Chapter 5 methods of irrigation Dr. Thomas Abraham_19-3-14
Irrigation Methods are mainly classified into :
1. Surface Irrigation or Gravity Irrigation
2. Subsurface Irrigation or Sub-irrigation
3. Sprinkler or overhead irrigation
4. Drip or Trickle irrigation
1) SURFACE IRRIGATION
Irrigation water flows across the field to the point of
Primarily used for field crops and orchards
Water is applied to the soil surface and the water
flows by gravity either through furrows, strips or
Water is applied from a channel located at the upper
reach of the field.
Loss of water by conveyance and deep percolation is
high and the efficiency of irrigation is only 40-50%
at field level in surface method of irrigation.
Properly constructed water distribution systems to
give sufficient control of water to the fields
And effective land preparation to permit uniform
distribution of water over the field are very
Water is applied to the field in either the controlled or
Controlled: Water is applied from the head ditch and
guided by corrugations, furrows, borders, or ridges.
Uncontrolled: Wild flooding.
Surface irrigation is entirely practised where water is
Low initial cost of development is later offset by high
labour cost of applying water.
Deep percolation, runoff and drainage problems
Furrow irrigation - in which the water
poured on the field is directed to flow
through narrow channels dug between
the rows of crops, instead of distributing
the water throughout the whole field
The furrows must all have equal
dimensions, in order to guarantee that
the water is distributed evenly.
Like flood irrigation, furrow irrigation is
rather cheap in areas where water is
In furrow irrigation, only a part of the land
surface (the furrow) is wetted thus minimizing
Irrigation can be by corrugation using small
Furrow irrigation is adapted for irrigating on
various slopes except on steep ones because of
erosion and bank overflow.
There are different ways of applying water to the furrow.
As shown in Fig 3.1, siphons are used to divert water
from the head ditch to the furrows.
There can also be direct gravity flow whereby water is
delivered from the head ditch to the furrows by cutting
the ridge or levee separating the head ditch and the
Gated pipes can also be used. Large portable pipe(up
to 450 mm) with gate openings spaced to deliver water
to the furrows are used.
Water is pumped from the water source in closed
The openings of the gated pipe can be regulated to
control the discharge rate into the furrows.
The Major Design Considerations in Surface
Storing the Readily Available Moisture in the Root
Zone, if Possible;
Obtaining As Uniform Water Application As Possible;
Minimizing Soil Erosion by Applying Non-erosive
Minimizing Runoff at the End of the Furrow by Using
a Re-use System or a Cut -Back Stream;
Minimizing Labour Requirements by Having Good
Facilitating Use of Machinery for Land Preparation,
Cultivation, Furrowing, Harvesting Etc.
The Specific Design Parameters of Furrow
Irrigation Are Aimed at Achieving the Above
Objectives and Include:
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 wetting, and to
accommodate the track of mechanical
The range of spacing commonly used is from
0.3 to 1.8 m with 1.0 m as the average.
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).
Soil Type Maximum slopes*
Sandy loam 0.40
Fine sandy loam 0.50
Source: Withers & Vipond (1974)
*A minimum slope of about 0.05 % is required to
ensure surface drainage.
In this, Parallel ridges are made to guide a sheet of
flowing water when the water moves down the slope.
The field is divided into several long parallel strips
called borders that are separated by low ridges.
Field should be even surface over which the water can
flow down the slope with a nearly uniform depth.
Every strip is independently irrigated by turning a
stream of water at the upper end.
Then water spreads and flows down the strip in a thin
Water moves towards the lower end without erosion
covering the entire width of the border.
Sufficient moisture is provided to the soil to entire
length of the border.
Border method is suitable for most of the soils, while
it is best suited for soils having moderately low to
high infiltration rates.
However, it is not suitable for course sandy and clay
Border Irrigation System
In a border irrigation, controlled surface flooding is
practised whereby the field is divided up into strips by
parallel ridges or dykes and each strip is irrigated
separately by introducing water upstream and it
progressively covers the entire strip.
Border irrigation is suited for crops that can withstand
flooding for a short time e.g. wheat.
It can be used for all crops provided that the system
is designated to provide the needed water control for
irrigation of crops.
It is suited to soils between extremely high and very
low infiltration rates.
Border Irrigation Contd.
In border irrigation, water is applied slowly.
The root zone is applied water gradually
down the field.
At a time, the application flow is cut-off to
reduce water loses.
Ideally, there is no runoff and deep
The problem is that the time to cut off the
inflow is difficult to determine.
Basin method of irrigation is adopted mainly in
Usually round basins are made for small trees and
square basin for large trees.
These basins allow more water to be impounded
as the root zones of orchard plants are usually
Each basin is flooded and water is allowed to
infiltrate into the soil.
Based on type of crop and soil, nearly 5-10 cm
depth of water may be needed for every irrigation.
The advantage of basin method is that unskilled
labour can be used as there is no risk of erosion.
Disadvantages : there is difficulty in using modern
machinery and it is also labour intensive.
Basin irrigation is suitable for many field crops.
Rice grows best when its roots are submerged in
water and so basin irrigation is the best method
to use for this crop.
Other crops which are suited to basin irrigation
Pastures, e.g. alfalfa, clover;
Crops which are broadcast, such as cereals, and
To some extent row crops such as tobacco.
Size of Basins
The size of basin is related to stream size and soil type(See
Table : 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
60 216 0.04 0.12 0.24
90 324 0.06 0.18 0.36
120 432 0.08 0.24 0.48
150 540 0.10 0.30 0.60
180 648 0.12 0.36 0.72
210 756 0.14 0.42 0.84
240 864 0.16 0.48 0.96
300 1080 0.20 0.60 1.20
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
Most common among surface irrigation
Suitable for close growing crops like
groundnut, wheat, finger millet, pearl millet,
In this method field is divided into small plots
surrounded by bunds on all four sides.
Water from head channel is supplied into the
field channel one after the other.
Each field channel supplies water to two rows
of check basins and water is applied to one
basin after other.
In this, field is laid out into long, narrow,
strips, bordering with small bunds.
Most common size of strips are 30-50 m
length and 3-5 m width.
Borders are laid out along the general
Water from the channel is allowed into
each strip at a time.
This method is suitable for close growing
crops and medium to heavy textured
Not suitable for sandy soils.
It should be applied only to flat lands that
do not concave or slope downhill so that
the water can evenly flow to all parts of the
Yet even so, about 50% of the water is
wasted and does not get used by the crops.
Some of this wasted water accumulates at
the edges of a field and is called run-off.
In order to conserve some of this water,
growers can trap the run-off in ponds and
reuse it during the next round of flood
In flood irrigation, a large amount
of water is brought to the field
and flows on the ground among
In regions where water is
abundant, flood irrigation is the
This low tech irrigation method is
commonly used by societies in
However a large part of the wasted water can not
be reused due to massive loss via evaporation and
One of the advantages of flood irrigation is its
ability to flush salts out of the soil, which is
important for many saline intolerant crops.
However, the flooding causes an anaerobic
environment around the crop which can increase
microbial conversion of nitrogen from the soil to
atmospheric nitrogen, or denitrification, thus
creating low nitrogen soil.
Surge flooding is an attempt at a more efficient
version of conventional flood irrigation in which
water is released onto a field at scheduled times,
thus reducing excess run-off.
- Irrigation to crops by applying water
from beneath the soil surface either by
constructing trenches or installing
underground perforated pipe lines.
In this system, water is discharged
And allowed to stand during the whole
period of irrigation for lateral and
upward movement of water by
capillarity to wet the soil between the
Conditions that favor subsurface irrigation
An impervious subsoil at a depth of 2 m or more.
A very permeable subsoil of reasonably uniform texture
permitting good lateral and upward movement of water.
Permeable loam or sandy loam surface soil.
Uniform topographic conditions and moderate slope.
Existence of high water table.
Irrigation water is scarce and costly.
Soils should be free of any salinity problem.
It must be ensured that no water is lost by deep
Subsurface irrigation is made by constructing a series of
ditches or trenches 60 to 100 cm deep.
Width of the trenches is about 30 cm and vertical.
Spacing between the trenches varies between 15 to 30 m
depending on soil types and lateral movement of water in
Various types of crops, particularly with
shallow root systems are well adapted to
subsurface irrigation system.
Wheat, potato, beet, peas, fodder crops etc.
Maintenance of soil water at favorable tension
Loss of water by evaporation is held at
Can be used for soils with low water holding
capacity and high infiltration rate where
surface irrigation methods cannot be adopted
and sprinkler irrigation is expensive.
Presence of high water table.
Poor quality irrigation water cannot be
used-good quality water must be
Chances of saline and alkali conditions
being developed by upward movement
of salts with water.
Soils should have a good hydraulic
conductivity for upward movement of
Sprinkler irrigation is a method of applying irrigation
water which is similar to natural rainfall.
Water is distributed through a system of pipes usually
Water under pressure is carried and sprayed into the air
above the crop through a system of:
Overhead perforated pipes, nozzle lines, or through
nozzles fitted to riser pipes attached to a system of
pipes laid on the ground.
Nozzles of fixed type or rotating under the pressure of
water are set at suitable intervals in the distribution
Sprayed water wets both the crop and the soil and,
hence, has a refreshing effect.
Water is applied at a rate less than the intake rate of
soil so that there is no runoff.
Measured quantity of water is applied to meet the soil
Sprinkler irrigation is suited for most row, field
and tree crops and water can be sprayed over or
under the crop canopy.
Large sprinklers are not recommended for
irrigation of delicate crops such as lettuce because
the large water drops may damage the crop.
Sprinkler irrigation is adaptable to any farmable
slope, whether uniform or undulating.
Lateral pipes supplying water to the sprinklers
should always be laid out along land contour.
This will minimize the pressure changes at the
sprinklers and provide a uniform irrigation.
Sprinklers are best suited to sandy
soils with high infiltration rates
although they are adaptable to most
Application rate from the sprinklers (in
mm/hour) is always chosen to be less
than the basic infiltration rate of the
soil - so that surface ponding and
runoff can be avoided.
Sprinklers are not suitable for soils
which easily form a crust.
A typical sprinkler irrigation system consists of
the following components:
Suitable irrigation water
A good clean supply of water, free of suspended
sediments, to avoid problems of sprinkler
nozzle blockage and spoiling the crop by
coating it with sediment.
Sprinkler irrigation (cont..)
• Uniform application by “artificial rain”
• Good application efficiencies (0.7 – 0.8)
– dependent on wind, temperature, humidity
• Fairly terrain independent (but design must
take terrain into account)
• Can have a low labour content
• High(ish) investment cost
• High maintenance cost due to pumping
• Can be complex to run
Sprinkler irrigation: Criteria
• Must permit cost recovery within one to two
years (and double investment in a short time)
• Must be suitable for use on small and irregular
• Must require only simple maintenance and tools
• Have a low risk of component failure
• Be simple to operate
• Be durable and reliable – able to withstand
rough and frequent handling without serious
Sprinkler irrigation: Appropriateness
Type Score Crops
Piped distribution 16 All
“Low tech” 16 All
Drag hose 15 All
Solid set 14 Orchards
Hand move laterals 12 All
Perforated pipe 11 Soft fruit and veg
Static gun 10 Cereals, Row crops
Side roll 7 Short cereals, row crops
Traveling gun 7 Cereals, Row crops
Boom 6 Cereals, Row crops
Centre pivot 5 Cereals, Row crops
Linear move 5 Cereals, Row crops
Side move 4 Cereals, Row crops
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
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
Etc. - See text for other considerations
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
Select a Pipe Size which limits the total pressure
change to 20% of the design operating pressure of
This limits overall variations in Sprinkler
Discharge to 10%.
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)
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.
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
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.
Maximum Discharge (Qp) = qs N
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
DRIP OR TRICKLE IRRIGATION
3.4.1 Introduction: In this irrigation system:
i) Water is applied directly to the crop ie. entire field is
ii) Water is conserved
(iii) Weeds are controlled because only the places
getting water can grow weeds.
(iv) There is a low pressure system.
(v) There is a slow rate of water application somewhat
matching the consumptive use. Application rate can be
as low as 1 - 12 l/hr.
(vi) There is reduced evaporation, only potential
transpiration is considered.
vii) There is no need for a drainage system.
Drip irrigation / trickle irrigation - involves
dripping water onto the soil at very low rates
-from a system of small diameter plastic
pipes fitted with outlets called emitters or
Water is applied close to plants so that only
part of the soil in which the roots grow is
wetted (Figure 60 in Notes).
With drip irrigation water, applications are
more frequent (usually every 1-3 days).
This provides a very favourable high moisture
level in the soil in which plants can flourish.
Drip Irrigation System
• The Major Components of a Drip Irrigation
• a) Head unit which contains filters to
remove debris that may block emitters;
fertilizer tank; water meter; and pressure
• b) Mainline, Laterals, and Emitters which
can be easily blocked.
Water Use for Trickle Irrigation System
• The design of drip system is similar to that of
the sprinkler system except that the spacing of
emitters is much less than that of sprinklers
and that water must be filtered and treated to
prevent blockage of emitters.
• Another major difference is that not all areas
• In design, the water use rate or the area
irrigated may be decreased to account for this
While drip irrigation may be the most expensive method of
irrigation, it is also the most advanced and efficient method in
respect to effective water use.
Usually used to irrigate fruits and vegetables
System consists of perforated pipes that are placed by rows of
crops or buried along their root lines and emit water directly onto
the crops that need it.
As a result, evaporation is drastically reduced and 25% irrigation
water is conserved in comparison to flood irrigation.
Drip irrigation also allows the grower to customize an irrigation
program most beneficial to each crop.
Fertigation is possible.
Caution : Water high in salts / sediments should be filtered -
otherwise they may clog the emitters and create a local buildup
of high salinity soil around the plants if the irrigation water
contains soluble salts.
Drip irrigation is most suitable for
row crops (vegetables, soft fruit),
tree and vine crops where one or
more emitters can be provided for
Generally only high value crops are
considered because of the high
capital costs of installing a drip
Drip irrigation is adaptable to any
Normally the crop would be planted
along contour lines and the water
supply pipes (laterals) would be laid
along the contour also.
This is done to minimize changes
in emitter discharge as a result of
land elevation changes.
Drip irrigation is suitable for most
On clay soils water must be applied
slowly to avoid surface water ponding
On sandy soils higher emitter
discharge rates will be needed to
ensure adequate lateral wetting of the
One of the main problems with drip irrigation is
blockage of the emitters.
All emitters have very small waterways ranging
from 0.2-2.0 mm in diameter and these can
become blocked if the water is not clean.
Thus it is essential for irrigation water to be free of
]If this is not so then filtration of the irrigation
water will be needed.
Blockage may also occur if the water contains
algae, fertilizer deposits and dissolved chemicals
which precipitate such as Ca and Fe.
Filtration may remove some of the materials but
the problem may be complex to solve and requires
an experienced professional.
SOIL TYPE AND WATER MOVEMENT.
THE APPLICATION OF WATER IS BY
A typical drip irrigation system is
shown in Figure 61 and consists
of the following components:
Emitters or drippers.
Pump unit takes water from the source and
provides the right pressure for delivery into the
The control head consists of valves to control the
discharge and pressure in the entire system.
It may also have filters to clear the water.
Common types of filter include screen filters and
graded sand filters which remove fine material
suspended in the water.
Some control head units contain a fertilizer or
These slowly add a measured dose of fertilizer into
the water during irrigation.
This is one of the major advantages of drip
irrigation over other methods.
Supply water from the control head into the fields.
They are usually made from PVC or polyethylene hose and
should be buried below ground because they easily
degrade when exposed to direct solar radiation.
Lateral pipes are usually 13-32 mm diameter.
Emitters or drippers are devices used to control the
discharge of water from the lateral to the plants.
They are usually spaced more than 1 metre apart with one
or more emitters used for a single plant such as a tree.
For row crops more closely spaced emitters may be used to
wet a strip of soil.
Many different emitter designs have been produced in
The basis of design is to produce an emitter which will
provide a specified constant discharge which does not vary
much with pressure changes, and does not block easily.
The water savings that can be made using drip
irrigation are the reductions in deep percolation,
in surface runoff and in evaporation from the
These savings, it must be remembered, depend
as much on the user of the equipment as on the
Drip irrigation is not a substitute for other
proven methods of irrigation.
It is just another way of applying water.
It is best suited to areas where water quality is
marginal, land is steeply sloping or undulating
and of poor quality, where water or labour are
expensive, or where high value crops require
frequent water applications.
Water Use for Trickle Irrigation
Karmeli and Keller (1975) suggested the
following water use rate for trickle irrigation design
ETt = ET x P/85
Where: ETt is average evapotranspiration rate for crops under
P is the percentage of the total area shaded by crops;
ET is the conventional evapotranspiration rate for the crop. E.g.
If a mature orchard shades 70% of the area and the
conventional ET is 7 mm/day, the trickle irrigation design rate is:
7/1 x 70/85 = 5.8 mm/day
OR use potential transpiration, Tp = 0.7 Epan where Epan is the
evaporation from the United States Class A pan.
Consist of fixed type and variable size types.
The fixed size emitters do not have a
mechanism to compensate for the friction
induced pressure drop along the lateral while
the variable size types have it.
Emitter discharge may be described by:
q = K h x
Where: q is the emitter discharge; K is
constant for each emitter ; h is pressure head
at which the emitter operates and x is the
exponent characterized by the flow regime.
Water Distribution from Emitters
Emitter discharge variability is greater than that of
sprinkler nozzles because of smaller openings(lower
flow) and lower design pressures.
Eu = 1 - (0.8 Cv/ n 0.5 )
Where Eu is emitter uniformity; Cv is manufacturer's
coefficient of variation(s/x ); n is the number of
emitters per plant.
Application efficiency for trickle irrigation is
Eea = Eu x Ea x 100
Where Eea is the trickle irrigation efficiency; Ea is the
application efficiency as defined earlier.
Pressure Head at Manifold Inlet
Like Sprinklers, the pressure head at inlet to
= Average Operating Head = 8.9 m
+ 75% of Lateral and Manifold head Loss =
0.75 (0.51 + 0.68)
+ Riser Height = Zero for Trickle since no
+ Elevation difference = Zero , since the field is
= 9.79 m
Total Head for Pump
= Manifold Pressure = 9.79 m
+ Pressure loss at Sub-main = 6.59 m
+ Pressure loss at Main = 2.90 m
+ Suction Lift = 20 m
+ Net Positive Suction head for pump = 4 m
= 43.28 m
i.e. The Pump must deliver 3.23 L/s at a head of
about 43 m.
Applied in places where natural soil and
topographic condition favour water
application to the soil under the surface, a
practice called sub-surface irrigation.
These conditions include:
a) Impervious layer at 15 cm depth or
b) Pervious soil underlying the restricting
c) Uniform topographic condition
d) Moderate slopes.
SUB-SURFACE IRRIGATION (Contd…)
The operation of the system involves a
huge reservoir of water and level is
controlled by inflow and outflow.
The inflow is water application and rainfall
while the outflow is evapotranspiration
and deep percolation.
It does not disturb normal farm
operations. Excess water can be removed