Chapter 4.pdf

4.Water application Techniques
Ceng5082
Mengistu .Z (MSc in Hydraulic Engineering )
Lecturer @ Hydraulic and Water Resources Engineering department
Mizan Tepi university
Email: mengistu.zantet@gmail.com
mengistuzantet@mtu.edu.et
P.O.Box: 260
Tepi, Ethiopia
25-May-22 1
lecturer@ Hydraulic and water
resources Engineering Department

4. General aspects of Water Application Techniques
4.1 Land Grading, Survey and Design
4.2 Border
4.3 Furrow
4.4 Check-Basin
4.5 Drip
4.6 Sprinkler mengistuzantet@mtu.edu.et
resources Engineering Department 2

4.1 Land preparation and field layout
 Land grading is reshaping of the field surface
to a planned grade
Land levelling operations may be grouped into
three phases:
1) Rough grading
2) Land levelling
3) Land smoothing
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Criteria for land levelling
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Land levelling is influenced by
The characteristics of the soil profile,
Prevailing land slope
Rainfall characteristics
Cropping pattern
Methods of irrigation

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 Determining the centroid of the filed:
The distance of the centroid from the reference line is then
obtained by dividing the sum of the products by the total number
of stakes
 Determining the average elevation of the field:
This is obtained by adding the elevations of all grid points in the
field and dividing the sum by the number of points.
 Compute the slope of the plane of best fit
 The slope of any line in the x or y direction on the plane which
fits the natural ground surface, can be determined by the least

25-May-22
Line Distance No Stakes Product
A 12.5 9 112.5
B 37.5 9 337.5
C 62.5 9 562.5
D 87.5 9 787.5
E 112.5 9 1012.5
F 137.5 7 962.5
G 162.5 6 975.0
Total 58 4750.0

4.2 IRRIGATION METHODS
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1.Surface Irrigation:
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surface irrigation is the oldest and most common
method of irrigation, it does not result in high levels of
performance.
This is mainly because of uncertain infiltration rates
which are affected by year-to-year changes
in the cropping pattern, cultivation practices, climatic
factors, and many other factor
Just flooding water. About 90% of the irrigated areas
in the world are by this method.

Surface Irrigation Classified
1) Border Strip Irrigation Method
Border strip irrigation (or simply ‘border irrigation’) is a controlled surface flooding
method of applying irrigation water. In this method, the farm is divided into a number of
strips which can be 3-20 meters wide and 100-400 meters long.
2) Basin Irrigation Method
This method is frequently used to irrigate orchards. Generally, one basin is made for
one tree. However, where conditions are favorable, two or more trees can be included in
one
basin.
3) Furrows Irrigation are small channels having a continuous and almost uniform slope
in the direction of irrigation
Furrows are used to irrigate crops planted in rows.
1)
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Advantages of surface irrigation
It is more acceptable to agriculturalists that easier to
apply the depth of required to fill the root zone.
It can be developed at the farm level with minimal
capita investment.
Energy requirements come from gravity.
are less affected by climatic and water quality
characteristics.
Generally the gravity flow is system is highly flexible,
relatively easily-managed method of irrigation.
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Disadvantages of surface irrigation
 It is very difficult to define the primary
design variables, discharge and time of
application, due to the highly spatial and
temporal variability of the soil.
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Surface irrigation event four distinct hydraulic phases can be
discerned:
 Advance phase: the time interval between the start of irrigation and arrival
of the advancing (wetting) front at the lower end of the field.
Ponding (wetting storage or continuing) phase: the irrigation time
extending between the end of advance and inflow cutoff. The term “Wetting”
phase is usually used for furrow and border where tail water runoff can occur,
whereas ponding is the preferred term for basin irrigation (no tail water runoff)
Depletion (vertical recession) phase: the time interval between supply cut-
off and the time that water dries up at the inlet boundary.
Recession (horizontal recession) phase: the time required for the water to
recede from all points in the channel, starting from the end of the depletion
phase. The time difference at each measuring station between the clock time or
cumulative time for advance and recession is the opportunity time, T, infiltration
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Surface Irrigation Methods
1) Wild flooding
2) Basin irrigation
3) Border irrigation
4) Furrow irrigation
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Criteria for the selection of surface irrigation methods
Natural circumstances (slope, soil type)
Type of crop,
Required depth of application,
Level of technology,
Previous experiences with irrigation,
 Required labour input.
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Design of Surface Irrigation Systems
 The design of a surface irrigation system first involves
assessing the general topographic conditions, soils,
crops, farming practices anticipated and farm
operators desires and finance for the field or farm in
question
 The first priorities in agriculture today is the
development of irrigation design that are more
efficient in the use of both water and energy resources
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Surface irrigation Design inputs (System Parameters and
System Variables)
System Parameters
1.Required amount of application (Zr)
2. Maximum allowable flow velocity (Vmax)
3. Manning’s roughness coefficient (n).
4. Channel bed slope (So).
5. Infiltration parameter (I).
6. Channel geometry
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System Variables
1. Channel length (l).
2. Unit inlet flow rate (Qo).
3. Cutoff time (tco)
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Surface irrigation system performance
The best surface irrigation scenario (event) is one that can apply
the right amount of water over the entire subject area and
without loss
In real life systems uneven and excess application of irrigation
water are the “twins facts of life’ that engineers and irrigators
ought to live with.
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The performance of a surface irrigation event can be
evaluated from three distinct
(1) Excess application of irrigation water
(2) Adequacy of irrigation,
(3) Uniform (even) application of irrigated water over the
entire subject area
Distribution uniformity (DU) and Christiansen`s
uniformity coefficient (UC) are the most commonly used
indices in surface irrigation application
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Irrigation uniformity
 Uniformity of infiltration under surface irrigation
depends on the spatial and temporal variability of
surface and sub-surface hydraulic characteristics such
as field slope, furrow geometry, surface roughness,
field length, flow rate and soil pore size distribution.
 Two parameters are used to evaluate distribution
uniformity
1) distribution uniformity coefficient DU
2) Christansen `s uniformity coefficient, (UCC),
25-May-22

Distribution uniformity coefficient DU
 is defined as the ratio of the minimum infiltrated amount
expressed as percentage of the average infiltrated amount over
the subject area.
 A general expression for DU is:DU=
𝑍𝑚𝑖𝑛
𝑍𝑎𝑣
*100
 Where Zmin = minimum infiltrated amount over the length
of the run of the subject area (m3. m-1).
 Zav = average infiltrated amount over the length of
the run of the subject area (m3. m-1) and Zav is expressed as ,
Zav=
𝑍𝑑𝑥
𝑙𝑜𝑣
0
𝐿

Christensen `s uniformity coefficient, (UCC),
defined as the ratio of the difference between
the average amount applied and the average
deviation from the average amount applied to
the average amount applied.

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Hydraulic Design of
Surface Irrigation
Systems
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Design of furrow irrigation System
a) Shape and Spacing of Furrows:
Heights of ridges vary between 15 cm and 40 cm
and the distance between the ridges should be
based on the optimum crop spacing modified, if
necessary to obtain adequate lateral
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b) Selection of the Advance or Initial Furrow Stream
The empirical relation developed by USDA-SCS for the
maximum non-erosive stream size is
Qmax =
𝐶
𝑆
………………………………………………………………..(1)
Where S = ground slope down the furrow in %
C = empirical constant (= 0.6
𝐿
𝑆
)
This relationship doesn’t account for soil type and
26

c) Cut-back Stream: This is the stream size to
which the initial stream is reduced sometime after
it has reached the lower end of the field.
•This is to reduce soil erosion.
One or two cutbacks can be carried out and
removing some siphons or reducing the size at
the head of the furrow achieves this.
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d) Field Slope: To reduce costs of land grading,
longitudinal and cross slopes should be adapted
to the natural topography.
•Small cross slopes can be tolerated.
• To reduce erosion problems during rainfall,
furrows (which channel the runoff) should have a
limited slope (see Table 3.1).
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Field Slope (Source: Withers & Vipond (1974)
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Soil Type Maximum slopes*
Sand 0.25
Sandy loam 0.40
Fine sandy loam 0.50
Clay 2.50
Loam 6.25
*A minimum slope of about 0.05 % is required to ensure
surface drainage.

e) Furrow Length: Very long lengths lead to a
lot of deep percolation involving over-irrigation
at the upper end of the furrow and under-
irrigation at the lower end.
•Typical values are given in Table 3.2, but actual
furrow lengths should be got from field tests.
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Design Parameters of Border Irrigation System
A) Strip width: Cross slopes must be eliminated by leveling.
•Since there are no furrows to restrict lateral movement, any cross slope will
make water move down one side leading to poor application efficiency and
possibly erosion.
•The stream size available should also be considered in choosing a strip width.
•The size should be enough to allow complete lateral spreading throughout the
length of the strip.
•The width of the strip for a given water supply is a function of the length (Table
3.5).
•The strip width should be at least bigger than the size of vehicle tract for
construction where applicable.
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b) Strip Slope: Longitudinal slopes should be almost
same as for the furrow irrigation.
c) Construction of Levees: Levees should be big
enough to withstand erosion, and of sufficient height
to contain the irrigation stream.
d) Selection of the Advance Stream: The maximum
advance stream used should be non-erosive and
therefore depends on the protection afforded by the
crop cover. Clay soils are less susceptible to erosion
but suffer surface panning at high water velocities.
Table 3.4 gives the maximum flows recommendable
for bare soils.
e) The Length of the Strip: Typical lengths and widths
for various flows are given in Table 3.5. The ideal
lengths can be obtained by field tests.
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25-May-22

Basin Irrigation System
 In basin irrigation, water is flooded in wider areas. It is
ideal for irrigating rice.
 The area is normally flat.
 In basin irrigation, a very high stream size is introduced
into the basin so that rapid movement of water is
obtained.
 Water does not infiltrate a lot initially.
 At the end, a bond is put and water can pond the field.
 The opportunity time difference between the upward
25-May-22

Size of Basins
The size of basin is related to stream size and soil type(See Table 3.6 below).
Table 3.6: Suggested basin areas for different soil types and rates of water flow
Flow rate Soil Type
Sand Sandy loam Clay loam Clay
l/s m3 /hr .................Hectares................................
30 108 0.02 0.06 0.12 0.20
60 216 0.04 0.12 0.24 0.40
90 324 0.06 0.18 0.36 0.60
120 432 0.08 0.24 0.48 0.80
150 540 0.10 0.30 0.60 1.00
180 648 0.12 0.36 0.72 1.20
210 756 0.14 0.42 0.84 1.40
240 864 0.16 0.48 0.96 1.60
300 1080 0.20 0.60 1.20 2.00
...........................................................................................
Note: The size of basin for clays is 10 times that of sand as the infiltration rate for clay
is low leading to higher irrigation time. The size of basin also increases as the flow rate
increases. The table is only a guide and practical values from an area should be relied
upon. There is the need for field evaluation.
37

2.Sub-Surface Irrigation
25-May-22
Subsurface irrigation (or simply sub irrigation) is
the practice of applying water to soils directly
under the surface.
Moisture reaches the plant roots through
capillary action
Flooding water underground and allowing it to
come up by capillarity to crop roots.

The conditions which favors sub irrigation are
25-May-22
 Impervious subsoil at a depth of 2 meters or
more,
 very permeable subsoil,
 A permeable loam or sandy loam surface soil,
 Uniform topographic conditions, and
 Moderate ground slopes


3.Pressurized irrigation
25-May-22
Water moves through the pipes under pressure,
it is not exposed to the atmosphere as in the
open channels
Energy is required in order to develop enough
head to overcome frictional resistances in the
pipe and pump sections so that adequate
amount of supply can reach the point of
interest.

Pressurized irrigation Classified
25-May-22
A) Sprinkler Irrigation:
is the method of applying water to the soil surface in
the form of a spray which is some what similar to rain.
 In this method, water is sprayed into the air and
allowed to fall on the soil surface in a uniform pattern
at a rate less than the infiltration rate of the soil
Applying water under pressure. About 5 % of the
irrigated areas are by this method.

The following conditions are favorable for sprinkler irrigation
25-May-22
Very previous soils which do not permit good
distribution of water by surface methods,
Lands which have steep slopes and easily erodible
soils,
Irrigation channels which are too small to distribute
water efficiently by surface irrigation, and
Lands with shallow soils and undulating lands which
prevent proper levelling required for surface methods of

Advantages of sprinkler Irrigation
Used on all types of soils on lands of different
topography and slopes, and for many crops
Saving of money as well as water
Popular in the developed countries and is gaining
popularity in the developing countries too
It has higher water application/use efficiency, less
labor requirements, adaptability to hilly terrain, and
ability to apply fertilizers in solution
25-May-22 43

Limitation of sprinkler Irrigation
 Wind distorts sprinkler pattern and causes uneven
distribution of water
 Ripened soft fruits may be affected by spraying water.
 Water must be clean and free of sand, debris and large
amount of dissolved salts.
 High initial investment as compared to surface irrigation.
 High power requirements
 Fine textured soils with slow infiltration rate can not be
irrigated efficiently in hot windy areas
25-May-22

Design of Sprinkler Irrigation System
Design Steps
 Determine Irrigation Water Requirements and
Irrigation Schedule
 Determine Type and Spacing of Sprinklers
 Prepare Layout of Mainline, Submains and Laterals
 Design Pipework and select Valves and Fittings
 Determine Pumping Requirements.
25-May-22

Choice of Sprinkler System
Consider:
Application rate or precipitation rate
Uniformity of Application: Use UC
Drop Size Distribution and
Cost
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Sprinkler Application Rate
Must be Less than Intake Rates
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Effects of Wind in sprinkler irrigation
 Reduce the spacing between Sprinklers: See table 6 in
Text.
 Aligns Sprinkler Laterals across prevailing wind
directions
 Build Extra Capacity
 Select Rotary Sprinklers with a low trajectory angle.
25-May-22

System Layout
 Layout is determined by the Physical Features of the
Site e.g. Field Shape and Size, Obstacles, and
topography and the type of Equipment chosen.
 Where there are several possibilities of preparing the
layout, a cost criteria can be applied to the
alternatives.
 Laterals should be as long as site dimensions,
pressure and pipe diameter restrictions will allow.
 Laterals of 75 mm to 100 mm diameter can easily be
49

Design of Laterals
 Laterals supply water to the Sprinklers
 Pipe Sizes are chosen to minimize the pressure
variations along the Lateral, due to Friction and
Elevation Changes.
 Select a Pipe Size which limits the total pressure
change to 20% of the design operating pressure of the
Sprinkler.
 This limits overall variations in Sprinkler Discharge to
50

Lateral Discharge
The Discharge (QL) in a Lateral is defined as
the flow at the head of the lateral where water
is taken from the mainline or submain.
Thus: QL = N. qL Where N is the number of
sprinklers on the lateral and qL is the Sprinkler
discharge (m3/h)
25-May-22

Selecting Lateral Pipe Sizes
 Friction Loss in a Lateral is less than that in a Pipeline
where all the flow passes through the entire pipe
Length because flow changes at every sprinkler along
the Line.
 First Compute the Friction Loss in the Pipe assuming
no Sprinklers using a Friction Formula or Charts and
then:Apply a Factor, F based on the number of
Sprinklers on the Lateral (See Text for F Values)
25-May-22

Changes in Ground Elevation
Allowance must be made for Pressure changes
along the Lateral when it is uphill, downhill or
over undulating land.
 If Pe1 is the Pressure Difference Due to
Elevation changes:
25-May-22
downhill
laid
laterals
for
F
P
P
P
uphill
laid
laterals
for
F
P
P
P
eL
a
f
eL
a
f




2
.
0
2
.
0

Pressure at Head of Lateral
 The Pressure requirements (PL)where the Lateral joins the
Mainline or Submain are determined as follows:
 PL = Pa + 0.75 Pf + Pr For laterals laid on Flat land
 PL = Pa + 0.75 (Pf Pe) + Pr For Laterals on
gradient.
 The factor 0.75 is to provide for average operating
pressure (Pa) at the centre of the Lateral rather than at
the distal end. Pr is the height of the riser.
25-May-22 54

Diagram of Pressure at Head of Lateral
55

Selecting Pipe Sizes of Submains and Mainlines
As a general rule, for pumped systems, the
Maximum Pressure Loss in both Mainlines and
Submains should not exceed 30% of the total
pumping head required.
This is reasonable starting point for the
preliminary design.
Allowance should be made for pressure
changes in the mainline and submain when
they are uphill, downhill or undulating.
25-May-22

Pumping Requirements
Maximum Discharge (Qp) = qs N Where:
qs is the Sprinkler Discharge and
N is the total number of Sprinklers operating at
one time during irrigation cycle.
The Maximum Pressure to operate the system
(Total Dynamic Head, Pp) is given as shown in
Example.
25-May-22

2.Drip or Trickle Irrigation
Trickle irrigation (also known as drip irrigation) system
comprises main line (37.5 mm to 70 mm diameter pipe),
submains (25 mm to 37.5 mm diameter pipe), laterals (6 mm to 8
mm diameter pipe), valves (to control the flow), drippers or
emitters (to supply water to the plants),pressure gauges, water
meters, filters (to remove all debris, sand and clay to reduce
clogging of the emitters), pumps, fertilizer tanks, vacuum
breakers, and pressure regulators
25-May-22

Drip irrigation has several advantages
It saves water, enhances plant growth and crop
yield,
saves labor and energy,
controls weed growth,
causes no erosion of soil,
does not require land preparation, and
also improves fertilizer application efficiency
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Disadvantages of Drip irrigation
25-May-22
it requires high skill in design, installation,
and subsequent operation.

Design of Trickle r Irrigation System
25-May-22
 The diameter of the lateral should be selected so
that the difference in discharge between emitters
operating simultaneously will not exceed 10 %.
 This allowable variation is same as for sprinkler
irrigation laterals already discussed.
 To stay within this 10 % variation in flow, the head
difference between emitters should not exceed 10
to 15 % of the average operating head for long-

Design of Trickle Irrigation System
The maximum difference in pressure is the
head loss between the control point at the
inlet and the pressure at the emitter farthest
from the inlet.
The inlet is usually at the manifold where the
pressure is regulated.
 The manifold is a line to which the trickle
laterals are connected.
25-May-22 62

Design of Trickle r Irrigation System
 For minimum cost, on a level area 55 % of the allowable
head loss should be allocated to the lateral and 45 % to
the manifold.
 The Friction Loss for Mains and Sub-mains can be
computed from Darcy-Weisbach equation for smooth
pipes in trickle systems when combined with the Blasius
equation for friction factor.
 The equation is: Hf = K L Q 1.75 D – 4.75
Where: Hf is the friction loss in m;
 K is constant = 7.89 x 105 for S.I. units for water at 20 °
C; L is the pipe length in m;
 Q is the total pipe flow in l/s; and D is the internal
diameter of pipe in mm.
25-May-22 63

Design of Trickle Irrigation System
•As with sprinkler design, F should be used to
compute head loss for laterals and manifolds
with multiple outlets, by multiplying a suitable F
factor
•(See Table 8 of Sprinkler Design section) by
head loss.
•F values shown below can also be used.
25-May-22 64

25-May-22

THE END
25-May-22

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