irrigation engineering module 1

80% human body made

up of water.

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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 . ThakurC 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 o m

Irrigation EngineeringModule 1

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Outline

Necessity of irrigationScope of irrigation engineeringBenefits and ill effects of irrigationIrrigation development in IndiaTypes of irrigation systemsSoil-water plant relationship: Classification of soil

water- soil moisture contents- depth of soil water availableto plants-permanent and ultimate wilting point

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What is Irrigation Engineering

Irrigation is the artificial application of water to thesoil for the purpose of supplying the moistureessential for plant growth

It is used to assist in growth of agricultural crops,maintenance of landscapes, and revegetation ofdisturbed soils in dry areas and during periods ofinadequate rainfall.

Irrigation is often studied with drainage, i.e. thenatural 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 fromMesopotamia barely yields were 2500L/ha, now only¼ 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 waterthrough transforming it into water vapor (where it is “lost”to the atmosphere), letting it seep into ground, orsignificantly 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, Recreationmay involve using water as a medium (example: swimming)and/or extracting energy from water (examples: white-water rafting, surfing), Transportation is especiallyimportant 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 likeIndia, irrigation has played a major role in theproduction process. There is evidence of the practiceof irrigation since the establishment of settledagriculture during the Indus Valley Civilization(2500 BC).

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These irrigation technologies were in the form ofsmall and minor works, which could be operated bysmall households to irrigate small patches of landand did not require co-operative effort.

In the south, perennial irrigation may have begunwith construction of the Grand Anicut by the Cholasas early as second century to provide irrigation fromthe Cauvery river.

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At beginning of 19th century, there was large no ofwater tanks in peninsular India and several canals innorthern India were build.

The upper Ganga canal, upper Bari Doab canal andthe Krishna and Godavari delta system wereconstructed between 1836-1866.

During the last fifty years, gross irrigated area (GIA)of India has increased more than three fold from 22to 76 million Hectares.

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Groundwater irrigation in India developed duringthe period of green revolution and contributed muchin 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 inthe year 1987 which was revised in 2002.

The policy document lays down the fact thatplanning and development of water resources shouldbe governed by the national perspective.

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Aspects Related to Irrigation from Policy

Irrigation planning either in an individual project or in awatershed as a whole should take into account irrigability ofland, cost-effective irrigation options possible from allavailable sources of water and appropriate irrigationtechniques for optimizing water use efficiency.

close integration of water use and land use policies.

Water allocation in an irrigation system should be done withdue regard to equity and social justice.

Concerted efforts should be made to ensure that theirrigation potential created is fully utilised.

Irrigation being the largest consumer of fresh water, the aimshould 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 agriculturalland

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 hencewater is lifted up by pumps or by other mechanicaldevices for lifting water and conveyed to the agriculturalland 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 floodsis allowed to inundate the land to be cultivated, therebysaturating the soil.

The excess water is then drained off and the land isused for cultivation.

It is also common in the areas near river deltas, wherethe 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 atregular intervals, throughout the life cycle of the crop.

The water for such irrigation may be obtained fromrivers or from wells.

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Some Important Terms for Irrigation

Culturable Command Area (CCA): The gross commandarea contains unfertile barren land, alkaline soil, localponds, villages and other areas as habitation. Theseareas are called unculturable areas. The remaining areaon which crops can be grown satisfactorily is known ascultivable command area (CCA).

Culturable command area can further be divided into 2categories

Culturable cultivated area: It is the area in which crop is grown ata 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 bewaterlogged when its productivity or fertility is affected byhigh water table. Depth of water-table at which it tends tomake soil water-logged and harmful to growth andsubsistence of plant life depends upon height of capillaryfringe. The height of capillary fringe is more for finegrained soil and less for coarse grained ones.

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Outlet: This is a small structure which admits water fromthe distributing channel to a water course of field channel.Thus an outlet is a sort of head regulator for the fieldchannel delivering water to the irrigation fields.

Permanent wilting point: or the wilting coefficient is thatwater content at which plants can no longer extractsufficient 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 WaterSuper 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 thewater that drains out of the soil after it has beenwetted.

This water moves downward through the soilbecause 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 thesoil by capillary forces (or pertaining to theattraction 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 ofwater held by capillary forces. - Provides most of themoisture 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 soilparticles (adhesion), that it is not available to theplants.

Capillary Water is held by cohesive forces greaterthan gravity and is available to plants.

Gravitational Water is that water which cannot beheld against gravity. As water is pulled down throughthe 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 dailybasis and the water does not get absorbed by plants,evaporation is at a low do to the lack of sunlight, andrunoff 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.

100Sample SoilDried the ofWeight

Soil of VolumeCertain a in Retained Water ofWeight CapacityField

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Wilting Point – the point at which the plant can nolonger obtain sufficient water from the soil to meetits transpiration needs.

At this point the plant enters permanent wilt anddies.

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 constantlymoving through theatmosphere andinto and out of thesoil.

Soil moisture is oneportion of the cyclewhich can becontrolled to thegreatest extent byaffecting 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 whichrepresents the amount of water a soil can retain afterit has been saturated by rain and downwardmovement has ceased.

Transpiration – the process by which water, as avapor, is lost by living plants.

Translocation – the process by which water movesthrough a plant from the roots to the leaves.

Wilting Point – the moisture content of a soil inwhich growing plants wilt and will not recover afterwater is added.

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Evapotranspiration - the combination of water thatis lost from the soil through evaporation and throughtranspiration from plants as a part of their metabolicprocesses

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

Sample SoilDried the ofWeight

Soil of VolumeCertain a in Retained Water ofWeight CapacityField

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d

dCF

d

ww

1

1..

CapacityField dd

w

dw

CapacityField capacity,field at dSdw

Depth of water held by soil at permanent wilting point

PointWiltingPermanent dS

PWP)- (F.C.Water Available of Depth dS

PWP)- (F.C.75.0soil of rWater/mete Available Readily of Depth 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’swater holding capacity. Clay has more water holdingcapacity than sand.

Small soil particles (clay) have more small pores orcapillary spaces, so they have a higher water holdingcapacity. Large soil particles (sand) have fewercapillary spaces, therefore less ability to hold water.

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Soil Structure

A soil structure has a direct correlation to theamount of water it can retain.

Organic Matter

Organic matter aids in cementing particles of clay,silt, and sand together into aggregates whichincreases the water holding capacity.

Decomposition of organic matter also adds vitalnutrients 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

)/( 3cmgV

M

b

sb

)/( 3cmgV

M

s

sp

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Porosity ()

%1001soil of volume

poresof volume

p

b

Typical values: 30 – 60%

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Soil Moisture Content

The soil moisture content indicates the amount ofwater present in the soil.

It is commonly expressed as the amount of water (inmm of water depth) present in a depth of one metreof soil.

For example: when an amount of water (in mm ofwater depth) of 150 mm is present in a depth of onemetre 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

wm

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

wv

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 definedwhich dictate whether the water is available or not for plantgrowth which are called as soil water constants.

Saturation capacity: This

is the total water content of thesoil when all the pores of thesoil are filled with water. It isalso termed as the maximumwater holding capacity of thesoil. At saturation capacity,the soil moisture tension isalmost 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 offfrom soil, it is said to reach field capacity. Atfield capacity, macro-pores of soil are drainedoff, 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 recoversduring right or when water is added to the soil.

Ultimate Wilting

Point: at such a soil

water content, theplant wilts and failsto regain life evenafter addition ofwater to soil.

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Permanent WiltingPoint: plant roots are

able to extract water fromsoil matrix, which issaturated up to fieldcapacity. However, aswater extraction proceeds,moisture contentdiminishes and negativepressure increases. At onepoint, plant cannot extractany further water and thuswilts.

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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 TextureValues 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 ofH2O/inch of soil), Rd = depth of the plant root zone, (inches)

If different soil layers have different AWC’s, need to sum up thelayer-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 thetotal quantity of all water and the way in which acrop requires water, from the time it is sown to thetime it is harvested.

The water requirement of crop varies with the cropas well as with the place.

The same crop may have different waterrequirements at different places of the same country.

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Factors affecting Water Requirement

Water table: high water table less requirement, viceversa.

Climate: In hot climate evaporation loss is more, hencerequirement more, vice versa.

Ground slope: ground is steep, the water flows down veryquickly and soil gets little time to absorb, so requirementmore. If ground is flat less requirement.

Intensity of irrigation: if intensity of irrigation for aparticular crop is high, then more area comes under theirrigation system and requirement is more, vice versa.

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Type of soil: sandy soil water percolates very quickly, sorequirement is more. Clay soil retention capacity is more,so less requirement.

Method of application of water: surface method morewater is required to meet up evaporation. In sub surfaceand sprinkler method less water required.

Method of ploughing: In deep ploughing less waterrequired, because soil can retain moisture for longerperiod. 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 ofwater 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 dayswith each watering of depth 12.5 cm then delta

= 10 * 12.5 = 125 cm and base period can becalculated as

B = 10 * 20 = 200 days

in hectare growing is crop whichon land ofArea

metre-in hectare required water of quanity TotalDelta

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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 DutyNumber of hectares /cumec of water can irrigate during base periodeg. 1000hectares/cumecTotal depth of waterNumber of hectares /million cubic metre of stored water (for tankirrigation)

Types of DutyGross 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 cropyieldDesignated Duty: duty of water assumed in an irrigation project fordesign of canals.

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Factors affecting Duty

Soil characteristics: if soil of the canal bed is porousand coarse grained, it leads to more seepage loss andlow duty. If soil is compact and close grained,seepage loss will less and high duty.

Climatic condition: when atmospheric temp. ofcommand area becomes high, the evaporation loss ismore and duty becomes low and vice versa.

Rainfall: if rainfall is sufficient during crop period,less quantity of irrigation water shall be required andduty 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 tractorrequires less quantity of water, duty is high. Shallowploughing by bullocks requires more quantity ofwater, duty is low.

Methods of irrigation: duty is high in case ofperennial irrigation system as compared toinundation irrigation system. Because in perennialsystem head regulator is used.

Water tax: if some tax is imposed on the basis ofvolume of water consumption, the farmer will usethe 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 canalsshould be lined according to site condition.

Transmission loss: to reduce this canals should betaken close to the irrigable land as far as possible.

Crop rotation: crop rotation should be adopted toincrease the moisture retaining capacity and fertilityof the soil.

Implementation of tax: the water tax should beimposed on the basis of volume of waterconsumption.

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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

dw mCFdd ..

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If Cu is rate of daily consumptive use, frequency of irrigation is

days)(in u

ww

C

df

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seconds)(in q

dAt w

Irrigation Time RequiredThe 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 indays, Δ = delta in m

From definition, one cumec of water flowingcontinuously for “B” days gives a depth of water Δover 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 towhich water can reach by gravity action."

There are the three types of commanded areas.

Gross Commanded Area (G.C.A): The Grosscommanded area is the total area lying betweendrainage boundaries which can be irrigated by acanal system.

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Cultivable Commanded Area (C.C.A): It is the netarea, which can be irrigated by a canal system. Itincludes all land on which cultivation is possible,though all area may not be under cultivation at thetime.

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 totalirrigable areas or small projects is based on this.

Crop Period

It is the time in days, that a crop takes from theinstant of its sowing to that of its harvesting.

Rabi Crops

Crops sown in autumn (October) and harvested inspring (March). Eg. Wheat, Coriander, Fenugreek,Mustard, Chick Pea, Potato, Oats

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Kharif Crops

Crops sown in beginning of southwest monsoon andharvested in autumn. Eg. Cotton, juwar, seaseme,castor, soyabean

Kor Watering, Depth & Period

The first watering after the plants have grown fewcentimeters high is known as kor watering, the depthof water applied as kor depth and the portion of thebase period in which it is required is kor period.

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Paleo

Defined as the first watering before sowing of anycrop to make the soil ready for sowing.

Intensity of Irrigation

Defined as the percentage of culturable commandedarea proposed to be irrigated during a year.

Crop Ratio

Ratio of area of land irrigated during rabi and kharifalso known as rabi – kharif ratio.

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Time Factor

Ratio of number of days canal run to number of daysof irrigation period.

Outlet Factor

Defined as the duty at the outlet < duty at fieldconsidering 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 actionof 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. Suitablefor cultivation of cotton.

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Red soil: formed by weathering

action of rocks of igneous andmetamorphic group. Waterabsorbing capacity very low.Found in Karnataka, TN, Orissa,WB, Maharashtra etc.

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Laterite soil: formed by

weathering action of lateriterocks. Yellowish red in color andhaving 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 thegrowth of plants by transpiration and the amount oflost by evaporation.

It is also known as evapo-transpiration.

Expressed in hectare-meter or as depth of water inm.

The value of consumptive use of water is vary fromcrop 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 thetransfer of heat energy.

b) Transpiration: The evaporation of water absorbed by the

crop which is used directly in the building of plant tissue in aspecified 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 thatamount that is evaporated from soil and vegetation in thedomain occupied by the growing crop. ET is normallyexpressed 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, plantdensity and soil water content.

The effect of soil water content on ET is conditionedprimarily by the magnitude of the water deficit andthe type of soil.

Too much water will result in water logging whichmight damage the root and limit root water uptakeby inhibiting respiration.

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Determination of ET

Evapotranspiration is not easy to measure.

Specific devices and accurate measurements of variousphysical parameters or the soil water balance inlysimeters are required to determine ET.

The methods are expensive, demanding and used forresearch purposes.

They remain important for evaluating ET estimatesobtained 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 abalance sheet of all the water entering and leaving aparticular catchment or drainage basin. The water balanceequation can be written as:

ET = I + P – RO – DP + CR + SF + SW

Where: I is Irrigation, P is rainfall, RO is surface runoff, DPis deep percolation, CR is capillary rise, SF and SW arechange in sub-surface flow and change in soil water contentrespectively

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Lysimeter Method

A water tight tank of cylindrical shape having dia about 2 mand depth about 3 m is placed vertically in ground. Thetank is filled with sample soil. Bottom of the tank consistsof sand layer and a pan for collecting surplus water. Theconsumptive use of water is measured by the amount ofwater required for the satisfactory growth of plants with intank.

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 rootzone 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

dwpDr

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Irrigation Efficiencies

Efficiency is the ratio of the water output to the waterinput, and is usually expressed as percentage.

Input minus output is nothing but losses, and hence, iflosses are more, output is less and, therefore, efficiencyis less.

Hence, efficiency is inversely proportional to the losses.

Water is lost in irrigation during various processes and,therefore, there are different kinds of irrigationefficiencies.

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Efficiency of Irrigation

Input Water

Output Water

soil toapplied water total ofAmount

soilin stored water ofAmount Irrigation of Efficiency

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 showirrigation for crop overlapping requirements. Thispercentage 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 landto the amount of water supplied from the reservoir.

It may be represented by ηc.

where, ηc = Water conveyance efficiency, Wl = amountof water applied to land, and Wr = Water suppliedfrom reservoir.

100

r

lc

W

W

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Water Application Efficiency (ηa)

Ratio of water stored in root zone of plants to thewater applied to the land.

where, ηa = water application efficiency, Wz = amountof water stored in root zone, Wl = amount of waterapplied to land

100l

za

W

W

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Water Use Efficiency (ηu)

Ratio of the amount of water used to the amount ofwater applied. Denoted by ηu .

where, ηu = water efficiency use, Wu = water used, Wl = water applied

100l

uu

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 waterdepleted from root zone

100p

ucu

W

C

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Standard of Irrigation waterConstituent 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

ThornthwaiteMethod

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 waterfrom 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, overflowdams and open channels. Weirs can be sharp or broadcrested; made from concrete timber, or metal and can be ofcross-section rectangular, trapezoidal or triangular. Sharpcrested rectangular or triangular sections are commonlyused 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 ofcrest, H is the head on the crest and m is an exponent dependingon weir opening.

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Weirs should becalibrated todetermine theseparameters beforeuse eg. fortrapezoidalweirs(Cipolettiweir),

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 containingwater. The orifice can becircular, rectangular, triangularor any other shape. Thedischarge through an orifice isgiven 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 areParshall or Trapezoidal ones. Flumes need to be calibrated afterconstruction before use.

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For streams, use gauging. A current meter is used to measurevelocity at 0.2 and 0.8 Depth or at only 0.6 depth. Measure areasof 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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b) Integration Method: total area of interest divided into

sub plots as per crop growing or subdivided under crop, naturalvegetation, water ponds, bare land. The consumptive use thencalculated 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 frombarren land.

Once the value is obtained it can be expressed in terms of depth ofwater by dividing by the total area.

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c) Inflow & Outflow Studies: found for the total area

using the expression

Where, U = consumptive use of water in hect-m, I = totalinflow 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 = yearlyoutflow of the area. All values in hect – m.

RGGPIU es

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