Irrigation engineering module 1

 80% human body made
up of water.
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Dr. L. S. Thakur

On average we have sufficient water to meet human
needs. The problem is water distribution.
We distinguish between water quality and quantity
problems.
75% earth’s surface covered with water, only 3%, is fresh.,
with only 1% water available for human consumption.
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Region Total Population
w/o Access to
Water (%)
Absolute No. of People
w/o Access to Water
(in millions)
Africa 54 381
Latin America & Caribbean 20 97
Asia & Pacific 20 627
Western Asia 12 10
Total 26 1115
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Dr. L. S. Thakur
C i v i l E n g i n e e r i n g D e p a r t m e n t
B I T S e d u c a m p u s
w w w . l a l i t s t h a k u r . c om
Irrigation Engineering
Module 1
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Outline
Necessity of irrigation
Scope of irrigation engineering
Benefits and ill effects of irrigation
Irrigation development in India
Types of irrigation systems
Soil-water plant relationship: Classification of soil
water- soil moisture contents- depth of soil water available
to plants-permanent and ultimate wilting point
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What is Irrigation Engineering
 Irrigation is the artificial application of water to the
soil for the purpose of supplying the moisture
essential for plant growth
 It is used to assist in growth of agricultural crops,
maintenance of landscapes, and revegetation of
disturbed soils in dry areas and during periods of
inadequate rainfall.
 Irrigation is often studied with drainage, i.e. the
natural or artificial removal of surface and sub-
surface water from a given area.
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What is Irrigation Engineering
Irrigation engineering:
involves
 Conception,
 Planning,
 Design,
 Construction,
 Operation and
 Management of an
irrigation system.
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Historical Perspectives
 Ancient civilizations rose over irrigated areas
 Egypt claims having the world's oldest dam, 108m
long, 12m high, built 5,000 years ago
 6,000 years ago, Mesopotamia supported as many
as 25 million people.
 The same land today with similar population
depends on imported wheat for food
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Historical Perspectives
 Nile River Basin (Egypt) - 6000 B.C.
 Tigris-Euphrates River Basin (Iraq, Iran, Syria) - 4000
B.C.
 Yellow River Basin (China) - 3000 B.C.
 Indus River Basin (India) - 2500 B.C.
 Maya and Inca civilizations (Mexico, South America) -
500 B.C.
 Salt River Basin (Arizona) - 100 B.C.
 Western U. S. - 1800’s
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Necessity of Irrigation
 Insufficient rainfall
 Uneven distribution of rainfall
 Improvement of perennial crop
 Development of agriculture in desert area
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Challenges for Irrigation & Drainage Engineers
 Depletion of natural resources (soil and water)
 Salinization of soil
 Lower productivity of soil: tax records from
Mesopotamia barely yields were 2500L/ha, now only
¼ to ½ this value.
 Dissertification
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Benefits of Irrigation
 Increase in crop yield
 Protection from famine
 Cultivation of superior crops
 Elimination of mixed cropping
 Economic development
 Hydro power generation
 Domestic and industrial water supply
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Disadvantages/ Ill – Effects of Irrigation
 Rising of water table
 Formation of marshy
land
 Dampness in weather
 Loss of valuable lands
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Irrigation & Technology
 Hi-tech control: tensiometers, controls and
automation of irrigation and water application.
 Use of remote sensing for irrigation scheduling and
prediction of yield
 New job oppurtunities
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Role of Civil Engineers
 The supply of water at farm turnout
 Water storage
 Water conveyance
 Supplying water WHEN needed and by the
QUANTITY needed – irrigation scheduling
 Drainage: surface and sub-surface
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Purposes of Irrigation
 Providing insurance against short duration droughts
 Reducing the hazard of frost (increase the
temperature of the plant)
 Reducing the temperature during hot spells
 Washing or diluting salts in the soil
 Softening tillage pans and clods.
 Delaying bud formation by evaporative cooling
 Promoting the function of some micro organisms
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Different Uses of Water
 consumptive usage is diversion + consumption of water
through transforming it into water vapor (where it is “lost”
to the atmosphere), letting it seep into ground, or
significantly degrading its quality. For eg.: Residential,
Industrial, Agricultural, Forestry
 non-consumptive usage Do not reduce water supply &,
frequently, do not degrade water quality. Examples:
Fisheries use water as a medium for fish growth,
Hydroelectric users extract energy from water, Recreation
may involve using water as a medium (example: swimming)
and/or extracting energy from water (examples: white-
water rafting, surfing), Transportation is especially
important use of water in the tropics.
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Irrigation Development in India
 Among Asian countries India has largest arable land
(40%).
 Only USA has more arable land than India.
 In a monsoon climate and an agrarian economy like
India, irrigation has played a major role in the
production process. There is evidence of the practice
of irrigation since the establishment of settled
agriculture during the Indus Valley Civilization
(2500 BC).
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 These irrigation technologies were in the form of
small and minor works, which could be operated by
small households to irrigate small patches of land
and did not require co-operative effort.
 In the south, perennial irrigation may have begun
with construction of the Grand Anicut by the Cholas
as early as second century to provide irrigation from
the Cauvery river.
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 At beginning of 19th century, there was large no of
water tanks in peninsular India and several canals in
northern India were build.
 The upper Ganga canal, upper Bari Doab canal and
the Krishna and Godavari delta system were
constructed between 1836-1866.
 During the last fifty years, gross irrigated area (GIA)
of India has increased more than three fold from 22
to 76 million Hectares.
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 Groundwater irrigation in India developed during
the period of green revolution and contributed much
in increasing the gross irrigated area of the country.
 In the last five decades, groundwater irrigation has
increased from 5 million hectares to 35million
hectares.
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Classification of Irrigation Schemes
 Irrigation projects in India are classified into three
categories
 major
 medium &
 minor
according to the area cultivated.
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 Major irrigation projects: projects which have a
culturable command area (CCA) of more than
10,000 ha but more than 2,000 ha utilize mostly
surface water resources.
 Medium irrigation projects: projects which have CCA
less than 10,000 ha. But more than 2,000 ha utilizes
mostly surface water resources.
 Minor irrigation projects: projects with CCA less
than or equal to 2,000 ha. utilizes both ground water
and local surface water resources.
Classification of Irrigation Schemes
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National Water Policy
 Our country had adapted a national water policy in
the year 1987 which was revised in 2002.
 The policy document lays down the fact that
planning and development of water resources should
be governed by the national perspective.
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Aspects Related to Irrigation from Policy
 Irrigation planning either in an individual project or in a
watershed as a whole should take into account irrigability of
land, cost-effective irrigation options possible from all
available sources of water and appropriate irrigation
techniques for optimizing water use efficiency.
 close integration of water use and land use policies.
 Water allocation in an irrigation system should be done with
due regard to equity and social justice.
 Concerted efforts should be made to ensure that the
irrigation potential created is fully utilised.
 Irrigation being the largest consumer of fresh water, the aim
should be to get optimal productivity per unit of water.
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Types of Irrigation Systems
Irrigation
Systems
Flow
Irrigation
Perennial
Irrigation
Inundation
Irrigation
As Per Sources
Direct
Irrigation eg.
Weir
Storage
Irrigation eg.
Dam
Combined
Irrigation eg.
Dam & Weir
Lift Irrigation
Well Irrigation
Lift Canal
Irrigation
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Based on way water is applied to agricultural
land
 Flow irrigation system: where the irrigation water is
conveyed by growing to the irrigated land.
 Direct irrigation
 Reservoir/tank/storage irrigation
 Lift irrigation system: irrigation water is available at a
level lower than that of the land to be irrigated and hence
water is lifted up by pumps or by other mechanical
devices for lifting water and conveyed to the agricultural
land through channels flowing under gravity.
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On the basis of duration of the applied water
 Inundation/flooding type irrigation system: In which
large quantities of water flowing in a river during floods
is allowed to inundate the land to be cultivated, thereby
saturating the soil.
 The excess water is then drained off and the land is
used for cultivation.
 It is also common in the areas near river deltas, where
the slope of the river and land is small.
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 Perennial irrigation system: In which irrigation water
is supplied according to the crop water requirement at
regular intervals, throughout the life cycle of the crop.
 The water for such irrigation may be obtained from
rivers or from wells.
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Some Important Terms for Irrigation
 Culturable Command Area (CCA): The gross command
area contains unfertile barren land, alkaline soil, local
ponds, villages and other areas as habitation. These
areas are called unculturable areas. The remaining area
on which crops can be grown satisfactorily is known as
cultivable command area (CCA).
Culturable command area can further be divided into 2
categories
 Culturable cultivated area: It is the area in which crop is grown at
a particular time or crop season.
 Culturable uncultivated area: It is the area in which crop is not
sown in a particular season.
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 Gross command area (GCA): The total area lying between
drainage boundaries which can be commanded or irrigated
by a canal system.
G.C.A = C.C.A + unculturable area
 Water Tanks: These are dug areas of lands for storing
excess rain water.
 Water logged area: An agricultural land is said to be
waterlogged when its productivity or fertility is affected by
high water table. Depth of water-table at which it tends to
make soil water-logged and harmful to growth and
subsistence of plant life depends upon height of capillary
fringe. The height of capillary fringe is more for fine
grained soil and less for coarse grained ones. 7/25/2014
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 Outlet: This is a small structure which admits water from
the distributing channel to a water course of field channel.
Thus an outlet is a sort of head regulator for the field
channel delivering water to the irrigation fields.
 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.
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Soil Water Plant Relationship
Vocabulary Terms
 Potable- drinkable, free from contaminants.
 Irrigation- addition of water to plants to supplement water
provided by rain or snow.
 Water Cycle – the cycling of water among the water sources
to surface, to atmosphere, back to surface.
 Precipitation – falling products of condensation in the
atmosphere, as rain, snow, or hail.
 Evaporation – to change from a liquid or solid state to a
vapor or gas.
 Saturate – this happens to soil when water is added until all
the spaces or pores are filled.
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Gravitational Water
Super Fluous Water
Easily Available
Water
Wilting Limit
Oven Dried Soil
Water Available
With Difficulty
Field Capacity
Wilting Coefficient
Ultimate Wilting
Hygroscopic Water
Water Not
Available
Available Water/
Capillary Water
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Types of Groundwater
 Gravitational – also called “free water.” - This is the
water that drains out of the soil after it has been
wetted.
 This water moves downward through the soil
because of the pull of gravity.
 This water also feeds wells and springs.
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 Capillary – water that moves into and is held in the
soil by capillary forces (or pertaining to the
attraction or repulsion between a solid and a liquid).
 Plant roots can absorb or take up this moisture.
 The size of the soil pore will influence the amount of
water held by capillary forces. - Provides most of the
moisture for plant growth.
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 Hygroscopic - very thin water films around the soil
particles.
 These films are held by extremely strong forces that
cause the water molecules to be arranged in a semi-
solid form.
 This water is unavailable to plants.
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How is Soil Water Classified?
 Hygroscopic Water is held so strongly by the soil
particles (adhesion), that it is not available to the
plants.
 Capillary Water is held by cohesive forces greater
than gravity and is available to plants.
 Gravitational Water is that water which cannot be
held against gravity. As water is pulled down through
the soil, nutrients are "leached" out of the soil
(nitrogen)
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Levels of Water in Soil
 Saturation Point – the moisture point at which all of
the pore spaces are filled with water.
 Occurs when an area receives a lot of rain on a daily
basis and the water does not get absorbed by plants,
evaporation is at a low do to the lack of sunlight, and
runoff areas (ditches, drains) are to capacity.
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 Field Capacity – the maximum amount of water left
in the soil after losses of water to the forces of gravity
have ceased and before surface evaporation begins.
 Occurs when the soil contains the maximum amount
of capillary water.
100
SampleSoilDriedtheofWeight
SoilofVolumeCertainainRetainedWaterofWeight
CapacityField 








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 Wilting Point – the point at which the plant can no
longer obtain sufficient water from the soil to meet
its transpiration needs.
 At this point the plant enters permanent wilt and
dies.
 Available Soil Water – that amount present in a soil
which can be moved by plants.
 It is designated as the difference between the field
capacity and the wilting point.
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The Hydrolic
(Water) Cycle
 Water is constantly
moving through the
atmosphere and
into and out of the
soil.
 Soil moisture is one
portion of the cycle
which can be
controlled to the
greatest extent by
affecting the soil.
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How Does Water Enter the Soil?
 through pores in the soil
 sandy soils have the largest pores, but are often filled
with other material
 medium textured soils (loamy) have good water
entry properties
 clays, pores swell shut when they get wet
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 Water Holding Capacity – is a soil property which
represents the amount of water a soil can retain after
it has been saturated by rain and downward
movement has ceased.
 Transpiration – the process by which water, as a
vapor, is lost by living plants.
 Translocation – the process by which water moves
through a plant from the roots to the leaves.
 Wilting Point – the moisture content of a soil in
which growing plants wilt and will not recover after
water is added.
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 Evapotranspiration - the combination of water that
is lost from the soil through evaporation and through
transpiration from plants as a part of their metabolic
processes
 Adhesion – the attraction of two different molecules
(water to soil)
 Cohesion – the attraction of two similar molecules
(water to water)
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Depth of Soil Water Available to Plants
dw
d
The depth of water stored in the root zone of
soil may be determined as follows:
Let, d = depth of root zone
d = unit weight of dry soil
w = unit weight of water
Unit weight of soil = (1 x d) x d
Unit weight of water = (1 x dw) x w
100
SampleSoilDriedtheofWeight
SoilofVolumeCertainainRetainedWaterofWeight
CapacityField  





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 
 d
d
CF
d
ww



1
1
..


CapacityField dd
w
d
w


CapacityFieldcapacity,fieldat  dSdw
Depth of water held by soil at permanent wilting point
PointWiltingPermanent dS
PWP)-(F.C.WaterAvailableofDepth  dS
PWP)-(F.C.75.0soilofrWater/meteAvailableReadilyofDepth  S
If the water content of the soil at lower limit of the readily available
moisture is mo, the readily available depth of water is
 om-F.C. dS
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Water Holding Capacities of Soils
The amount of water a soil can retain is influenced by:
 soil texture
 soil structure
 organic matter.
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Soil Texture
 The smaller the soil particles, the greater the soil’s
water holding capacity. Clay has more water holding
capacity than sand.
 Small soil particles (clay) have more small pores or
capillary spaces, so they have a higher water holding
capacity. Large soil particles (sand) have fewer
capillary spaces, therefore less ability to hold water.
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Soil Structure
 A soil structure has a direct correlation to the
amount of water it can retain.
Organic Matter
 Organic matter aids in cementing particles of clay,
silt, and sand together into aggregates which
increases the water holding capacity.
 Decomposition of organic matter also adds vital
nutrients to the soil.
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Proportions of Soil Constituents
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Bulk Density (b)
b = soil bulk density, g/cm3 , Ms = mass of dry soil, g
Vb = volume of soil sample, cm3 , Typical values: 1.1 -
1.6 g/cm3
Particle Density (p)
p = soil particle density, g/cm3 , Ms = mass of dry soil,
g , Vs = volume of solids, cm3 , Typical values: 2.6 -
2.7 g/cm3
)/( 3
cmg
V
M
b
s
b 
)/( 3
cmg
V
M
s
s
p 
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Porosity ()
%1001
soilofvolume
poresofvolume










p
b



Typical values: 30 – 60%
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Soil Moisture Content
 The soil moisture content indicates the amount of
water present in the soil.
 It is commonly expressed as the amount of water (in
mm of water depth) present in a depth of one metre
of soil.
 For example: when an amount of water (in mm of
water depth) of 150 mm is present in a depth of one
metre of soil, the soil moisture content is 150 mm/m
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Water in Soils
 Soil water content
Mass water content (m)
m = mass water content (fraction)
Mw = mass of water evaporated, g (24 hours @ 105oC)
Ms = mass of dry soil, g
s
w
m
M
M

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Volumetric water content (v)
v = volumetric water content (fraction)
Vw = volume of water, Vb = volume of soil sample
At saturation, v = 
As = apparent soil specific gravity = b/ w (w = density
of water = 1 g/cm3)
As = b numerically when units of g/cm3 are used
b
w
v
V
V

msv A  
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Equivalent depth of water (d)
 d = volume of water per unit land area
d= (vA L)/A = vL
 d = equivalent depth of water in a soil layer
 L = depth (thickness) of the soil layer
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Volumetric Water Content & Equivalent Depth (d)
Wet Weight
of Soil, g
Dry Weight
of Soil,g
Volume of
Water,cc
Wet Soil
Sample
Dry Soil
Sample
Water
– =
Bulk
Volume, cc
Equivalent
Depth
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Volumetric Water Content & Equivalent Depth (d)
Typical Values for Agricultural Soils
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Water-Holding Capacity of Soil
Effect of Soil Texture
Dry Soil
Gravitational Water
Available Water
Unavailable Water
Water Holding Capacity
Silty Clay LoamCoarse Sand
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Soil Water Constants
 For a particular soil, certain soil water proportions are defined
which dictate whether the water is available or not for plant
growth which are called as soil water constants.
 Saturation capacity: This
is the total water content of the
soil when all the pores of the
soil are filled with water. It is
also termed as the maximum
water holding capacity of the
soil. At saturation capacity,
the soil moisture tension is
almost equal to zero.
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 Field capacity: this is water retained by an
initially saturated soil against force of gravity.
Hence, as gravitational water gets drained off
from soil, it is said to reach field capacity. At
field capacity, macro-pores of soil are drained
off, but water is retained in the micropores.
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Two stages of wilting points are recognized which are:
 Temporary Wilting Point: this denotes the soil water
content at which the plant wilts at day time, but recovers
during right or when water is added to the soil.
 Ultimate Wilting
Point: at such a soil
water content, the
plant wilts and fails
to regain life even
after addition of
water to soil.
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 Permanent Wilting
Point: plant roots are
able to extract water from
soil matrix, which is
saturated up to field
capacity. However, as
water extraction proceeds,
moisture content
diminishes and negative
pressure increases. At one
point, plant cannot extract
any further water and thus
wilts.
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It must be noted that the above water contents are expressed as
percentage of water held in the soil pores, compared to a fully
saturated soil.
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Soil at saturation capacity moisture content 100%
After draining out of gravitational
water, soil at field capacity
Gravitational water
Gravitational water
Capillary Water (Available Water)
After extraction of available water by
plants
After drying in oven moisture content 0%
Capillary Water (Available Water)
Hygroscopic water
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 Available Water
Water held in the soil between field capacity and
permanent wilting point i.e. “Available” for plant use
 Available Water Capacity (AWC)
AWC = fc - wp
Units: depth of available water per unit depth of soil,
“unitless” (in/in, or mm/mm)
Measured using field or laboratory methods
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 Soil Hydraulic Properties & Soil Texture
Values can vary considerably from these within each soil texture
Soil Texture fc wp AWC
in/in or m/m
Coarse Sand 0.10 0.05 0.05
Sand 0.15 0.07 0.08
Loamy Sand 0.18 0.07 0.11
Sandy Loam 0.20 0.08 0.12
Loam 0.25 0.10 0.15
Silt Loam 0.30 0.12 0.18
Silty Clay Loam 0.38 0.22 0.16
Clay Loam 0.40 0.25 0.15
Silty Clay 0.40 0.27 0.13
Clay 0.40 0.28 0.12
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 Fraction Available Water Depleted (fd)
(fc - v) = soil water deficit (SWD)
v = current soil volumetric water content
 Fraction Available Water Remaining (fr)
(v - wp) = soil water balance (SWB)











wpfc
vfc
df













wpfc
wpv
rf


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 Total Available Water (TAW)
TAW = (AWC) (Rd)
TAW = total available water capacity within the plant root zone,
(inches), AWC = available water capacity of the soil, (inches of
H2O/inch of soil), Rd = depth of the plant root zone, (inches)
If different soil layers have different AWC’s, need to sum up the
layer-by-layer TAW’s
TAW = (AWC1) (L1) + (AWC2) (L2) + . . . (AWCN) (LN)
L = thickness of soil layer, (inches) , 1, 2, N: subscripts represent
each successive soil layer
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 Depth of Penetration
Can be viewed as sequentially filling the soil profile in
layers
 Deep percolation: water penetrating deeper than the
bottom of the root zone
 Leaching: transport of chemicals from the root zone
due to deep percolation
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Water Requirements of Crops
 Depth of water applied during irrigation
 Duty of water and delta improvement of duty
 Command area and intensity of irrigation
 Consumptive use of water
 Evapotranspiration
 Irrigation efficiencies
 Assessment of irrigation water
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 The term water requirements of a crop means the
total quantity of all water and the way in which a
crop requires water, from the time it is sown to the
time it is harvested.
 The water requirement of crop varies with the crop
as well as with the place.
 The same crop may have different water
requirements at different places of the same country.
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Factors affecting Water Requirement
 Water table: high water table less requirement, vice
versa.
 Climate: In hot climate evaporation loss is more, hence
requirement more, vice versa.
 Ground slope: ground is steep, the water flows down very
quickly and soil gets little time to absorb, so requirement
more. If ground is flat less requirement.
 Intensity of irrigation: if intensity of irrigation for a
particular crop is high, then more area comes under the
irrigation system and requirement is more, vice versa.
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 Type of soil: sandy soil water percolates very quickly, so
requirement is more. Clay soil retention capacity is more,
so less requirement.
 Method of application of water: surface method more
water is required to meet up evaporation. In sub surface
and sprinkler method less water required.
 Method of ploughing: In deep ploughing less water
required, because soil can retain moisture for longer
period. In shallow ploughing more water required.
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Base
 Base is defined as the period from the first to the last
watering of the crop just before its maturity.
 Also known as base period.
 Denoted as “B” and expressed in no of days.
Crop Base in Days
Rice 120
Wheat 120
Maize 100
Cotton 200
Sugarcane 320
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Delta
 Each crop requires certain amount of water per hectare for
its maturity.
 If the total of amount of water supplied to the crop is stored
on the land without any loss, then there will be a thick of
water standing on the land.
 This depth of water layer is known as Delta for the crop.
 Donated by “Δ” expressed on cm.
Kharif Crop Delta in cm Rabi Crop Delta in cm
Rice 125 Wheat 40
Maize 45 Mustard 45
Groundnut 30 Gram 30
Millet 30 Potato 75
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Delta
if a crop requires 10 waterings at an interval of 20 days
with each watering of depth 12.5 cm then delta
= 10 * 12.5 = 125 cm and base period can be
calculated as
B = 10 * 20 = 200 days
 
in hectaregrowingiscropwhichonlandofArea
metre-in hectarerequiredwaterofquanityTotal
Delta
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Duty
Duty of water is defined as no of hectares that can be irrigated
by constant supply of water at the rate of one cumec throughout
the base period.
Denoted as “D” and expressed in hectares/cumec.
Varies with soil condition, method of ploughing, method of
application of water.
1 cumec-day = 1 m3/sec for one day.
Crop Duty in hectares/cumec
Rice 900
Wheat 1800
Cotton 1400
Sugarcane 800
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Method of Expressing Duty
Number of hectares /cumec of water can irrigate during base period
eg. 1000hectares/cumec
Total depth of water
Number of hectares /million cubic metre of stored water (for tank
irrigation)
Types of Duty
Gross Duty: duty of water measured at head of main canal.
Nominal Duty: duty sanctioned as per schedule of irrigation dept.
Economic Water Duty: duty of water which results in maximum crop
yield
Designated Duty: duty of water assumed in an irrigation project for
design of canals.
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Factors affecting Duty
 Soil characteristics: if soil of the canal bed is porous
and coarse grained, it leads to more seepage loss and
low duty. If soil is compact and close grained,
seepage loss will less and high duty.
 Climatic condition: when atmospheric temp. of
command area becomes high, the evaporation loss is
more and duty becomes low and vice versa.
 Rainfall: if rainfall is sufficient during crop period,
less quantity of irrigation water shall be required and
duty will more and vice versa.
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 Base period: when base period is longer, the water
requirement will be more and duty will low and vice
versa.
 Type of crop: water requirement of various crops are
different. So the duty also varies.
 Topography of agricultural land: if land has slight
slope duty will high as water requirement optimum.
As slope increases duty increases because there is
wastage of water.
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 Method of ploughing: deep ploughing by tractor
requires less quantity of water, duty is high. Shallow
ploughing by bullocks requires more quantity of
water, duty is low.
 Methods of irrigation: duty is high in case of
perennial irrigation system as compared to
inundation irrigation system. Because in perennial
system head regulator is used.
 Water tax: if some tax is imposed on the basis of
volume of water consumption, the farmer will use
the water economically, duty will be high.
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Methods of improving duty
 Proper ploughing: Ploughing should be done
properly and deeply, so that moisture retaining
capacity of soil is increased.
 Methods of supplying water: this should be decided
according to the field and soil conditions.
 Furrow method – crops shown in row
 Contour method – hilly area
 Basin method – for orchards
 Flooding method – plain lands
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 Canal lining: to reduce percolation loss the canals
should be lined according to site condition.
 Transmission loss: to reduce this canals should be
taken close to the irrigable land as far as possible.
 Crop rotation: crop rotation should be adopted to
increase the moisture retaining capacity and fertility
of the soil.
 Implementation of tax: the water tax should be
imposed on the basis of volume of water
consumption.
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Total Quantity of Water Required (WR)
= consumptive use (A) + conveyance losses (B) +
special needs (C)
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Depth of Water Applied during Irrigation (dw)
Where d = depth of root zone, F.C. = field capacity,
mo = lower limit of readily available moisture content
 o
w
d
w mCFdd  ..


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If Cu is rate of daily consumptive
use, frequency of irrigation is
days)(in
u
w
w
C
d
f 
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seconds)(in
q
dA
t w

Irrigation Time Required
The frequency once decided need to be applied in the form of water
with the time of supply being given also of equal importance otherwise
sacrificing the planning of irrigation on the whole
t = time required to pump water
dw = depth of water to be applied in m
mo = required moisture content to bring soil moisture at FC
A = area to be irrigated in sq. m.
q = discharge in cumecs
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Relation between Base, Delta and Duty
Let, D = duty of water in hectare/cumec, B = base in
days, Δ = delta in m
From definition, one cumec of water flowing
continuously for “B” days gives a depth of water Δ
over an area “D” hectares. i.e.
1 cumec for 1 days gives Δ over D/B hectares.
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or 1 cumec for B days gives Δ over D/B hectares.
or 1 cumec for 1 day = (D/B) × Δ hectare – meter
1 cumec- day = (D/B) × Δ hectare – meter ----- (i)
Again, 1 cumec- day = 1 × 24 × 60 × 60 = 86400 m3 =
8.64 hectare – meter ------- (ii)
(1 hectare = 10, 000 m2)
From (i) & (ii) = (D/B) × Δ = 8.64
Δ = (8.64 × B)/ D = in m
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Command Area
"The area which lies on down stream side of project to
which water can reach by gravity action."
There are the three types of commanded areas.
 Gross Commanded Area (G.C.A): The Gross
commanded area is the total area lying between
drainage boundaries which can be irrigated by a
canal system.
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 Cultivable Commanded Area (C.C.A): It is the net
area, which can be irrigated by a canal system. It
includes all land on which cultivation is possible,
though all area may not be under cultivation at the
time.
G.C.A. = C.C.A. + Uncultivable area
 Irrigable Commanded Area (I.C.A): It is the part of
cultivable commanded area, which can be irrigated.
All the C.C.A. cannot be irrigated because of high
elevation.
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Intensity of Irrigation
 It is the ratio of area irrigated per season to total
irrigable areas or small projects is based on this.
Crop Period
 It is the time in days, that a crop takes from the
instant of its sowing to that of its harvesting.
Rabi Crops
 Crops sown in autumn (October) and harvested in
spring (March). Eg. Wheat, Coriander, Fenugreek,
Mustard, Chick Pea, Potato, Oats
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Kharif Crops
 Crops sown in beginning of southwest monsoon and
harvested in autumn. Eg. Cotton, juwar, seaseme,
castor, soyabean
Kor Watering, Depth & Period
 The first watering after the plants have grown few
centimeters high is known as kor watering, the depth
of water applied as kor depth and the portion of the
base period in which it is required is kor period.
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Paleo
 Defined as the first watering before sowing of any
crop to make the soil ready for sowing.
Intensity of Irrigation
 Defined as the percentage of culturable commanded
area proposed to be irrigated during a year.
Crop Ratio
 Ratio of area of land irrigated during rabi and kharif
also known as rabi – kharif ratio.
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Time Factor
 Ratio of number of days canal run to number of days
of irrigation period.
Outlet Factor
 Defined as the duty at the outlet < duty at field
considering transmission losses.
Capacity Factor
 Ratio of mean supply to full supply of canal.
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Types of Soil
 Alluvial soil: formed by deposition of silt carried by river
water during flood. Silt is formed due to weathering action
of rocks by heavy current of river water in the hilly regions.
Found in Indo –Gangetic plains, Brahmaputra plains.
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 Black soil: originated by weathering action on rocks like
granite, basalt etc. Mainly found in AP, MP, TN, Gujarat.
They are sticky when wet and very hard when dry. Suitable
for cultivation of cotton.
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 Red soil: formed by weathering
action of rocks of igneous and
metamorphic group. Water
absorbing capacity very low.
Found in Karnataka, TN, Orissa,
WB, Maharashtra etc.
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 Laterite soil: formed by
weathering action of laterite
rocks. Yellowish red in color and
having good drainage property.
Found in Kerala, Karnataka,
Orissa, Assam etc.
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Consumptive Use of Water
 It is defined as total quantity of water used for the
growth of plants by transpiration and the amount of
lost by evaporation.
 It is also known as evapo-transpiration.
 Expressed in hectare-meter or as depth of water in
m.
 The value of consumptive use of water is vary from
crop to crop, time to time, place to place.
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Evapotranspiration
a) Evaporation: The process by which water is changed from
the liquid or solid state into the gaseous state through the
transfer of heat energy.
b) Transpiration: The evaporation of water absorbed by the
crop which is used directly in the building of plant tissue in a
specified time. It does not include soil evaporation.
c) Evapotranspiration, ET: It is the sum of the amount of water
transpired by plants during the growth process and that
amount that is evaporated from soil and vegetation in the
domain occupied by the growing crop. ET is normally
expressed in mm/day.
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Factors that affect Evapotranspiration
 Weather parameters
 Crop Characteristics
 Management and Environmental aspects are factors
affecting ET
Weather Parameters: The principal weather conditions
affecting Evapotranspiration are:
 Radiation
 Air temperature
 Humidity and
 Wind speed.
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Crop Characteristics that affect ET :
 Crop Type
 Variety of Crop
 Development Stage
 Crop Height
 Crop Roughness
 Ground Cover
 Crop Rooting Depth
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Management and Environmental Factors :
 Factors such as soil salinity,
 Poor land fertility,
 Limited application of fertilizers,
 Absence of control of diseases and
 Pests and poor soil management
 May limit the crop development and reduce soil
Evapotranspiration.
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 Other factors that affect ET are ground cover, plant
density and soil water content.
 The effect of soil water content on ET is conditioned
primarily by the magnitude of the water deficit and
the type of soil.
 Too much water will result in water logging which
might damage the root and limit root water uptake
by inhibiting respiration.
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Determination of ET
 Evapotranspiration is not easy to measure.
 Specific devices and accurate measurements of various
physical parameters or the soil water balance in
lysimeters are required to determine ET.
 The methods are expensive, demanding and used for
research purposes.
 They remain important for evaluating ET estimates
obtained by more indirect methods.
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Water Balance Method
 Water Balance or Budget Method is a measurement of
continuity of flow of water. It consists of drawing up a
balance sheet of all the water entering and leaving a
particular catchment or drainage basin. The water balance
equation can be written as:
ET = I + P – RO – DP + CR + SF + SW
Where: I is Irrigation, P is rainfall, RO is surface runoff, DP
is deep percolation, CR is capillary rise, SF and SW are
change in sub-surface flow and change in soil water content
respectively
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Lysimeter Method
 A water tight tank of cylindrical shape having dia about 2 m
and depth about 3 m is placed vertically in ground. The
tank is filled with sample soil. Bottom of the tank consists
of sand layer and a pan for collecting surplus water. The
consumptive use of water is measured by the amount of
water required for the satisfactory growth of plants with in
tank.
Cu = Wa – Wd
(Cu = consumptive use, Wa = water applied, Wd = Water
drained off)
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Simplified Pathway of Water in an Evapotranspiration
Measuring Apparatus
GRASS
SOIL
Water Added (A) Rainfall (R)Evaporation (PE)
Percolated Water (P)
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Field Experimental Method
 Some fields are selected for expt.
 The quantity of water is applied in such a way that it
is sufficient for satisfactory growth of crops.
 There should be no percolation or deep runoff.
 If there is any runoff it should be measured and
deducted from the total quantity of water applied.
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Soil Moisture Study
 Several plots of land are selected where irrigation water is to be
supplied. The soil samples are taken from diff depths at the root
zone of the plants before and after irrigation.
 Water contents of soil samples are determined by laboratory tests.
 Depth of water removed from soil determined by
Dr= depth of water removed in m, p = % of water content, w = Sp.
Gr. of soil, d= depth of soil in m)
 Total quantity of water removed in 30 days period is calculated.
 Then a curve of water consumption versus time is prepared which
is used to calculate the water consumption for any period.
100
dwp
Dr


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Dr. L. S. Thakur

Irrigation Efficiencies
 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 is lost in irrigation during various processes and,
therefore, there are different kinds of irrigation
efficiencies.
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Efficiency of Irrigation
InputWater
OutputWater
soiltoappliedwatertotalofAmount
soilinstoredwaterofAmount
IrrigationofEfficiency 
Cumec - day
 Quantity of water flowing at 1 m3/s in one day.
Hectare - metre
 Total quantity of water required to fill 1 hectare area with
1 metre depth.
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Overlap Allowance
 Defined as extra quantity of water required to show
irrigation for crop overlapping requirements. This
percentage is 5 to 10.
100 sq. mt. = 1 are 100 are = 1 hectare
1 hectare = 10000 sq. metre 1 acre = 0.4047 hectare
1 cusec = 0.0283 cumec 1 cumec = 1 m3/sec
1 cumec – day = 8.64 hectare
- metre
1 cumec – day = 86400 cubic
metre
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Efficiency of Water-conveyance (ηc)
 It is the ratio of amount of water applied to the land
to the amount of water supplied from the reservoir.
 It may be represented by ηc.
where, ηc = Water conveyance efficiency, Wl = amount
of water applied to land, and Wr = Water supplied
from reservoir.
100








r
l
c
W
W

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Water Application Efficiency (ηa)
 Ratio of water stored in root zone of plants to the
water applied to the land.
where, ηa = water application efficiency, Wz = amount
of water stored in root zone, Wl = amount of water
applied to land
100
l
z
a
W
W

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Water Use Efficiency (ηu)
 Ratio of the amount of water used to the amount of
water applied. Denoted by ηu .
where, ηu = water efficiency use, Wu = water used, Wl =
water applied
100
l
u
u
W
W

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Consumptive Use Efficiency (ηcu )
 Ratio of the consumptive use of water to the amount
of water depleted from the root zone.
where, ηcu = consumptive use efficiency, Cu =
consumptive use of water, Wp = amount of water
depleted from root zone
100
p
u
cu
W
C

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Standard of Irrigation water
Constituent Long Term Use (mg/L) Short Term Use (mg/L)
Aluminium 5.0 20.0
Arsenic 0.10 2.0
Beryllium 0.10 0.5
Boron 0.75 2.0
Chromium 0.1 2.0
Cobalt 0.05 5.0
Copper 0.2 5.0
Fluoride 1.0 15.0
Iron 5.0 20.0
Lead 5.0 10.0
Manganese 0.2 10.0
Nickel 0.2 20.0
Zinc 0.2 10.0
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Measurement of Consumptive
Use of Water
Direct Measurement
Methods
Tank and Lysimeter
Method
Field
Experimental
Plots
Soil Moisture
Studies
Integration
Methods
Inflow & Outflow
Studies for Large Areas
Use of Empirical
Formula
Penman
Method
Jensen –
Haise method
Blaney –
Criddle Method
Hargreaves
Method
Thornthwaite
Method
Hargreaves Class A Pan
Evaporation Method
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Methods of Measuring Irrigation Water
a) Direct method: Collect water in a contained of known
volume e.g. bucket. Measure the time required for water
from an irrigation source e.g. siphon to fill the bucket.
Flow rate = Volume/time m3/hr or L/s etc.
Weirs: Weirs are regular notches over which water flows.
They are used to regulate floods through rivers, overflow
dams and open channels. Weirs can be sharp or broad
crested; made from concrete timber, or metal and can be of
cross-section rectangular, trapezoidal or triangular. Sharp
crested rectangular or triangular sections are commonly
used on the farm.
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The discharge through a weir is usually expressed as:
Q = C L Hm
where Q is the discharge, C is the coefficient dependent on
the nature of weir crest and approach conditions, L is the
length of crest, H is the head on the crest and m is an
exponent depending on weir opening.
Weirs should be calibrated to determine these parameters
before use eg. for trapezoidal weirs(Cipoletti weir),
Q = 0.0186 L H1.5
Q is discharge in L/s, L, H are in cm
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The discharge through a weir is usually expressed as:
Q = C x L x H x m
where Q is the discharge, C is the coefficient dependent on the
nature of weir crest and approach conditions, L is the length of
crest, H is the head on the crest and m is an exponent depending
on weir opening.
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Weirs should be
calibrated to
determine these
parameters before
use eg. for
trapezoidal
weirs(Cipoletti
weir),
Q = 0.0186 L H1.5
where, Q is discharge
in L/s, L, H are in
cm.
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Orifices: An orifice is an opening
in the wall of a tank containing
water. The orifice can be
circular, rectangular, triangular
or any other shape. The
discharge through an orifice is
given by:
Q = C A 2 g h
Where Q is the discharge rate; C is
the coefficient of discharge (0.6
- 0.8); A is the area of the
orifice; g is the acceleration due
to gravity and h is the head of
water over an orifice.
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Flumes: Hydraulic flumes are artificial open channels or sections
of natural channels. Two major types of hydraulic flumes are
Parshall or Trapezoidal ones. Flumes need to be calibrated after
construction before use.
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Dr. L. S. Thakur

For streams, use gauging. A current meter is used to measure
velocity at 0.2 and 0.8 Depth or at only 0.6 depth. Measure areas
of all sections using trapezoidal areas.
Q = ai x vi
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Using Floats: A floating object is put in water and observe the
time it takes the float e.g. a cork to go from one marked area to
another. Assuming the float travels D meters in t secs
 Velocity of water at surface = ( D/t ) m/s
 Average velocity of flow = 0.8 (D/t)
 Flow rate, Q = Cross sectional area of flow x velocity.
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Dr. L. S. Thakur

b) Integration Method: total area of interest divided into
sub plots as per crop growing or subdivided under crop, natural
vegetation, water ponds, bare land. The consumptive use then
calculated as sum of all according to requirement of each.
Where, dw1 = consumptive uses of water for crop, dw2 =
consumptive use of water for natural vegetation, dw3 =
evaporation from the water surface, dw4 = evaporation from
barren land.
Once the value is obtained it can be expressed in terms of depth of
water by dividing by the total area.
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Dr. L. S. Thakur

c) Inflow & Outflow Studies: found for the total area
using the expression
Where, U = consumptive use of water in hect-m, I = total
inflow during 12 months, P = yearly precipitation on area,
Gs = Ground water storage of area at beginning of year, Ge
= Ground water storage of area at end of year, R = yearly
outflow of the area. All values in hect – m.
    RGGPIU es 
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Dr. L. S. Thakur

Irrigation engineering module 1

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