Everything You Need to Know About Irrigation Methods and Water Requirements

Swami Keshvanand Institute of Technology
Management & Gramothan Jaipur
SITARAM SAINI
ASSISTANT PROFESSOR
CIVIL ENGG.SKIT
INTRODUCTION
ABOUT
IRRIGATION

 What is irrigation?
 Irrigation is defined as the process of artificially
supplying water to soil for raising crops.
 A crop requires a certain amount of water at some
fixed time interval throughout its period of growth.
 If the water requirement of crop is met by natural
rainfall during the growth period, there is no need of
irrigation.

 Necessity of Irrigation
 Increase in crop yield
 Protection from famine
 Cultivation of crash crops
 Elimination of mixed cropping
 Increase in the wealth of country
 Increase in prosperity of people
 Generation of hydro-electric power
 Domestic and industrial water supply
 Inland navigation
 Communication facility
 Canal plantation
 Increase in ground water storage
 Overall development of the country
 Aid in civilization

4
Surface
irrigation
Sub-surface
irrigation
Sprinkler
irrigation
Flooding
method method
Furrow Contour
farming
Wild
flooding
Controlled
flooding
Free
flooding
Contour
laterals
Border
strips
Check Basin
flooding flooding
Zig-zag
method
Drip
irrigation

Factors affecting choice of irrigation method
 The selection of the irrigation method is based on the
following factors.
1. Soil characteristics of the land to be irrigated.
2. Topography of the area.
3. The available water supply.
4. Type of crop and its requirements.
5. Size of the stream supplying irrigation water.
6. Amount of water required in each irrigation.

 Surface irrigation method.
Surface Irrigation
Flooding
method
Furrow
method
Contour
method
Wild
flooding
Controlled
flooding
Free
flooding
Contour Border Check Basin
laterals strips flooding flooding
Zig-zag
method

 Surface irrigation method.
 In surface irrigation methods, the irrigation water is
applied by spreading in the form of sheet or small
streams on the lands to be irrigated.
 The surface irrigation is further divided as follows:
1) Flooding method.
2) Furrow method .
3) Contour farming.

 Surface irrigation methods.
 All the above methods of the surface irrigation
are adopted for the perennial irrigation system.
 The inundation irrigation system adopts only the
wild or uncontrolled flooding method of irrigation.

 Wild flooding method.
 Wild flooding method is the earliest and the primitive
method of application of water to the land.
 In this method the water is applied by spreading it
over the land prior to the application of water, no land
preparations is done in the form of border or field
ditches.
 The water is allowed to flow the natural slope of the
land.

 Controlled flooding.
 In controlled flooding methods irrigation water is
applied by spreading it over the land to be irrigated
with proper control on the flow of water as well as the
quantity of water applied.
 All the methods of control flooding require prior
preparation of the land.
 The land is properly graded & agricultural fields are
divided into small units by levees .

 Controlled flooding.
 The various methods of controlled flooding are:
1. Free flooding.
2. Contour laterals.
3. Border strips.
4. Check basins.
5. Basin flooding.
6. Zig-zag method.

 Free flooding.
 Free flooding consists of dividing the entire land to be
irrigated into small strips by a number of field channels
or levees known as laterals.
 These laterals may be either at right angles to the sides
of the field or at right angles to the contour lines .

 Contour laterals
This is a special case of free flooding in which the field
channels or laterals are aligned approximately along the
contour lines.
In this method, irrigation is possible only on side of the
laterals.

Border strips
In this method, the agricultural area is divided into
series of long narrow strips known as border strips by
levees, i.e. small bunds.
This method is suitable when the area is at level with
gentle slope.

 Check flooding
In check flooding the crop area is divided into some plots
which are relatively leveled by checks or bunds.
Water from field channels is allowed to enter to each plot or
check basin and the plots are flooded to the required depth.

 Basin flooding
This method is used frequently to irrigate the plantations. It
is a special type of check flooding method.
Each plant is enclosed by circular channels which is called
basin. Basins are connected to small field ditches.
Ditches are fed from the main supply channel.

 Zig-zag method
In this method, the agricultural area is sub-divided into
small plots by low bunds in a zig-zag manner.
The wateris supplied to the plots from the field channel
through the openings.
The water flows in a zig-zag way to cover the entire area.
When the desired depth is attained, the openings are closed.

 Furrow method.
Furrow irrigation avoids flooding the entire field
surface by channeling the flow along the primary
direction of the field using ‘furrows,’‘grooves’,‘lines’.

 Contour farming
Contour farming is practiced in hilly areas with slopes
and with falling contour.
The land is divided into series of horizontal strips
called terraces.
Small bunds are constructed at the end of each terrace
to hold water up to equal height.

 Sub-Surface irrigation
method.
 Subsurface drip irrigation (SDI) is the irrigation of
crops through buried plastic tubes containing
embedded emitters located at regular spacings.
surface irrigation method consists of
water directly to the root zone of the
 The sub
supplying
plants.

method.
 The favourable conditions for sub surface irrigation:
1. Moderate slope.
2. Uniform topographic condition.
3. Good quality of irrigation water .
4. Impervious sub-soil at reasonable depth. (i.e. 2-3
m depth).

method.
 The subsurface irrigation methods can be classified
as follows:
1. Natural sub-surface irrigation .
2. Artificial sub-surface irrigation.

Sprinkler Irrigation
Sprinkler irrigation is a method of applying irrigation
water which is similar to natural rainfall.
Water is distributed through a system of pipes usually
by pumping. It is then sprayed into the air through
sprinklers so that it breaks up into small water drops
which fall to the ground.

 Drip Irrigation.
 Drip irrigation is also known as trickle irrigation .
 It is one of the latest developed methods of irrigation
which is more popular in the regions facing scarcity
of water.
 This method was first introduced in Israel.
 In India this method is more useful in areas in
Gujarat, Maharashtra, Kerala, & Karnataka.

 Drip irrigation layout and its parts.

Sr.
No.
Name of the soil group Grain size diameter in mm
1 Gravelly Soil 60 to 2
2 Sandy Soil 2 to 0.5
3 Silty Soil 0.5 to 0.002
4 Clayey Soil <0.002

Water present in the soil may be
classified under three heads:
1.Hygroscopic water: When an oven dried
sample is kept open in the atmosphere, it
absorbs some amount of water from the
atmosphere. This is known as hygroscopic
water, and is not capable of movement by the
action of gravity or capillary forces.
2.Capillary water: Capillary water is that
part, in excess of hygroscopic water, which
exists in the pore space of the soil by
molecular attraction.
3.Gravitational water: Gravitational water is
that part in excess of hygroscopic and
capillary water which will move out of the
soil if favorable drainage is provided. 12

FactorsAffecting Water Requirements:
WaterTable
Depending upon position of water table to ground surface or much
below, water requirement may be less or more, respectively.
Climate
The evaporation loss in hot climate, hence, water requirement will be
more and in cold climate water requirement will beless.
Typeof soil
If soil is porous (i.e.sandy) water percolates quickly, retention of water is
less, therefore, water requirement is more. But in clayey soil, water
requirement is less.
Methodof Ploughing
In deep ploughing, soil can retain water for a longer period and water
requirement is less.

Intensity of Irrigation
Intensity of irrigation means the ratio of area under
cultivation to the total culturable area. If this intensity
is more, more area is under cultivation, hence water
requirement ismore.
Ground slope
In steep ground water flows down quickly, finds little time to
absorb required amount of water, hence, water
requirement is more. For flat slope, water flows slowly, finds
enough time for absorption, hence, water requirement is
less.
Method of applicationof water
In surface flow irrigation, evaporation is more and in sub-
surface irrigation, evaporation loss is minimum. Hence,
water requirement is more in surface irrigation than sub-
surface irrigation.

The field capacity of soil is the moisture content after the
drainage of gravitational water has become very slow and the
moisture content has become relatively stable.
This situation usually exists for one to three days after the
soil has been thoroughly wetted by rain or irrigation.
At field capacity, the large soil pores are filled with air, the
micro pores are filled with water and any further drainage is
slow.
The field capacity is the upper limit of available moisture
range in soil moisture and plant relations.

Permanent wilting point or the wilting coefficient
is that water content at which plants can no longer
extract sufficient water from the soil for its growth.
If the natural rain is sufficient and timely so as to
satisfy both these requirements, no irrigation water is
required for raising that crop.

Crop Period or Base Period
The time period that elapses from the instant of its
sowing to the instant of its harvesting is called the
crop-period.
The time between the first watering of a crop at the
time of its sowing to its last watering before
harvesting is called the Base period.
Crop period is slightly more than the base
period, but for all practical purposes, they are taken
as one and the same thing, and generally expressed
in B days.
Definitions of some Common Important Terms:

The total area lying between drainage boundaries which can be
commanded or irrigated by a canal system or water course is known
as gross commanded area.
Culturable Commanded Area (CCA)
Gross commanded area contains some unfertile barren land, local
ponds, villages, graveyards etc which are actually unculturable areas.
The gross commanded area minus these unculturable area on which
crops can be grown satisfactorily is known as Culturable Commanded
Area.
 CCA = GCA – Unculturable Area

The area on which crop is grown at a particular
time or crop season.
Culturable Uncultivated Area
The area on which no crop is grown at a
particular time or crop season
Intensity of Irrigation (I.I)
Percentage of CCA that is cultivated in a
particular season.

 The distribution of water during the base period is not uniform,
since crops require maximum water during first watering after
the crops have grown a few centimeters.
During the subsequent watering the quantity of water needed
by crops gradually decreases and is least when crop gains
maturity.
The first watering is known as kor watering, and the depth
applied is known as kor depth.
The portion of the base period in which kor watering is needed
is known as kor period.
 While designing the capacity of a channel, kor water must be
taken into account since discharge in the canal has to be
maximum during this time.

The ratio of area irrigated in Rabi
season to that irrigated in Kharif season is
known as crop ratio.
The crop ratio is so selected that the
discharge in the canal during both the
seasons may be uniform.

The time factor of a canal is the ratio of the number of days the
canal has actually run to the number of days of irrigation period.
For example, if the number of days of irrigation period = 12,
and the canal has actually run for 5 days, the time factor will be
5/12.
 (Note: A day has a period of 24 hours (i.e. it includes the night
also).
Capacity factor
This is the ratio of the mean supply discharge to the full supply
discharge of a canal.

The total quantity of water required by the crop for
its full growth may be expressed in centimeter (inches)
or hectare-metre
This total depth of water (in cm) required by a crop
to come to maturity is called its delta (∆).

The duty of water is the relationship between the volume of
water and the area of the crop it matures.
This volume of water is generally expressed as, “a unit discharge
flowing for a time equal to the base period of the crop, called Base of
a duty”.
If water flowing at a rate of one cubic metre per second, runs
continuously for B days, and matures 200 hectares, then the duty of
water for that particular crop will be defined as 200 hectares per
cumec to the base of B days.
Hence, duty is defined as the area irrigated per cumec of
discharge running for base period B.

(i) At the head of main canal - known as Gross Quantity.
(ii) At the head of a branch canal - known as Lateral
Quantity.
(iii) At the outlet of a canal - known as Outlet Factor.
(iv) At the head of land, to be irrigated - known as Net
Quantity.

Let, base period of the crop be B days, and
one cumec of water be applied to this crop on the field for B days.
Now, volume of water applied to this crop during B days
= V = (1 x 60 x 60 x 24 x B) m3
= 86,400 B m3
By definition of duty (D), one cubic meter supplied for B days matures D
hectares of land.
:. This quantity of water (V) matures D hectares of land or 104D sq. m of area.
Total depth of water applied on this land
= Volume/area = 86400 B / 104D = 8.64 B / D metres
By definition, this total depth of water is called delta (∆),
∆ = 8.64 B / D meter ∆ = 864 B / D cm
17
where, ∆ is in cm, B is in days
;a
ate
nr
dRe
Dquir
ie
sm
dut
to
yfC
ir
nop
hs
ectares/cumec.

duty is 864
period of this
Find the delta for a crop when its
hectares/cumec on the field. The base
crop is 120 days.
Solution:
In this question,
B = 120 days; and D = 864 hectares/cumec
∆ = 864 B / D cm
= 864 x 120 / 864
= 120 cm

Methods and systems of irrigation;
Mode of applying water to the crops;
Methods of cultivation;
Time and frequency of tilling;
Types of the crop;
Base period of the crop;
Climatic conditions of the area;
Quality of water;
Method of assessment;
Canal conditions;
Character of soil and sub-soil of the canal;
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12. 32
Character of soil and suW
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e
tm
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ir
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as
tionfields.

 Suitable method of applying water to the crops should be
used.
The land should be properly ploughed and leveled before
sowing the crop.
The land should be cultivated frequently, since frequent
cultivation reduces loss of moisture specially when the
ground water is within capillary reach of ground surface.

The canals should be lined. This reduces seepage and
percolation losses. Also, water can be conveyed quickly,
thus reducing, evaporation losses.
Parallel canals should be constructed. If there are two
canals running side by side, the F.S.L. will be lowered,
and the losses will thus be reduced.
 The idle length of the canal should be reduced.
 The alignment of the canal either in sandy soil or in
fissured rock should be avoided.
The canal should be so aligned that the areas to be
cultivated are concentrated along it.

 The source of supply should be such that it gives
good quality of water.
 The rotation of crops must be practiced.
 Volumetric method of assessment should be used.
The farmers must be trained in the proper use of
water, so that they apply correct quantity of water at
correct timing.
 The land should be redistributed to the farmers so
that they get only as much land as they are capable
of managing it.

Research stations should be established in various
localities to study the soil, the seed and
conservation of moisture. The problems
concerning the economical use of water should be
studied at research stations.
The canal administrative staff should be efficient,
responsible and honest. The operation of the canal
system should be such that the farmers both at the
head of the canal as well as at the tail end get
water as and when they need it.

Efficiency is the ratio of the water output to the water input,
and is usually expressed as percentage. Input minus output is
nothing but losses, and hence, if losses are more, output is less
and, therefore, efficiency is less. Hence, efficiency is inversely
proportional to the losses.
Water conveyance Efficiency (ηc)
It is the ratio of the water delivered into the fields from the outlet
point of the channel, to the water pumped into the channel at the
starting point. It takes the conveyance or transit losses into
account.
r
c

Wf
Water diverted from the river or reservoir W
Water delivered to the farm
 

f
f f
a
W R  D 
s
 
Wf Wf
where
Rf  Surface runoff;Df  Deep percolation
W
Water application Efficiency (ηa)
It is the ratio of the quantity of water stored into the root zone of
the crops to the quantity of water delivered into the field. It may
also be termed as farm efficiency, as it takes into account the water
lost in the farm.
  Water stored in the root zone during irrrigation

Water storage Efficiency (ηs)
It is the ratio of the water stored in the root zone during irrigation
to the water needed in the root zone prior to irrigation ( i.e. field
capacity – existing moisture content ).
s
 Ws
Wn
Water needed in the root zone prior to irrigation
Water stored in the root zone during irrrigation
 

Water-use Efficiency (ηu)
It is the ratio of the water beneficially used, including leaching
water, to the quantity of water delivered.
u
 Wu
Wd
Water used consumptively
 

54
Irrigation Efficiencies
The effectiveness of irrigation may also be measured by its water
distribution efficiency), which is defined below:
where
d  average depth of water stored during irrigation;
y  average numerical deviation in depth of water stored from
average depth stored during irrigation
𝑑
= ( 1 -
𝑦
𝑑
)100

55
Irrigation Efficiencies
Wd
 Wcu

Net amount of water depleted from root zone soil water
Normal consumptive use of water

Crop Base period
(days)
Area
(hectares)
Duty at the field
(hectares/cumec)
Wheat 120 4800 1800
Sugar-cane 360 5600 800
Cotton 200 2400 1400
Rice 120 3200 900
Vegetables 120 1400 700

Crop
Base period
Duty at the
field D Delta Δ = Area
B (days) (ha/cumec) (8.64 B)/D (ha) (ha-m)
Wheat 120 1800 0.576 4800 2765.0
Sugar-cane 360 800 3.890 5600 21800.0
Cotton 200 1400 1.235 2400 2965.0
Rice 120 900 1.152 3200 3690.0
Vegetables 120 700 1.480 1400 2070.0
Total 33290
Therefore, capacity of the reservoir = 33290 / (0.8 x 0.88) =
47,300 ha-m

Q-2) An irrigation canal has gross commanded area of 80,000 hectares out
of which 85% is culturable irrigable. The intensity of irrigation for Kharif
season is 30% and for Rabi season is 60%. Find the discharge required at
the head of canal if the duty at its head is 800 hectares/cumec for Kharif
season and 1700 hectares/cumec for Rabi season.
Solution:
Gross culturable area = GCA = 80,000 hectares
Culturable commanded area = CCA = 0.85 x 80,000 = 68,000 hectares
Area under Kharif season = 68,000 x 0.30 = 20,400 hectares
Area under Rabi season = 68,000 x 0.60 = 40,800 hectares
Water required at the head of the canal in Kharif =Area/duty
= 20,400/800 = 25.5 cumecs
Water required at the head of the canal in Rabi =Area/duty
= 40,800/1700 = 24.0 cumecs
Since water requirement in Kharif is more so the canal may be designed to
carry a discharge of 25.5 cumecs.

Q-3) A watercourse has a culturable commanded area of 2600 hectares,
out of which the intensities of irrigation for perennial sugar-cane and rice
crops are 20% and 40% respectively. The duty for these crops at the head
of watercourse are 750 hectares/cumec and 1800 hectares/cumec
respectively. Find the discharge required at the head of watercourse if the
peak demand is 20% of the average requirement.
Solution:
Culturable commanded area = CCA = 2,600 hectares
Area under sugar-cane = 2600 x 0.2 = 520 hectares
Area under rice = 2600 x 0.4 = 1040 hectares
Water required for sugarcane = Area/duty = 520/750 = 0.694 cumecs
Water required for rice =Area/duty = 1040/1800 = 0.577 cumecs
Since sugar-cane is a perennial crop, it will require water throughout the year.
Hence,
Watercourse must carry a total discharge = 0.694 + 0.577
= 1.271 cumecs

Everything You Need to Know About Irrigation Methods and Water Requirements

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