Anti-siphon valve - A control valve with a built-in atmospheric vacuum breaker. Application efficiency - The ratio of the average depth of irrigation water infiltrated and stored in the root zone to the average depth of irrigation water applied, expressed as percentage unit. Application rate - The amount of water delivered to a given area per time unit, typically expressed in mm/h.
- 255. 234 SPRINKLER IRRIGATION Applied water- Water applied by irrigation, usually expressed as a depth of water in mm or as m3 /Ha. Aquaculture - Farming of plants and animals that live in water, such as fish, shellfish, and algae. Aqueduct - A pipe, conduit, or channel designed to transfer water from a remote source, usually by gravity. Aquifer - A geological formation or structure that stores and/or transmits water, such as to wells and springs. Aquifer (confined) - Soil or rock below the land surface that is saturated with water. There are layers of impermeable material both above and below it and it is under pressure so that when the aquifer is drilled for well, the water will rise above the top of the aquifer. Synonym: artesian aquifer. Aquifer (unconfined) - An aquifer whose upper water surface (water table) is at atmospheric pressure, and thus is unable to rise and fall. Arable - Land having soil properties and topographic features suitable for cultivation. ARC - Describes how far around in a circular pattern a sprinkler will rotate or spray. (A sprinkler with a 90°arc would distribute water in a quarter circle pattern.) Arid - A climate characterized by less than 250 mm of annual rainfall. Artesian water - Ground water that is under pressure when tapped by a well and is able to rise above the level at which it is first encountered. It may or may not flow out at ground level. The pressure in such an aquifer commonly is called artesian pressure, and the formation containing artesian water is an artesian aquifer or confined aquifer. Artificial recharge - A process where water is returned into groundwater storage from surface-water supplies such as irrigation, or induced infiltration from streams or wells. Artificial recharge - The intentional addition of water to an aquifer. As-built plan - An updated plan of an installed irrigation system designating valve, sprinkler and controller locations, routing of pipe and control wires. The plan includes all changes to the original design that were completed during installation. Atmospheric Vacuum Breaker (AVB) - A backflow prevention device that introduces air into the irrigation system when the system pressure drops to atmospheric pressure or below, to prevent back siphonage. Automatic valves - These valves enable presetting the desired water amount to be applied. Presetting can be done manually or by remote controller. Automatic control valve - An irrigation valve which can be remotely operated. The remote operation method may be either electrical (the most common) or hydraulic. Automatic valves are commonly used as "control valves" for irrigation systems. Available Water-Holding Capacity (AWHC) - The amount of water held in the soil that is available to the plants. Back pressure - Increase of pressure in the downstream piping system above the supply pressure at the point of connection which would cause, or tend to cause, a
- 256. 235 SPRINKLER IRRIGATION reversal ofthe normal direction of flow. Back siphonage - Reversal of water flow due to pressure reduction upstream, which generates a negative or sub-atmospheric pressure below the downstream pressure in the system. Backflow preventer - A safety device installed between the point of connection between the water supply network and the irrigating network that is designed to prevent the backflow of contaminated water into the potable water supply line. Typically used in conjunction with automatic irrigation systems. Types of backflow preventers include: Air Gap. Atmospheric Vacuum Breaker (AVB). Double Check (DC), Pressure Vacuum Breaker (PVB), Reduced Pressure (RP, RPA, RPZ). Backflow - Reverse flow of water in a piping system. Back-flush - The reverse flow of water, through a filter or filtration media, used for removing solids accumulated during the filtration process. Ball valve - A quarter-turn valve with a spherical closing element held between two seats. Base - A substance that has a pH higher than 7. A base has less free hydrogen ions (H+) than hydroxyl ions (OH-). Bedrock - The solid rock beneath the soil and superficial rock. A general term for solid rock that lies beneath soil, loose sediments, or other unconsolidated material. Bellows - Sealing device which prevents line media leaking between the stem and the body of the valve. Benefit-cost ratio - Benefits and costs measured in terms of money and expressed as a ratio, with benefits divided by costs; typically used as an evaluation tool for different water efficiency increasing measures and programs. Best Management Practice (BMP) - A set of practices, measures or procedures that are beneficial, empirically proven, cost effective, and widely accepted by the professional community. BOD - Biological Oxygen Demand or Biochemical Oxygen Demand is a procedure, used in water quality management, for determining how much biological organisms use up oxygen in a body of water. Booster pump - A pump installed in the mainline inlet for increasing the pressure in the irrigation system when the pressure in the supply system is not high enough. Brackish water - Brackish water is water with a level of salinity between freshwater and seawater. Brackish water contains between 0.5 and 3 grams of salt per liter. Bubbler - A water emission device that applies water directly to the soil surface, or that throws water a short distance, up to 30 cm, before water contacts the soil. Bulk density - Mass per unit volume of undisturbed soil, dried to constant weight at 105 degrees C0 expressed as g/ml. Butterfly valve - A quarter-turn valve which has a circular disk as its closing element. By-Pass valve - A small bore valve fitted in parallel to a larger main valve. Bypass
- 257. 236 SPRINKLER IRRIGATION valves areused to reduce the differential pressure across the main valve before this latter valve is opened (as otherwise this larger, more expensive valve, may suffer damage to internal components). Capillarity - Moisture movement in the soil in any direction through the fine pore spaces and as films around particles. The water is drawn into small diameter virtual tubes by the adhesive forces between the liquid and the tube walls. Capillary action - The means by which liquid moves through the porous spaces in a solid, such as soil, plant roots, and the capillary blood vessels in our bodies due to the forces of adhesion, cohesion, and surface tension. Capillary action is essential in carrying substances and nutrients from one place to another in the soil, in plants and in animals. Catch-can test - A measurement of precipitation from a sprinkler system in which water is collected in graduated containers (catch-cans) placed in the irrigated area at evenly spaced intervals for a specific period of time. Central irrigation control - A computerized system that controls local irrigation zones from a centralized location using a computer. Check-valve - A small device allowing water to flow in one direction only. Types include swing check, tilting disc check and wafer check. Check valves (also called non-return valves) are usually self-acting. Chemigation - Application of chemicals like fertilizers, disinfectants, oxidizers, acidifiers, soil amendment agents and pesticides through the irrigation system. Clogging – (1) The accumulation of solids on a filter media that block it, resist the water flow through the filter and increase the differential pressure. (2) Accumulation of precipitates and solids in the water passages of emitters, blocking fully or partially the water flow. COD - Chemical Oxygen Demand - A water quality test that indirectly measures the amount of organic compounds in water (expressed in mg/l). Coefficient of uniformity (Cu) - A measure of the uniformity of water distribution in a defined surface area, from emitters that deliver water through the atmosphere expressed as percentage. Using a catchment test in an irrigated area, the CU is a comparison of the average precipitation of all catchments and the deviation from that average. (A perfect CU of 100 states that the system is very efficient and there is no variability in water distribution). Condensation - The process of turning water vapor in the air into liquid water. Water drops on the outside of a cold glass of water are condensed water. Condensation is the opposite process of evaporation. Consumptive use - That part of water withdrawn that is evaporated, transpired by plants, incorporated into products or crops, consumed by humans or livestock, or otherwise removed from the immediate water environment. Also designated as crop requirement, crop irrigation requirement, and consumptive use requirement. Control valve - A valve which regulates the flow and/or pressure of a fluid. Control valves normally respond to signals generated by independent devices such as flow meters, temperature gauges, etc. Control valves are normally fitted with actuators and positioners. Conveyance loss - Water that is lost in transit from a pipe, canal, or ditch by leakage
- 258. 237 SPRINKLER IRRIGATION or evaporation.Generally, the water is not available for further use; however, leakage from an irrigation ditch, for example, may percolate to a ground-water source and be available for further use. Cost-effectiveness - A comparison of total benefits against total costs. Crop coefficient (Kc) - The decimal fraction designating the ratio between a specific crop water requirement and the reference evapo-transpiration Et0. Cycle and soak capability - A feature in some types of controllers that allows the controller to divide up station run time, allowing the soil sufficient time to absorb the water before continuing irrigation. Cycle – (1) The time duration of irrigation of one irrigated zone. (2) One complete operation of a controller station. Debris - Organic and inorganic suspended solids collected on the filter element. Quantity of debris is usually expressed in PPM. Size of the particles usually expressed in micron. Deep percolation - The vertical movement of water downward through the soil profile, below the root zone caused by gravity. Demand forecast - A projection of future water use. Demand scheduling - Method of irrigation scheduling whereby water is delivered to users as needed and which may vary in flow-rate, frequency and duration. Considered a flexible form of scheduling. Density - Density of a body is the ratio of its mass to its volume - A measure of how tightly the matter within the body is packed together. Depth filtration - Removing and retaining suspended solids by means of their interception and adhering to grains or fibers (filtration media). Desalination - The removal of salts from saline water to provide freshwater. This method is becoming a more popular way of providing freshwater to populations. Design capacity - Measured in m3 /h, the “design capacity” is the maximum amount of water available for use in an irrigation system. The available design capacity determines how many emitters may be in operation at the same time. Design emission uniformity - The anticipated emission uniformity relating to the emitter’s Cv and the expected pressure variation. Design pressure - The minimum pressure required for proper operation of an irrigation system. Diameter of coverage - Average diameter of the area wetted by emitter spreading water through the atmosphere in wind-less conditions. Diaphragm valve - A bi-directional valve which is operated by applying an external force to a flexible element, or diaphragm (typically made of an elastomer). Diaphragms - Flexible membranes in automatic valves, fertilizer injectors and compensating emitters that regulates the passage of water through the device. Differential pressure - The difference in pressure between upstream (inlet side of the filter) and downstream (outlet side of the filter). DIN - The German Institute for Standardization (Deutsches Institut fur Normung e.V.);
- 259. 238 SPRINKLER IRRIGATION this instituteestablishes standards for testing and classifying irrigation equipment. Discharge - The volume of water that passes a given location within a given period of time. expressed in l/h or m3 /h. Distribution efficiency - Measure of the uniformity of irrigation water distribution over a field. Distribution system - A system of pipes and valves that conveys water from a treatment plant to end users. Distribution Uniformity (DU) - The evenness with which water is distributed over an irrigated area. DU is calculated using a catchment test or emitters sample discharge test. The average reading of the lowest one-quarter of catchments/emitter flow-rated is devided by the average reading of all measurements, and multiplied by 100. An excellent DU percentage is 75% to 85%, while a good DU is 65% to 70%. Ditch - A constructed open channel for conducting water. Diversion structure - A channel constructed across the slope for the purpose of intercepting surface runoff; changing the accustomed course of all or part of a stream. Diversion of water - Removal of water from its natural channels for human use. Diverter valve - A valve which can change the direction of the flow of a fluid to two or more different directions. Double block and bleed - A valve configuration in which positive shut-off is achieved at both the inlet and outlet sides. A small port is fitted to discharge fluid in the intermediate space. Double Check Valve (DCV) - A device containing two independent, inline, positive seating, spring loaded check valves, two shut-off valves and ball valve test cocks. Drain valve, automatic - Spring loaded valve that will automatically open and drain the line when the pressure drops to near zero. Drainage basin - Land area where precipitation runs off into streams, rivers, lakes, and reservoirs. It is a land feature that can be identified by tracing a line along the highest elevations between two areas on a map, often a ridge. Large drainage basins may contain thousands of smaller drainage basins. Also called a "watershed." Drainage - The process of removing surface or subsurface water from a soil or land area. Draw down - The depth (from the top of the well) to the water surface in a well when the pump is operating. The lowering of the ground-water surface caused by pumping. The water level typically drops when the pump is running. Drip irrigation - A type of micro-irrigation systems that delivers water in slow drips to plants through a network of plastic pipes and emitters. Drip irrigation is a low pressure method of irrigation and less water is lost to evaporation than in high- pressure sprinkler irrigation. Drought - A period of dryness and insufficient soil moisture that causes extensive damage to crops and prevents their successful growth. Drought condition - The hydrologic conditions during a defined drought period in which rainfall and runoff are significantly lower than average.
- 260. 239 SPRINKLER IRRIGATION Dynamic pressure- Measure of water pressure when the water is in motion (also designated working pressure). Effective filtration area - The Total Area of the Filter Medium which is exposed to flow and is usable for the filtration process. Effective precipitation - The total depth of rainfall minus the volume lost to evaporation and leaching during a specific time period. Effluent - Wastewater, treated or untreated, that flows out of a treatment plant, sewer, or industrial outfall. Electric actuators - Actuators activated by an electric motor to operate the valve stem. Electric valve - Automatic valve controlled by 24 to 30 volt (AC) current. Electrical Conductivity (EC) - An indicator to the concentration of soluble salts in water and soil solution. Elevation gain - Pressure gained as water flows downhill from its source or a reference point. Elevation head - The fraction of measured head (pressure) derived from the topographic position. Emitter - The ingredient of the irrigation system that delivers water at a predictable rate. Encrustation (soil surface sealing) - The phenomenon in which the surface of a soil is compacted, dispersed and rearranged by the impact of raindrops. Although the surface seal is only few mm thick it significantly reduces the infiltration rate of water. End-user - A consumer of water; a utility water customer. Environment - The sum of all external factors and conditions affecting the life and development of organisms or ecological communities. Erosion - The removal of soil particles from soil surface by weathering, running water, moving ice, wind and mass movement. Evaporation - the process of liquid water becoming water vapor, including vaporization from water surfaces, land surfaces, and snow fields, but not from leaf surfaces. Evapotranspiration (ET) - The amount of water consumed by a crop is the sum of the amount lost through the evaporation of moisture at the soil’s surface and the transpiration of the water through the plants. The daily evapotranspiration rate, or ET is used in scheduling the irrigation needs for growing plants. This value is calculated from measured climatic factors such as temperature, solar radiation, humidity, wind, time of year, precipitation, etc. Fallow - land plowed, tilled and left unplanted. Faucet aerator - a device that can be installed in a sink to reduce water flow-rate by mixing air with the water. Faucet restrictor - a device inserted into a faucet that forces water through a smaller orifice for the purpose of reducing the flow-rate. Field Capacity (FC) - The percentage, per weight or per volume of the water
- 261. 240 SPRINKLER IRRIGATION retained inthe soil after irrigation or rain, when the rate of downward movement has substantially decreased, usually one to three days after irrigation or rain ended. Filter area - The total area of a filtration element, usually expressed in square centimeters or square inches. Filter cake - The debris accumulated on the filter element, blocking it, resist the water flow through the filter and increase the differential pressure. Filter - A device which removes particles from water by means of a physical barrier, chemical process and/or biological process. Filtration degree - Size of pores in filtration medium (expressed in mm, micron or mesh units). Filtration element - The active component of the filter, it determines the type of filter and the filtration level. Filtration velocity - Flow-rate per cross section area [m/hr]. Filtration - The process of removing solid particles from fluid by forcing them through a porous medium. Flange - A flat metal ring with a hole in its center, through which a pipe passes, and with a number of smaller holes drilled circumferentially, destined for the connecting bolts. Float valve - A valve which automatically opens or closes as the level of a liquid changes. The valve is operated mechanically by a float which rests on the top surface of the liquid. Flood - An overflow of water onto lands that are used or usable but are not covered normally by water. Floods have two essential characteristics: The inundation of land is temporary; and the land is adjacent to and inundated by overflow from a river, stream, lake, or ocean. Flood Irrigation - A method of irrigating with water that is applied from field ditches onto land that has no guide preparation such as furrows, borders or corrugations. Flow - The movement of fluids, through pipe, fittings, nozzles, valves or other vessels. Measured in Cubic Meters Per Hour (m3/h), Liters Per Minute (l/m), Liters Per Second (l/s), Gallons Per Minute (GPM), Gallons Per Hour (GPH), Cubic Feet Per Second (ft3 /s). Flowing well/spring - a well or spring that taps ground water under pressure so that water rises without pumping. If the water rises above the surface, it is known as a flowing well. Flow-rate - The amount of water moving through an emitter, a pipe, fixture, stream, etc. Volume of water per unit of time, measured in l/h or m3 /h. Flush-flow - High initial momentary flow through an irrigation lateral; required to flush the lateral and emitters before the working pressure is built-up. Freshwater - Water that contains less than 1,000 milligrams per liter (mg/l) of dissolved solids. More than 500 mg/L of dissolved solids is undesirable for drinking and many industrial uses. Friction-loss - The pressure lost as water flows through pipes, fittings and valves of an irrigation system. As the velocity of water flowing through the system increases,
- 262. 241 SPRINKLER IRRIGATION the friction-losseswill also increase. These losses, measured or calculated, can be used to estimate the approximate dynamic (working) pressure at any given point of a system. Full-bore - Term used to indicate that the internal diameter of the valve opening is the same as that of the piping to which it is fitted. Gage - Device for registering water level, discharge, velocity, pressure, etc. Gage height - The height of the water surface above the gage datum (zero point). Gage height is often used interchangeably with the more general term stage, although gage height is more appropriate when used with a gage reading. Gaging station - A site on a stream, lake, reservoir or other bodies of water where observations and hydrologic data are obtained. Gate (irrigation): structure or device for controlling the rate of flow into or from a canal or ditch. Gate valve - A multi-turn valve which has a gate-like disk and two seats to close the valve. Gated pipe - Portable pipe with small gates installed along one side for distributing irrigation water to corrugations or furrows. Gauging station - Specific location on a stream where systematic observations of hydrologic data are obtained through mechanical or electrical means. Gearboxes – (1) Used to ensure easier operation of larger valves, particularly ball valves. (2) Used in Center-Pivot and Linear-Move systems to deliver power to wheels. Globe valve - A multi-turn valve configured with its outlet oriented 180 degrees from its inlet but having flow path with directional changes and a gasketed disk moving perpendicular to the flow path to open or close the valve. The closing element seals in a plane parallel to the direction of flow. This type of valves is suited both to throttling and general flow control. GPM (Gallons per Minute) - A standard measurement of water flow in the imperial unit system. The available GPM (also known as design capacity) must be known before a sprinkler design can be completed. Sprinklers have different GPM requirements. The total GPM of all of the sprinklers on one zone should not exceed the available GPM capacity. Gravity flow - A water system that relies on gravity to provide the driving force required to deliver the water. Consists of a water source located at a higher elevation than the water delivery points. Gray water: domestic wastewater composed of wash water from kitchen sinks, bathroom sinks and tubs, clothes washers, and laundry tubs that can be used for non-potable purposes such as irrigation. Ground water - (1) Water that flows or seeps downward and saturates soil or rock, supplying springs and wells. The upper surface of the saturate zone is called the water table. (2) Water stored underground in rock crevices and in the pores of geologic materials that make up the Earth's crust. Ground water, confined - ground water under pressure significantly greater than atmospheric, which its upper limit is the bottom of a bed with hydraulic conductivity
- 263. 242 SPRINKLER IRRIGATION distinctly lowerthan that of the material in which the confined water occurs. Ground water, unconfined - Water in an aquifer that has a water table that is exposed to the atmosphere. Groundwater mining (overdraft) - Pumping of groundwater for irrigation or other uses, at rates faster than the rate at which the groundwater is being recharged. Groundwater recharge - The flow to groundwater storage from precipitation, infiltration from streams, and other sources of water; the use of reclaimed wastewater, by surface spreading or direct injection, to prevent saltwater intrusion into freshwater aquifers, to store the reclaimed water for future use, to control or prevent ground subsidence, and to augment non-potable or potable ground water aquifers. Groundwater table - The upper boundary of groundwater where water pressure is equal to atmospheric pressure, i.e., water level in a bore hole after equilibrium when groundwater can freely enter the hole from the sides and bottom. Hardness - A water-quality indication of the concentration of alkaline salts in water, mainly calcium and magnesium compounds. If the water used is "hard", the rate of precipitates formation and emitter clogging is enlarged. Head feet (pressure) - A measure of pressure expressed in feet of water. Equivalent to .433 PSI per foot of water. Head-to-head - Correct placement of sprinklers. One sprinkler must be placed so that it will overlap another sprinkler (or 50% of the adjusted diameter). This provides for uniform coverage of the irrigated area. Horticultural practices - Activities to maintain crops, such as irrigation, fertilization, mowing, plant protection and weed control. Hydraulic actuator - A device fitted to the valve stem using hydraulic energy to open and close the valve. Depending on the configuration, the hydraulic fluid may both open and close the valve, or just open the valve. In that latter case, a spring will typically be fitted inside the actuator to return it and the valve to the closed position. Hydraulic conductivity - The rate at which water will move through soil in response to potential gradient. Hydraulic valve - Valve which uses small flexible tubes and water under pressure to provide the actuation signal from the controller to the valve. Hydrologic cycle - The cyclic transfer of water vapor from the Earth's surface via evapo-transpiration into the atmosphere, from the atmosphere via precipitation back to earth, and through runoff into streams, rivers, and lakes, and ultimately into the oceans. Hydrology - The science dealing with the properties, distribution, and flow of water on or in the earth. Impermeable layer - A layer of solid material, such as rock or clay, which does not allow water to pass through. Infiltration - flow of water from the soil surface into the subsurface. Infiltration (intake) rate - The dynamic rate at which irrigation or rain water applied to the soil surface will move into soil depth, expressed as a depth of water per unit of
- 264. 243 SPRINKLER IRRIGATION time inmm per hour. The rate declines proportionally to the square root of time elapsed from the initial phase of surface hydration. Injection well - A well constructed for the purpose of injecting treated wastewater directly into the ground. Wastewater is generally forced (pumped) into the well for dispersal or storage into a designated aquifer. Injection wells are generally drilled into aquifers that don't deliver drinking water, unused aquifers, or below freshwater levels. In-line filter - A filter assembly in which the inlet, outlet and filter element axes are in a straight line. Interception - The pattern and amount of precipitation that does not reach the soil surface due to blocking by the vegetation. Irrigation - The controlled application of water for agricultural purposes through manmade systems that supply water requirements not satisfied by rainfall. Irrigation audit - An on-site evaluation of an irrigation system to assess its water-use efficiency as measured by distribution uniformity, irrigation schedule, and other factors. Irrigation cycle - A scheduled application of water by an irrigation system with a defined start time and duration. A cycle may include multiple watering zones. Irrigation Efficiency (IE) - The ratio of the average depth of irrigation water that is beneficially used to the average depth of irrigation water applied, expressed in percentage units. Beneficial uses include replenishment of soil water deficit and any leaching requirement to remove salts from the root zone, as well as freeze and hot spell protection. Irrigation plan - A two-dimensional drawing/plan that illustrates the layout of an irrigation system. Irrigation scheduling - Careful planning of irrigation application rates and timing to irrigate efficiently. Irrigation timer - a device that can be programmed to regulate the time and duration of irrigation; employs a clock mechanism. Irrigation water requirement - A measure of the water required in addition to precipitation to obtain desired crop yield. Irrigation water use - water application on lands to optimize the growing of crops and pastures or vegetative growth in recreational lands, such as parks and golf courses. Irrigation - application of water to land for the purpose of growing plants. Isolation valve - A valve used for isolating all or part of an irrigation system for repairs, maintenance, or winter shut-down (winterization). Common types of isolation valves are the ball valve, butterfly valve, and gate valve. Kilowatt-hour (kWh) - a unit of electric power equivalent to the energy provided by one thousand watts acting for one hour. Laminar flow - Fluid flow that is characterized by straight flow lines in constant direction. In pipes it can be regarded as a series of liquid cylinders in the pipe, where the innermost ones are the fastest, and those near the pipe wall are the slowest. Mostly happens in low flow velocities.
- 265. 244 SPRINKLER IRRIGATION Leaching -The process by which soluble materials in the soil, such as salts, nutrients, pesticide chemicals or contaminants, are washed into a lower layer of soil or are dissolved and carried away by water. Leaching Requirement (LR) - the quantity of irrigation water required for removal of salts from the root zone to maintain a favorable salt balance for plant development. Leak detection - Systematic methodology for identifying water leakage from pipes, plumbing fixtures, and fittings. Lentic waters - Ponds or lakes (standing water). Levee - A natural or manmade earthen barrier along the edge of a stream, lake, or river. Land alongside rivers can be protected from flooding by levees. Lift check - This non-return valve design incorporates a piston to damp the disk during operation. Line blind - A pipeline shut-off device, whereby a flat disk is forced between two flanges. Line blinds are less expensive than valves, but require much more time to operate. Looped circuit - A piping system, usually a main line, that closes back on itself in a loop, providing more than one path for the water to flow to the valve(s). Low head drainage - Water left in the pipe after a valve is turned off that is gently flowing out of a low elevation emitter. Low-water-using plants - Plants that require less than 30% of reference ET to maintain optimum health and appearance. Lysimeter - An isolated block of soil, usually undisturbed and in situ, placed in a container, for measuring the quantity, quality, or rate of water movement through or from the soil. Mainline - Pressurized pipe running from the point of connection to the zone control valves. Manifold – (1) A distributing pipe for laterals, starting out from the main or sub-main. (2) A short pipe segment with multi-oulets for fittings and valves. Master valve - A normally closed (NC) valve installed at the supply point of the mainline that opens only when the automatic system is activated. Matched precipitation rate - A system or zone in which all the emitters have similar precipitation rates is said to have matched precipitation rates. Maximum Allowed Depletion (MAD): The fraction of plant available water (PAW) that may be depleted from the active plant root zone without inducing stress to the plant. Maximum Contaminant Level (MCL) - The designation given by the U.S. Environmental Protection Agency (EPA) to water-quality standards promulgated under the Safe Drinking Water Act. The MCL is the greatest amount of a contaminant that can be present in drinking water without endangering human health. Media filtration (depth filtration) - A thick layer of graded particles such as sand, gravel or other granular materials contained inside filter housing and perform the filtration of water. The filtration rate depends on the effective size of the bedding and
- 266. 245 SPRINKLER IRRIGATION the watervelocity through the filter. Medium-water-using plants - Plants that require 30% - 50% of reference ET to maintain optimum health and appearance. Megawatt - One million watts; a measure of power-plant output. Mesh - The number of wires in a linear inch of a screen element. Meter - An instrument that measures the volume of water delivered. Microclimate - Climate conditions in limited area that differ from the typical climate prevalent in the surrounding area. Micro-irrigation - Irrigation technology employing small, closely spaced emitters to apply small amounts of water at low pressure. Micron - One millionth of a meter; known also as a micrometer (µm). Clogging particle size is usually expressed in microns. Micro-sprayers - Inclusive designation of micro-jets, spinners, rotators, ray-jets, misters and foggers. Micro-sprinklers - Miniature sprinklers discharging water in flow-rate range of 20 – 200 l/hour. Milligrams per liter (mg/l) - A unit of the concentration of a constituent in water or wastewater. It represents 0.001 gram of a constituent in 1 liter of water. It is approximately equal to one part per million (ppm). Mini-sprinklers- Small sprinklers discharging water in flow-rate range of 120 – 500 l/hour. Mulch – (1). Organic material (typically leaves, bark, wood chips, straw, compost), applied to the soil surface to protect soil from raindrop impact, improve infiltration of rain, reduce runoff, evaporation from soil surface and soil temperature fluctuations. (2). Plastic sheets used to cover the soil surface for isolating the crop from the soil surface or to facilitate efficient soil fumigation under the sheets. Multi-layer screen - A combination of selected ratios of weave type screens augmenting the mechanical strength. Multi-ported - Multi-ported valves include additional inlet/outlet ports, to allow fluids to be directed. The ball and plug valve types are ideally suited to multi-port designs. Multi-turn - Category of valves (such as gate, globe, and needle) which require multiple turns of the stem to change the valve position from the fully open to the fully closed position. Also known as linear valves. Needle valve - This multi-turn valve derives its name from the needle-shaped closing element. The design resembles that of the globe valve. Available in small sizes, often used on secondary systems for on/off applications, sampling, etc. Nephelometric Turbidity Unit (NTU) - Unit of measure for the turbidity of water. A measure of the cloudiness of water as measured by a nephelometer. Turbidity characterizes the amount of light that is reflected off particles in the water. Neutron probe - An instrument used to estimate soil moisture by measuring the rate of attenuation in pulsated neutron emissions that depends on soil water content. Non-consumptive water use - water withdrawn for use but not consumed and thus
- 267. 246 SPRINKLER IRRIGATION returned tothe source. Non-Point Source (NPS) pollution - Pollution discharged over a wide land area, not from one specific location. These are forms of diffuse pollution caused by sediment, nutrients, organic and toxic substances originating from land-use activities, which are carried to lakes and streams by surface runoff. Non-point source pollution is contamination that occurs when rainwater, snowmelt, or irrigation washes off plowed fields, city streets, or suburban backyards. As this runoff moves across the land surface, it picks up soil particles and pollutants, such as nutrients and pesticides. Non-volatile memory - A feature in irrigation controllers that will retain the programmed information in electronic memory during a power failure, without the need for a battery. Normally Closed (NC) valve - An automatic valve through which no water will flow unless external actuation is applied that trigger the valve to open. Most electric valves are of the normally closed type. Normally Open (NO) valve - An automatic valve through which water will flow unless external actuation is applied to close the valve. Most hydraulic valves are of the normally open type. Nozzle - The final orifice through which water is emmited from the emitter to the atmosphere. Open area - The Pore Area of the filter medium; expressed often as a percentage of its total area. Operating pressure - The pressure at which a device or irrigation system is designed to operate. Organic Matter (OM) - Plant and animal residues, or substances generated by living organisms. All are based upon carbon compounds. Orifice - Discharge hole in an emitter or lateral. Osmosis - The movement of water molecules through a thin membrane. The osmosis process is one method of desalinating saline water. Outfall - The place where a sewer, drain, or stream discharges; the outlet or structure through which reclaimed water or treated effluent is finally discharged to a receiving water body. Oxygen demand - The need for molecular oxygen to meet the needs of biological and chemical processes in water. Even though very little oxygen is dissolved in water, it is extremely important in biological and chemical processes. Ozonation - The process of applying ozone (O3 ) to a liquid for disinfection purpose. Pan evaporation - Evaporative water losses from a standardized pan used to estimate crop evapo-transpiration and assist in irrigation scheduling. Particle size - The diameter, in millimeters, of suspended sediment or bed material. Particle-size classification is: [1] Clay—0.00024-0.004 millimeters (mm); [2] Silt—0.004-0.062 mm; [3] Sand—0.062-2.0 mm; [4] Gravel—2.0-64.0 mm.
- 268. 247 SPRINKLER IRRIGATION Particle sizedistribution - Defines which part of the TSS (Total Suspended Solids) is relevant to the desired filtration degree; Number Density or Volume Density. Parts per billion (ppb) - The number of "parts" by weight of a substance per billion parts of water. Used to measure extremely small concentrations. Parts per million (ppm) - The number of "parts" by weight of a substance per million parts of water. This unit is commonly used to represent pollutant concentrations. Pathogen - A disease-inducing agent; usually applied to a living organism. Actually, any virus, bacteria, or fungi that cause disease. Peak demand - The highest total water use experienced by a water system. Penstock valve - A type of simple gate valve, used to contain fluids in open channels. Found in wastewater treatment plants. Percent area wetted - The area wetted by irrigation as a percentage of the total area in the plot. Percolation - (1) The movement of water through the voids in rock or soil. (2) The penetration of a portion of the stream-flow into the channel substratum to contribute to ground water replenishment. Percolation rate - (1) The rate at which water moves through porous media, such as soil; and (2) intake rate used for designing wastewater absorption systems. Permanent Wilting Point (PWP) - The amount of water in the root zone, as percentage of the soil weight or volume at or below which the plant will permanently wilt without recovery. Permeability - The capacity of a material to allow the passage of a liquid, such as water through. Permeable materials, such as gravel and sand, allow water to move quickly through them, whereas un-permeable material, such as clay, doesn't allow water to flow freely. pH - A measure of the relative acidity or alkalinity of water, soil solution and other liquids. The term designates the minus log of the hydrogen ions concentration. Water with a pH of 7 is neutral; lower pH levels indicate increasing acidity, while pH levels higher than 7 indicate increasingly basic solutions. Pilot valve - Small valve requiring little operating power which is used to activate a larger valve, mainly by means of solenoid. Pinch valve - A valve in which a flexible hose is pinched between one or two moving external elements to stop the flow. This valve is often used in slurry and mining applications, as its operation is not affected by solid particles in the medium. Pipe dope - Common name for commercial products used to apply to pipe fittings to assist in the appropriate fit of the threaded joints. Pitot tube - A small L shaped tube which can be attached to a pressure gauge or other measuring device to measure the velocity head of water discharging from a nozzle. Plant Available Water (PAW) - The amount of water held within the root zone after gravitational drainage has finished, minus the amount of water that adheres tightly to soil particles (that is defined as the Permanent Wilting Point).
- 269. 248 SPRINKLER IRRIGATION Plant waterrequirement - The amount of irrigation water needed to replace moisture depleted from the plant's root-zone as a result of evapo-transpiration and deep percolation. Plug valve - This multi-turn valve derives its name from its rotating plug which is the closing element. The plug may be cylindrical or truncated. In the open position, the fluid flows through a hole in the plug. Lubricated plug valves rely on a sealing compound injected between the plug and the valve body, whilst sleeved plug valves are fitted with a ‘soft’ insert between the plug and the body. Pneumatic actuator - A device fitted to the valve stem that uses pneumatic energy to open/close or regulate the valve. Depending on the configuration, the compressed air may both open and close the valve, or just open the valve. In that latter case, a spring will typically be fitted inside the actuator to return the valve to the closed position. Point of Connection (P.O.C.) - Location where irrigation system is connected to a potable water supply network. Point-source pollution - water pollution coming from a single point, such as a sewage-outflow pipe. Poly-pipe - Black, flexible Polyethylene pipe used as a lateral in areas susceptible to long freezes in the winter. Soil moves as it freezes, squeezing the pipe. Due to the poly-pipe flexibility, it will hold up to this movement while the more rigid PVC pipe may crack. An insert fitting with a hose clamp or a compression fitting is used as connectors with poly-pipes. PolyChlorinated Biphenyls (PCBs) - a group of synthetic, toxic industrial chemical compounds once used in making paint and electrical transformers, which are chemically inert and not biodegradable. PCBs are frequently found in industrial wastes, finding their way into surface and ground waters. As a result of their persistence, they tend to accumulate in the environment. In terms of streams and rivers, PCBs are drawn to sediment, to which they attach and can remain virtually indefinitely, endangering the environment. Pop-up sprinkler head - a sprinkler head that retracts below ground level when it is not operating. Pores – (1) The voids between solid soil particles. (2) Channels or openings in a filtration medium which allow passage of fluid. Porosity – (1) A measure of the water-bearing capacity of subsurface rock. With respect to water movement, it is not just the total magnitude of porosity that is important, but the size of the voids and the extent to which they are interconnected, as the pores in a formation may be open, interconnected, or closed and isolated. For example, clay may have a very high porosity with respect to potential water content, but it constitutes a poor medium as an aquifer because the pores are usually too small. (2) The percentage of the soil volume that is occupied by pore spaces. (3) The ratio of pore volume to total volume of a filter medium expressed as a percentage. Positioner - Device that maintains the correct position of the throttling element in valve and ensures the adequate throttling or full shut-off of the valve. Potable water - Water which is fit for consumption by humans and animals;
- 270. 249 SPRINKLER IRRIGATION designated alsoas drinking water. Water may be naturally potable or it may need to be treated in order to be safe for drinking. Pounds per Square Inch (Psi) - A standard measure of water pressure in the imperial unit system. ppm - Parts per million. Precipitation - Rain, snow, hail, sleet, dew, and frost. Precipitation rate - The rate at which an irrigation system applies water. The common units of measure for precipitation rates are millimeters per hour (mm/h) or inches per hour (in the imperial unit system). Pre-filtration - Removal of coarse particles or large debris prior to a finer filtration process. Pressure at the head - The dynamic pressure as measured at the base of the emitter head. Pressure gauge - A device used to measure water pressure. The best pressure gauges are "liquid filled", however cheaper gauges, devoid of liquid, are good enough for irrigation system use. Pressure-loss - Loss in water pressure caused by friction of water against the inner walls of pipe or system components. Pressure rating - The allowed maximum internal pressure that can be continuously exerted in a pipe or container with a high degree of certainty that it will not fail. Pressure reducer - a device designed to reduce water pressure in supply system pipe or irrigation lines. Pressure Reducing Valve (PRV) - A self-operating valve used to reduce any excess pressure in a system. The valve opens if the internal pressure exceeds that holding the closing element onto the seat. Pressure Regulating Valve - A valve designed to automatically keep a preset downstream pressure in a hydraulic system. Pressure regulator - A device that regulates the available pressure to a preset maximum. Pressure relief valve - A valve that will be opened when its inlet pressure exceeds a preset value. Pressure Vacuum Breaker (PVB) – A device consisting of either one or two positive seating check valves and an internally force loaded disc float assembly, downstream of the check valves, installed as a unit between two tightly closing shut-off valves and fitted with properly located test cocks. The disc float assembly is force-loaded (generally by means of a spring) to a normally open position, and allows air to enter the piping system when the line pressure drops to 1 m (0.1 bar) or below. It introduces air into the system to prevent back siphonage. employs a spring loaded seat for positive opening to atmosphere. Since the disc float is force loaded, this device can be installed on the pressure side of a shut-off valve. However, it is designed to prevent back-siphonage only and is not effective against backflow due to backpressure. Pressure - The force over an area applied to an object in a direction perpendicular to
- 271. 250 SPRINKLER IRRIGATION its surface.Measured with a pressure gauge and expressed in bars, kPa or Pounds per Square Inch (PSI). It represents the amount of energy available to move water through pipes, valves, emitters or other components. Static pressure is the pressure measured when no water is flowing through a closed system. Dynamic pressure is the pressure measured when water is flowing through the system. Pre-treatment - The preliminary treatment in the processes of filtration and water reclamation (chemical or physical). Primary wastewater treatment - the first stage of the wastewater treatment process where mechanical means, such as filters and scrapers, are used to remove pollutants. Solid material in sewage also settles out in this process. Program - Information the user enters into controller’s memory that determines when the system will water. A program contains three pieces of information: what days to water, what time to start watering, and how much water will be applied. In time oriented programming, irrigation duration of each zone is determined instead of the water amoun to be applied. PSI - A pressure unit in the imperial unit system, Abbreviation for Pounds per Square Inch. Public supply - water withdrawn by public agencies and by private companies that is delivered to users. Pump (water-pump) - A device which converts mechanical force and motion into hydraulic fluid power. Pump curve - A graphic representation of the performance of a pump correlating the rate of flow against the total head. The efficiency of the pump can be obtained at selected points along the curve. Pump start circuit - The feature on an irrigation controller that allows a connection to be made through a relay, with the pump starter, so that the starter will be energized when a watering cycle begins. Pump start relay - An electronic device that uses a signal current from the irrigation controller to actuate a separate electrical circuit to energize the pump starter. PVC (PolyVinyl Chloride) pipe – (1) Rigid PVC pipe is more stiff than black poly- pipe, and requires the use of PVC solvents (glue) for connections. The pipe manufacturers also recommend the use of primer just prior to the application of the solvent to ensure a strong, watertight connection. Rigid PVC pipe can be used both as a mainline or as a lateral line provided it is buried in the soil. (2) Soft PVC pipes of small diameter are used in gardening and landscpe irrigation. They are sensitive to long-time exposure to sun-light. Quarter-turn - Category of valves (such as ball, plug, butterfly) which require just a 90 degree turn of the stem to change from the fully open to the fully closed position. Some larger valves may, for easier manual operation, be fitted with gearboxes, giving them the appearance of a multi-turn valve. Quick coupling - A permanently installed valve which allows direct access to the irrigation mainline for use of hoses. A quick coupling key is used to open the valve. Radius of throw - The distance from the emitter head to the furthest point of water application.
- 272. 251 SPRINKLER IRRIGATION Rain sensor- A device that automatically shuts off an irrigation system after a preset amount of precipitation falls. Rain switch - A simple on/off switch in an irrigation system that makes it easy to shut the system down during a rainstorm. Rainwater harvesting - the capture and use of runoff from rainfall. Raw water - Intake water prior to any treatment or use. Recharge - The addition of water to the groundwater supply by natural or artificial means. Reclaimed wastewater - Treated wastewater that can be used for beneficial purposes, such as irrigating certain crops. Recycled water - A type of reuse water usually run repeatedly through a closed system; sometimes used to describe reclaimed water. Reduced bore - Indicates that the internal diameter of the valve is smaller than the diameter of the pipe to which the valve is fitted. Reduced Pressure Backflow Preventer (RPBP, RP, RPA, RPZ) – A device consisting of two positive seating check valves, and an automatically operating pressure differential relief valve, internally located between the two check valves, installed as a unit between two tightly closing shut-off valves, and fitted with properly located test cocks. During normal operation, the pressure in the zone between the two check valves is maintained at a lower pressure than the supply pressure. If the zone pressure starts to approach the supply pressure, the differential pressure relief valve will automatically maintain a differential of not less than 1 m (0.1 bar) between the supply pressure and the zone between the two check valves by discharging water to the atmosphere. This device is effective against backflow caused by both backpressure and back siphonage and is used to protect potable water systems from substances immersed in the irrigation water which are hazardous to health. Reducer - A fitting used to change from certain pipe diameter to a smaller one. Reducer bushing - a small segment of pipe, used to connect two pipes of different sizes together. A standard reducer bushing has one male end (for the larger pipe) and one female connection (for the smaller pipe). Reference Evapo-Transpiration (ET0) - the evapo-transpiration of a broad expanse of adequately watered cool-season grass 10 - 15 cm in height. A standard measurement for determining maximum water allowances for plants so that regional differences in climate can be accommodated. Reference Evapo-Transpiration (ET0) of Low Crops - Represents the rate of evapo-transpiration from an extensive surface of cool-season grass cover of uniform height of 12 cm, actively growing, completely shading the ground, and not short of water. Reference Evapo-Transpiration (Etr) of Medium Height Crops - represents the rate of evapo-transpiration from an extensive surface of alfalfa or similar agricultural crop of uniform height of approximately 50 cm, actively growing, completely shading the ground, and not short of water. On the average ETr is 10% - 30% greater than ETo. Regulated Deficit Irrigation (RDI) - Irrigation management strategy where the plant
- 273. 252 SPRINKLER IRRIGATION root zoneis not filled with water to field capacity level and the plant water requirement is not fully met. Regulating valve - This valve type is used to regulate flows to provide a constant pressure output. Remote control - Device that can be used to activate electronic irrigation valves from a given distance away from the irrigation controller , actuated by an automatic controller of electric or hydraulic command. Reservoir - Any natural or artificial holding area used to store, regulate, or control water. Residual chlorine - The total concentration of chlorine remaining in water, sewage, or industrial wastes at the end of a specified contact period following chlorination; expressed in ppm units. Resistance block - type of soil moisture probe used to monitor soil moisture state for helping determine the timing of irrigation. Resistance (electrical) - The resistance to the flow of electrical current. It can be compared to friction-loss in an irrigation piping system. Resistance causes a drop in voltage along the length of a wire and is measured in ohms. Retrofit - Replacement of existing system components with new equipment that increase the efficiency of water use. Return-flow - (1) That part of a diverted flow that is not consumptively used and returned to its original source or another body of water. (2) (Irrigation) Drainage water from irrigated farmlands that re-enters the water system to be used further downstream. Reverse Osmosis (RO) - The process of removing salts from water, using a membrane. With reverse osmosis, the product water passes through a fine membrane that the salts are unable to pass through. The salt waste (brine) is removed and disposed. This process differs from electro-dialysis, where the salts are extracted from the feed-water by using a membrane with an electrical current to separate the ions. The positive ions go through one membrane, while the negative ions flow through a different membrane, leaving the end product of freshwater. This technique is used in desalination and water-reclamation practices. Riparian water rights - The rights of an owner whose land abuts water. Riparian users of a stream share the stream-flow among themselves, and the concept of priority of use (Prior Appropriation Doctrine) is not applicable. Riparian rights cannot be sold or transferred for use on non-riparian land. Riser - The pipe segment connecting an emitter or other irrigation device to the pipe or lateral that supplies the water to it. Root-zone - that volume of soil which plant roots readily penetrate and in which the predominant root activity occurs. Rotors – Emitters that distribute a solid stream of water and rotate slowly in a circular pattern. Runoff - (1) That part of the precipitation, snow melt, or irrigation water that appears in uncontrolled surface streams, rivers, drains or sewers. Runoff may be classified according to speed of appearance after rainfall or melting snow as direct runoff or
- 274. 253 SPRINKLER IRRIGATION base runoff,and according to source as surface runoff, storm interflow, or groundwater runoff. (2) The flow of water over the soil surface when rainfall (or irrigation) rate exceeds the infiltration rate of the soil. Runoff can detach and remove soil particles and thus cause erosion. (3) Also defined as the depth to which a drainage area would be covered if all of the runoff for a given period of time were uniformly distributed over it. Runtime - Length of time available to operate an irrigation system or an individual zone for a single irrigation event. Saline - the feature of containing dissolved or soluble salts beyond a specified level. Saline soils productivity is impaired by high soluble salt content. Saline water is that which would impair production if used to irrigate salt-sensitive crops without adequate leaching to prevent soil salinization. Saline water - Water that contains significant amounts of dissolved solids. parameters for saline water: Fresh water - Less than 1,000 parts per million (ppm) Slightly saline water - From 1,000 to 3,000 ppm Moderately saline water - From 3,000 to 10,000 ppm Highly saline water - Over 10,000 ppm Sampling valve - A valve which is fitted to an accessory or pipeline to allow small sample of a fluid to be withdrawn for further testing. Commonly, a standard gate or needle valve is used. The disadvantage is that inappropriate use may result in spillage. As an alternative, valves are available which ‘trap’ a small quantity of fluid in a chamber, and only this small amount of fluid is released when the valve is operated. Saturated flow - The movement of water in saturated soil (when all the pores are filled with water). Scale - Precipitate that forms on surfaces in contact with water as a result of chemical or physical change. Scheduling Coefficient (SC) - The SC is a measure of uniformity of water distribution in any specific irrigated area as it relates to the precipitation rate of the entire area. The SC is an indication of the additional system run-time necessary to compensate for dry areas. In a catchment test, the average precipitation rate for all catchments is divided by the lowest precipitation rate in a pre-dfined fraction of the area (mostly 5% - 10%) to establish the SC of the system. (A perfect SC of 1.0 states that all catchments in a zone fill to the same level.) Scheduling - The procedure of establishing and implementing the time and amount of irrigation water application. Screen (of filter) - Perforated cylindrical body made of metal or plastic wedge-wire or woven-wire elements housed in a plastic or steel body. Screen filtration - Filtration using a screen to remove solid particles out of water. Secondary wastewater treatment – The second step, following primary wastewater treatment, involving the biological process of reducing suspended, colloidal, and dissolved organic matter in effluent from primary treatment systems. Generally removes 80% - 95% of the Biochemical Oxygen Demand (BOD) and suspended matter. Secondary wastewater treatment may be accomplished by biological or
- 275. 254 SPRINKLER IRRIGATION chemical-physical methods.Activated sludge and trickling filters are two of the most common methods of secondary treatment. It is accomplished by bringing together waste, bacteria, and oxygen. This treatment removes floating and suspended solids and about 90% of the oxygen-demanding substances and solids. Disinfection is the final stage of the secondary treatment. Sediment - A material in suspension in water or recently deposited from suspension. In the plural the word is applied to all kinds of deposits from the waters of streams, lakes, or seas. Sediment load - Amount of sediment carried by running water. Sedimentation - Deposition of waterborne sediments due to a decrease in velocity and corresponding reduction in the size and amount of sediment which can be carried in the water. Sedimentation tanks – (1) Wastewater tanks in which floating wastes are skimmed off and settled solids are removed for disposal. (2) Tank for sedimentation of sand and other solids from the water by extremely slowing water movement by flowing through very wide cross-section. Seepage - (1) The slow movement of water through small cracks, pores, Interstices, etc., of a material into or out of a body of surface or subsurface water. (2) The loss of water by infiltration into the soil from a canal, ditches, laterals, watercourse, reservoir, storage facilities, other bodies of water, or from a field. Self-supplied water - water withdrawn from a surface or groundwater source by a user rather than being obtained from a public supply. Semi-arid climate - A climate characterized by 250 – 500 mm of annual precipitation. Sewage treatment plant - A facility designed to receive the wastewater from domestic and/or industrial sources and to remove materials that downgrade water quality and threaten public health and safety when used for irrigation or discharged into receiving streams or bodies of water. The substances removed are classified into five basic groups: [1] greases and fats; [2] solids from human waste and other sources; [3] dissolved pollutants from human waste and decomposition products; [4] dangerous microorganisms; [5] poisonous industrial residues. Most facilities employ a combination of mechanical removal steps and bacterial decomposition to achieve the desired results. Chlorine is often added to the water to reduce the danger of spreading diseases by the release of pathogenic bacteria. Sewer - A system of underground pipes that collect and deliver wastewater to treatment facilities or streams. Simple water budget - A water budget that is the product of reference evapo- transpiration, irrigated area, and a conversion factor, relating to the specific requirements of the crop. Sludge - The residual semi-solid material left from the water reclamation process. Snaking - Laying of loosened laterals to allow temperature induced contraction and
- 276. 255 SPRINKLER IRRIGATION elongation beforethe final set-up of the system. Softening - The removal of calcium and magnesium ions from water. Soil amendment - The addition of organic and inorganic materials to soil to improve its texture, nutrient load, moisture-holding capacity, and infiltration rate. Soil auger - A metallic device used for drilling into the soil and removing soil samples for analysis. Soil conservation - Protection of soil against physical damage and loss by erosion and chemical deterioration by the implementation of management and land use practices that safeguard the soil against the natural and human induced detrimental factors. Soil moisture deficit - the amount of water required to replenish the soil moisture to field capacity level in the plant root zone at the time of irrigation, expressed as a depth of water in mm. Soil moisture replacement - The amount of water applied to replace a portion of all of the soil moisture deficit, expressed as a depth of water in mm. Soil moisture sensor - A device positioned in the ground at the plant root zone depth to measure the water state in the soil. Soil moisture sensors are used to control irrigation and indicate whether watering is required or not. Soil moisture - Water stored in soil. Soil probe - A soil-coring tool that allows an intact soil core to be removed from the soil profile for examination. Soil profile - A vertical cross-section of the relevant depth of the soil at a specific site, exposed by digging a soil pit. Soil texture - The classification of soil according to the distribution of particle sizes, designated as its percentage of sand, silt, and clay. Solenoid valve - An automatic valve actuated by electrical signals operates under low voltage (24v AC) which may be remotely actuated and controlled via a cable or wireless from the central controller. Typically, valves of the needle and globe types are operated by an electrical solenoid. They are often deployed as pilot valves, i.e., fitted to actuators which in turn control larger valves. Solute - A substance that is dissolved in a fluid, thus forming a solution. Solution - A mixture of a solvent and a solute. Solvent - A fluid that dissolves other substances thus forms a solution. Water dissolves more substances than any other fluid, and is known as the "universal solvent". Solvent welding - The act of chemically fusing pipes and fittings together using solvent and cement. Specific conductance - A measure of the ability of water to conduct an electrical current as measured using a 1-cm cell and expressed in units of electrical conductance, i.e., Siemens or deciSimens (dS) per centimeter at 250 C. Specific conductance can be used for approximating the total dissolved solids content of water by testing its capacity to carry an electrical current. In water quality detection, specific conductance is used in ground water monitoring as an indication of the
- 277. 256 SPRINKLER IRRIGATION presence ofions of chemical substances that may have been released by a leaking landfill, other waste storage or disposal facility. A higher specific conductance in water drawn from down-gradient wells when compared to up-gradient wells indicates possible contamination from the facility. Spray heads Emitters that discharge a fan-type spray of small droplets of water. These heads generally have a wetting radius of 5 m and less. Sprinkler distribution pattern - Two-dimensional water depth-distance relationship measured for a single or multiple sprinklers. Sprinklers - Devices that distribute water through the air, over a given area for irrigation. Sprinkler irrigation - An irrigation method where water is shot from high, medium or low pressure emitters through the air, onto crops. In that technology, some water is lost to evaporation. Static water pressure - water pressure as measured when the water is not moving. When measuring static water pressure all the water outlets on the pipe must be closed. Station - A circuit on an irrigation controller that can be programmed with a run-time separate from other circuits and provides power to one or more remote control valves. Stream - A general term for a body of flowing water; natural water course containing water at least part of the year. In hydrology, it is generally applied to the water flowing in a natural channel as distinct from a manmade canal. Stream rotors - Emitter heads that deliver rotating streams of water in partial or full circles at relative low precipitation rates. Stream-flow - The water discharge that occurs in a natural channel. A more general term than runoff, stream-flow may be applied to discharge whether or not it is affected by diversion or regulation. Subsidence - A dropping of the land surface as a result of ground water being pumped. Cracks and fissures can appear in the land. Subsidence is virtually an irreversible process. Substrate - A mineral or organic material that provides anchoring medium and reservoir of water and nutrients for the plants. Suction-scanning (also known as focused back-flush) - Suction force that is created by reversing flow through a small section of the screen element into a nozzle at the tip of a rotating scanning element in filters. Supplemental irrigation - The application of water to a crop to supplement natural precipitation. Surface irrigation - The application of water to land by surface flow driven by gravity. Surface tension - The force acting on molecules at the surface of a liquid resulting from the attraction of the liquid molecules to each other. Thus, a barrier is created between the air and the liquid. Surface water - All water naturally opened to the atmosphere (rivers, lakes,
- 278. 257 SPRINKLER IRRIGATION reservoirs, ponds,streams, impoundments, seas, estuaries, etc.). Surface water supply - Water supplied from a stream, lake, or reservoir. Surge - An energy wave in pipelines caused by abrupt opening or closing of valves. Surge irrigation - A surface irrigation technique wherein flow is applied to furrows (or less commonly, borders) intermittently during a single irrigation set. Suspended-sediment - Very fine soil particles that remain in suspension in water for a considerable period of time without contact with the bottom of canals, pipes, tanks and accessories. Such material remains in suspension due to the upward components of turbulence and currents and/or by suspension. Suspended-sediment concentration - The ratio of the mass of dry sediment in a water-sediment mixture to the mass of the water sediment mixture. Typically expressed in milligrams of dry sediment per liter of water-sediment mixture. Suspended solids - solids that are not in true solution and that can be removed by filtration or sedimentation. Such suspended solids usually contribute directly to turbidity. Defined in waste management, these are small particles of solid pollutants that resist separation by conventional methods. Swing-check - A non-return valve that employs a hinged disk as the closing element. Swing-joint - A combination of threaded pipe and fittings used between the pipe and sprinkler that allows movement to be taken up in the threads rather than as a sheer force on the pipe. Can also be used to raise or lower sprinklers to final height without plumbing changes. Tail-water - Applied irrigation water that runs off the lower end of a field. Tail-water is measured as the average depth of runoff water, expressed in mm. Tank-valve - A valve arranged for fitting at the bottom of a tank. Tensiometer - Instrument consisting of a porous cup filled with water and connected to a manometer or vacuum gage; used for measuring the soil-water matric potential that indicates the soil moisture content. Tertiary treatment - Advanced cleaning treatment of wastewater that goes beyond the secondary or biological stage, removing nutrients such as phosphorus, nitrogen, and most BOD and suspended solids. Selected biological, physical, and chemical separation processes are employed to remove organic and inorganic substances that resist conventional treatment practices. the additional treatment of effluent is aimed to obtain a very high quality of effluent. The complete wastewater treatment process typically involves a three-phase process: (1) First, in the primary wastewater treatment process, which incorporates physical aspects, untreated water is passed through a series of screens to remove solid wastes; (2) Second, in the secondary wastewater treatment process, typically involving biological and chemical processes, screened wastewater is then passed a series of holding and aeration tanks and ponds; and (3) Third, the tertiary wastewater treatment process consists of flocculation basins,
- 279. 258 SPRINKLER IRRIGATION clarifiers, filters,and chlorine basins or ozone or ultraviolet radiation processes. Throttle - A restriction of the cross-section of water passage in valves, pipes and other water passageways. Total Dissolved Solids (TDS) - A measure (in mg/l units) of the mineral salts that will be deposited after the water had completely evaporated. Total Dynamic Head (TDH) - The sum of operation head, friction head and elevation head. The total energy that a pump must incorporate in the water to guarantee optimal function of the irrigation system. Total Suspended Solids (TSS) - A measure of all suspended solids in a liquid, not including the dissolved salts, expressed in mg/l. Trajectory - The angle, relating to soil surface, of the water spattered out into the air from the emitter's nozzle. Transitional (semi-turbulent) flow - A mix of laminar and turbulent flow, with turbulence in the center of the pipe, and laminar flow near the walls. Each of these flows behaves differently in terms of their frictional energy loss while flowing. Transmissibility (ground water) - The capacity of a rock to transmit water under pressure. The coefficient of transmissibility is the rate of flow of water, at the prevailing water temperature, in liters per day, through a vertical strip of the aquifer one foot wide, extending the full saturated height of the aquifer under a hydraulic gradient of 100%. A hydraulic gradient of 100% means a one m drop in head in one m of flow distance. Transpiration - The transfer of water vapor from plants to air. The water that is absorbed by plants, usually through the roots, is evaporated into the atmosphere from the plant surface, mainly from the leaf stomata. Treatment plant - A structure built to treat wastewater before discharging it into the environment. Turbidity - The amount of solid particles that are suspended in water and that cause light rays shining through the water to scatter. Thus, turbidity makes the water cloudy or even opaque in extreme cases. The measurement of turbidity is a key test of water quality and it is measured as the amount of Light transmission through a water sample. The turbidity is expressed in nephelometric turbidity units (NTU). Turbulent flow - Flow pattern in which vortices, eddies and wakes make the flow unpredictable. The flow regime is characterized by random direction changes as well as rapid variation of pressure and velocity in space and time. Turbulent flow happens generally at high flow velocities and causes higher friction head losses than the same flow-rate in laminar flow. UPVC pipe - Unplasticized Polyvinyl Chloride pipe. Has better endurance and flexibility than ordinary PVC pipes. Under-irrigation - The difference between the water stored in a plant root zone during irrigation and the amount needed to refill the root zone to field capacity. Uniformity - The evenness of precipitation over a given area. Union - A pipe fitting used to connect two segments of pipe in such a way that neither has to be rotated.
- 280. 259 SPRINKLER IRRIGATION Unsaturated zone- The layer immediately below the soil surface where the pores contain both water and air, but are not totally saturated with water. These zones differ from an aquifer, where the pores are saturated with water. Valve – (In irrigation and water supply) A device used to control the flow of water. Valves used in pressurized systems include: Angle Valves, Ball valves, Drain Valves, Gate Valves, Globe valves, Hydraulic Valves, isolation valves, Pressure Regulating Valves, Pressure Sustaining Valves, Air Release Valves, Vacuum Breaking Valves, Automatic Control Valves. Isolation valves are used to shut-off water for repairs. Control valves turn on and off the water to individual zones of sprinklers or drip emitters. Check valves allow the water to flow in only one direction. Master valves are located at the water source and turn on and off the water for the entire irrigation system when not in use. Valve zone - An area where irrigation is all controlled by a single control valve. Each valve zone must be within only one hydro-zone. Vapor pressure - The pressure at which water evaporates at a given temperature; the temperature at which the vapor pressure is equal to the atmospheric pressure is called the boiling point. Velocity – (Of water) The speed at which water travels through a pipe or other conduit. The maximum recommended water velocity is 1.5 m/s in supply networks and 2.0 – 2.5 m/s in irrigation systems. Viscosity - The resistance of a fluid to flow, caused by internal friction between the fluid molecules and by intermolecular forces. Voltage - Amount of electrical potential required to force one amper of current flow in a circuit against one ohm of resistance. Wafer design - The construction of wafer design valves allows them to be ‘sandwiched’ between flanged sections of pipeline. The benefit is lower bolting requirements. Typically used with certain butterfly and check valves. Wastewater - Spent or used water from individual homes, a community, a farm, or an industry plant that contains dissolved or suspended matter... Wastewater treatment plant - A facility with an engineered system designed to remove pollutants, such as organic matter, poisonous chemicals, phosphorus and nitrogen, from municipal and industrial wastewater for irrigation or discharge into surface waters. Wastewater-treatment return flow - water returned to the environment by wastewater-treatment facilities. Water audit - An on-site survey and assessment of water-using hardware, fixtures, equipment, irrigation systems, and management practices to determine the efficiency of water use and to develop recommendations for improving water use efficiency. Water budget - The amount of water required to maintain crop profitable; a method of establishing water efficiency standards by prescribing limits on water applications. Water conservation - Activities designed to reduce the demand for water, improve efficiency in use, and reduce losses and waste of water. Water cycle - the circuit of water movement from the oceans to the atmosphere and to the Earth and return to the atmosphere through various stages or processes such
- 281. 260 SPRINKLER IRRIGATION as precipitation,interception, runoff, infiltration, percolation, storage, evaporation, and transportation. Water delivery system - Reservoirs, canals, ditches, pipes, pumps, and other facilities to move water. Water hammer - The surging of pressure which occurs when a valve is suddenly closed. In extreme conditions, this surging will cause the pipes to vibrate or create a pounding noise. Water hammer is most commonly caused by fast closing valves and/or high velocity water flow. Water harvesting - The capture and use of runoff from rainfall. Water meter - A device used to measure the flow of water. Water quality - A term used to describe the chemical, physical, and biological characteristics of water, usually in respect to its suitability for a particular purpose. Water reclamation - The treatment of wastewater to make it reusable for non- potable purposes. Water recycling: the treatment of urban wastewater to make it reusable for a specific beneficial purpose. Water reuse - Deliberate use of reclaimed water or wastewater in compliance with applicable rules for a beneficial purpose (agricultural irrigation, landscape irrigation, aesthetic uses, ground water recharge, industrial uses, and fire protection). Water right - A legally protected claim to take possession of water occurring in a natural waterway and to divert that water for beneficial use. Water table - In an unconfined aquifer, the top of the saturated zone; the level at which a well penetrates the top of an unconfined aquifer. Water Use Efficiency (WUE) - The amount of dry vegetal matter produced per unit of applied water. Expressed as g/m3 (grams of dry matter per m3 of applied water). Watering window - The span of hours and days of the week that water is available for irrigation. Watershed - The area from which all precipitation and runoff drain into a single water source or conduit. Watt-hour (Wh) - An electrical energy unit of measure equal to one watt of power supplied to, or taken from, an electrical circuit steadily for one hour. Weather station - A facility where meteorological data are measured and gathered. Well (water) - An artificial excavation put down for the purpose of withdrawing water from the underground aquifers. A bored, drilled, or driven shaft or a dug hole whose depth is greater than the largest surface dimension and whose purpose is to reach underground water supplies or oil, or to store or bury fluids below ground. Wetlands - lands including swamps, marshes, bogs, and similar areas such as wet meadows, river overflows, mud flats, and natural ponds. That area is characterized by periodic inundation or saturation, hydric soils, and vegetation adapted for life in saturated soil conditions. Wire - In an automatic irrigation system, low voltage direct burial wire is used to connect the automatic control valves to the controller. The most frequently used wire for commercial applications is single strand, heavy gauge direct burial copper wire.
- 282. 261 SPRINKLER IRRIGATION (The largerthe gauge number, the thinner the wire.) The most frequently used wire for landscpe sprinkler systems is multi-strand. Color-coded, multi-strand wire has several coated wires together in one protective jacket. Xeriscaping - A method of landscaping that uses plants that are well adapted to arid and semi-arid climate and are drought-resistant. Xeriscaping is becoming more popular as a way of saving water. Zone: A zone is the area to be watered from one control head valve.
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