2. CHAPTER FOUR
IRRIGATION METHODS
4.1 Surface Irrigation Methods
The term 'surface irrigation' refers to a broad class of irrigation methods in which
water is distributed over the field by overland flow(through open channels).
A flow is introduced at one edge of the field and covers the field gradually.
Gravity provides the major driving force to spread water over the irrigated field.
In a surface irrigation event four distinct hydraulic phases can be discerned:
1) Advance phase:
2) Ponding (wetting storage or continuing) phase
3) Depletion (vertical recession) phase
4) Recession (horizontal recession) phase
3. IRRIGATION METHODS
Surface Irrigation: Just flooding water. About 90% of the irrigated areas in the world are by this
method.
Sprinkler Irrigation: Applying water under pressure. About 5 % of the irrigated areas are by this
method.
Drip or Trickle Irrigation: Applying water slowly to the soil ideally at the same rate with crop
consumption.
The following conditions influence choice of irrigation method:
Topography- surface irrigations require smaller slopes and little land preparation than
pressurized systems
Economy- surface irrigations low initial investment but higher operation labor cost. The inverse is
true for pressurized systems.
Water quantity and quality- surface irrigations require large quantity of water with a fair quality
while pressurized systems require small quantity of water with good quality.
Crop economic value- pressurized systems are best suited for high economic value crops.
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4. Surface Irrigation
Features of surface Irrigation methods
Water is applied to the field in either the controlled or uncontrolled manner.
◦ Controlled: Water is applied from the head ditch and guided by corrugations, furrows,
borders, or ridges.
◦ Uncontrolled: Wild flooding.
Surface irrigation is entirely practiced where water is abundant.
Problems of surface irrigations
Uneven water distribution (not uniform): due to contact time difference
between the head and tail end of the field.
Percolation loss: due to large contact time or greater infiltration near the head of
the field.
Runoff loss: due to continuous supply of water after the water has reached the
tail end of the field.
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5. Types of surface irrigations
Wild Flooding
These are important for situations where the value of the crop is very small( the field
is used for grazing or recreation purposes)
Example; check-basins which irrigate individual trees in an orchard
6. Basin Irrigation
Basin irrigation is the most common form of surface irrigation, particularly in regions
with layouts of small fields.
If a field is level in all directions, is encompassed by a dyke to prevent runoff, and
provides an undirected flow of water onto the field
it is generally favored by moderate to slow intake soils, deep-rooted and closely
spaced crops
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8. Border Irrigation
The field is divided into sloping borders
Water is applied to individual borders from small hand-dug checks from the field
head ditch
It is suitable for nearly any crop except those that require prolonged ponding
9. Furrow Irrigation
Furrow irrigation avoids flooding the entire field surface by channeling the flow along
the primary direction of the field using 'furrows,'
Water infiltrates through the wetted perimeter and spreads vertically and
horizontally to refill the soil reservoir.
It provide better on-farm water management
11. 5.2 Pressurized irrigation
Pressurized irrigation has revolutionized the way we water plants.
Water is put into pipes, pressurized and precisely delivered to plants
Advantages
It saves much more water than traditional surface flow irrigation
according to FAO (2000), open irrigation application efficiency is 45 to 60%. In
contrast, pressurized irrigation efficiency is 75 to 95 %
It allows the use of the small bodies of water (runoff from rain) that couldn't be
used in traditional irrigation methods
valuable in arid and semi-arid areas
Disadvantages
Water dissolved minerals leads to frequent blocking of emitters
Build-up of mineral salts in the soil around root zones
12. Types of pressurized irrigations
a, Sprinkler Irrigation
Sprinkler irrigation is a method of applying water to the surface of the soil in the form of a
spray(similar to natural rainfall)
Water is distributed through a system of pipes usually by pumping
Adaptability of Sprinkler Irrigation
Some of the conditions which favour sprinkler irrigation are:
Soils too porous for good distribution by surface methods
Shallow soils whose topography prevents proper levelling for surface irrigation methods
Land having steep slopes and easily erodible soils
Irrigation stream too small to distribute water efficiently by surface irrigation
Undulating land too costly to level sufficiently for good surface irrigation
Soils with low water holding capacity and shallow rooted crops which require frequent
irrigation
13. Sprinkler Irrigation versus Surface irrigation
Frequent and small depth of water can readily be applied by sprinkler systems
Higher water application efficiency can normally be obtained by sprinkler irrigation
Water measurement is easier with sprinkler than with surface methods
Limitations 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 low infiltration rate cannot be irrigated efficiently in hot windy
areas
In areas of high temperature and high wind velocity, considerable evaporation losses of
water may take place
14. Types of sprinklers and Sprinkler systems
Classification based on the method of developing pressure:
Pump powered system
Gravity sprinkler system
Hybrid systems (Pumps + Gravity)
Classification based on portability and make-up of units:
1. Conventional system (Periodic move and fixed systems)
D/t types under this group based on portability and mobility of the d/t components
are;
Permanent system
Solid set system
Portable system
Hand move (semi portable system)
15. Fig. Lay out of Hand move sprinkler System
2. Mobile sprinkler machines
These are self propelled machines which are external power unit, designed
mobile with all required system components to irrigate larger area.
In these systems labor requirement is very less
16. Sprinkler System Components
A typical sprinkler irrigation system consists of the following components:
Pressure generating units(Pump unit): it is usually a centrifugal pump which takes
water from the source and provides adequate pressure for delivery into the pipe
system
Water carrier units (Mainlines , sub mainlines, Laterals):
Mainlines: it is a line b/n the source of pressurized water and the point at which
water is delivered to the field
Laterals: it comes out of the mainline to deliver water to the sprinkler nozzles
water delivery units (riser pipes and Sprinklers):
Quality improvement sub units ( Screens , Desilting basins):
Ancillary units ( Fertilizer and other chemical applicator):
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18. b, drip irrigation
Drip irrigation(trickle irrigation) involves dripping water onto the soil at very low
rates (2-20 litres/hour)
Water is applied close to plants so that only part of the soil in which the roots grow is
wetted
suitable for row crops (vegetables, soft fruit), tree and vine crops
It is adaptable to any farmable slope
On clay soils water must be applied slowly to avoid surface water ponding and
runoff.
On sandy soils higher emitter discharge rates will be needed to ensure adequate
lateral wetting of the soil
A typical drip irrigation system consists of the following components:
-Pump unit -Control head
-Main and sub main lines -Laterals
-Emitters or drippers
19. Unlike surface and sprinkler irrigation, drip irrigation only wets part of the soil root zone
Figure 5.11 Wetting patterns for sand and clay soils with high and low discharge rate
20. 5.3 Criteria for Selection of Various Methods
Surface, Sprinkler or Drip Irrigation
The suitability of the various irrigation methods, i.e. surface, sprinkler or drip
irrigation depends mainly on the following factors:
Natural conditions (soil type, slope, climate, water quality and availability)
Type of crop; Surface irrigation can be used for all types of crops. Sprinkler and
drip irrigation, b/s of their high capital investment per hectare
Type of technology; drip and sprinkler irrigation are technically more complicated
methods
Previous experience with irrigation; The choice of an irrigation method also
depends on the irrigation tradition within the region/country
required labor inputs; Surface irrigation often requires a much higher labor input
for construction, operation and maintenance - than sprinkler or drip irrigation
Costs and benefits;
