Chapter - 1 Irrigation Engineering

7/29/2019 Chapter - 1 Irrigation Engineering

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Irrigation Engineering


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Definition

Irrigation may be defined as the process of artificially supplying water to

soil for full-fledged nourishment of the crops.

In other words, it is the science of artificial application of

water to the land in accordance with the 'crop requirements' throughout

the 'crop period'.

Irrigation Engineering includes the study of system of different irrigation

methods and design of works in connection with river control, generation

of hydroelectric power, drainage of water-logged areas.

Irrigation may be defined as in other words it is the requirement of water

to the soil for raising the crops.


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Necessity of Irrigation (In INDIA)

India is a Tropical country with varieties of climate, topography and

vegetation.

We have an agrarian economy and many resources depend on the

agricultural output.

For maximum crop productivity it is very essential to supply the optimum

quantity of irrigation water at proper timings.

Irrigation water performs number of important function, e.g. acts as

nutrient and moisture carrier, ensures better utilization of chemicalfertilizer, and maintain optimum temperature around plant environment.


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Important major irrigation projects in India


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Irrigation is necessary for the following reasons

Scanty Rainfall

Non-Uniform Rainfall

Increasing Yield in Dry Farming

Practicing Crop Rotation Controlled Water supply


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Scanty Rainfall

In India, many areas like Rajasthan receives very less rainfall.

These areas need irrigation water, in such cases, irrigation works may beconstructed at the places where quantity of water is available and we can

convey the water to such areas where there is deficiency of water.

Non-Uniform Rainfall

In India, there is large spatial and temporal variation in precipitation.

Thus, the rainfall is not uniform at all the zones. The rainfall during the

winter is very scanty and therefore rabi crops need the artificial supply of

water by the irrigation works.

Increasing Yield in Dry Farming

Dry farming depends upon natural rainfall. Agriculture which deals with

rainfall only is called dry farming.


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Practicing Crop Rotation

To bring in rotation of crops, i.e. if we want that the more number of crops

should be rotated then there, will be need of irrigation water.

Controlled Water supply

As irrigation serves the following important purposes :

It can save the crops from drying during short duration droughts.

It washes out or dilutes salts in soil. It cools the soil and also the atmosphere and makes more favorable

environment for healthy plant growth

The construction of proper distribution system may ensure

proper irrigation water supply thus, the yield of the crop can be increasedeven there is limited water supply. Proper irrigation system checks water

losses during irrigation.


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Importance of Irrigation

The rainfall of our country is dependent on the monsoons. Rainfall

controls our agriculture. But the agriculture of our country is said to be,"the gambling of the monsoon" as the monsoon rainfalls are uncertain,

irregular and uneven or unequal. So irrigation is essential for agriculture.

The following are the primary reasons of irrigation in our country.

About 80 per cent of the total annual rainfall of India occurs in four

months, i.e. from mid-June to mid-October. So it is essential to provide

irrigation for production of crops etc, during the rest of the eight months.

The monsoons are uncertain. So irrigation is necessary to protect crops

from drought as a result of uncertain rainfall.

It does not rain equally in all parts of the country. So irrigation is necessary

for agriculture in less rainfall areas.


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Soils of some areas are sandy and loamy and therefore porous for which a

major portion of rainwater sinks down very quickly.

So, sandy and loamy soils can't retain water like the alluvialsoil and the black soil. That is why irrigation is essential for farming in the

areas having, sandy and loamy soils.

The rain-water flows down very quickly along the slopes of hillsides. So

irrigation is necessary to grow crops in such areas.

India is an agricultural and populous country. About 70 per cent of people

depend on agriculture. In order to grow food-crops and agricultural

products in large quantities to feed the growing millions, intensive farming

and rotation of crops are essential. Extensive irrigation is, therefore,necessary for more production.


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Advantages of Irrigation

Irrigation is one of the vital input of agricultural production system. In fact,

with the development of irrigation and with other technological inputs the

country could increase its grain production more than four times since

independence.

A wide variation in irrigation exists in Indian states and so is the variation

in the grain yield in different states.


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The following are the advantages of Irrigation :

Increase in food production

Optimum benefits

Elimination of mixed cropping

General Prosperity

Generation of hydroelectric power

Domestic water supply

Facilities of communications

Inland Navigation

Afforestation


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Increase in food production


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Optimum Benefits


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Elimination of MixedCropping


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General Prosperity


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Hydro electric power generation


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Domestic water supply


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Facilities of Communications


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Inland Navigation


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Afforestation


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Disadvantages of Irrigation

Proper management of water is necessary for good natural resource

management and sustainable yield.

The excess irrigation and unscientific use of irrigation water may give rise

to the following ill effects.

The disadvantages of excessive irrigation may be listed as follows : Wasteful use of water

Water logging

Soil degradation in irrigated areas

Contamination of water with harmful substances

Damp climate and Ecological imbalances

Mosquitoes breeding


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Types of Irrigation

Sources of irrigation water are either surface water (direct or

stored) or ground water (to be tapped through bored wells

using pumping system)

Irrigation may broadly be classified into :

Surface Irrigation

Sub-surface irrigation


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Surface Irrigation

In this type of irrigation water wets the soil surface

It can be further classified into :

Flow Irrigation

When water is supplied from higher level to lower level by the action ofgravity then it is called flow irrigation.

The irrigation from canal water or river water is the example of flow

irrigation.

Lift Irrigation

When water is lifted up by any manual or mechanical means such as

Persian wheel, pumps, etc. and then supplied for irrigation then it is called

lift irrigation.


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Flow Irrigation


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Lift Irrigation


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Flow irrigation can be further subdivided into :

(a) Perennial irrigation (b) Flood irrigation

Perennial Irrigation

In this type of irrigation system, the water requirement for irrigation is

supplied constantly and continuously in accordance with crop

requirements throughout the crop period.

In this system of irrigation, water is supplied through the storage canalhead works and canal distribution system.

Flood Irrigation

This kind of irrigation is some times called as Inundation irrigation.

In this method of irrigation soil is kept submerged and flooded with water,

so as to cause thorough saturation of the land.


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Perennial canal system may be further sub-divided as follows :

Direct Irrigation When irrigation is done from direct run off of a river, or by diverting the

river run off water into some canal by constructing a diversion weir or

barrage across the river. For example, Ganga Irrigation canal system.

Storage Irrigation When a dam is constructed across a river to store water during the

monsoon and the stored water is supplied in the off taking channels

during periods of low flow, it is called storage irrigation.

For example, Ram Ganga dam project in UP. In coastal areas where rivers

are not perennial storage irrigation becomes a necessity.

However, It is more costly and difficult to construct.


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Sub-surface Irrigation

In this type of irrigation, water does not wet the soil surface.

In this system of irrigation the supplied water comes directly in touch with

root zone of the crops.

This system of irrigation may be employed usefully under the following

conditions :

Topography conditions of area are uniform.

Land slope is moderate.

The quality of irrigation water is good.

The soil in the root zone is permeable in nature.


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Sub surface irrigation

Sub surface irrigation may be classified into two types

(a) Natural sub irrigation (b) Artificial sub irrigation.

Natural Sub-irrigation

When underground irrigation can be achieved simply by natural

processes without any extra efforts it is called natural sub-Irrigation.

In fact leakage water from channel, etc. goes underground and during

seepage through the sub soil, it may irrigate the crop in the lower lands

Artificial Sub-irrigation

The open jointed system of drain is artificially laid below the soil so as to

supply the water to the crop by capillary action, then it is known as

artificial sub-irrigation.

This process is not adopted in India because it is very costly.


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Classification of Irrigation Projects

1. Based on Type of Reservoir

There are various methods of classification of irrigation projects or

schemes :

(a) Storage or conservation reservoirs

(b) Flood control reservoirs

(c) Distribution reservoirs(d) Multipurpose reservoirs

2. Source Wise Classification

3. Distribution System Wise

4. Location Wise


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Storage or Conservation Reservoirs

A reservoir can be used for controlling floods or in addition to other

purposes. In former case it is known as Flood control reservoir and in later

case it is called a 'Multipurpose Reservoir'.

Flood Control Reservoirs

A Flood control reservoir stores a portion of flood flows in such a way as

to minimize the flood peaks at the areas to the protected downstream.

Distribution Reservoirs

A distribution reservoir is a small Storage reservoir constructed

within a city water supply system.

Multipurpose Reservoirs

When any reservoir is planned and constructed to serve not only one

purpose but various purposes together is called multipurpose reservoirs.

When reservoir is serving the purposes like water supply, irrigation, industrial

needs, multipurpose reservoir. Ex: Bhakra dam and Nagarj


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Source Wise Classification

This may be based on the source of irrigation water like direct, indirect and

ground water.

As presented earlier, the practice of direct irrigation is normally in north India

on perennial rivers of Indo- Gangetic plain and also in coastal areas.

Direct irrigation is the best economical and reliable system of irrigation. More than 40% land is irrigated by this type of irrigation.

The indirect irrigation is that type of irrigation in which the water is stored in

reservoirs and can be taken out when it is needed.

It is uneconomical.

In the lift irrigation, water is lifted up from source.

This is very costly and less reliable.


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Distribution System Wise

It can be classified as Flow and Lift.

When the source is situated at higher level and the area is to be irrigated,the water flows by gravity.

In lift irrigation the water source is at lower level. It totally depends up on

lifting machinery and, it is costly and less reliable.

LocationWise

Irrigation project may be classified on location wise as valley or delta.

If the project is located in a river it may be called as valley project while

project is located in delta of a river it may be called delta-irrigation.


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Irrigation Schemes of India

The Schemes of irrigation used in India can be broadly classified into major,

medium and minor irrigation schemes.

Major Irrigation Schemes

Medium Irrigation Schemes

Minor Irrigation Schemes

Irrigation projects having Culturable Command Area (CCA) of more than

10,000 hectares each are classified as major projects.

Those having a CCA between 2,000 hectares and 10,000 hectares fall

under the category of medium irrigation projects.

The projects which have a CCA of less than 2,000 hectares are classified as

minor irrigation schemes.


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For the purpose of analysis the major and the medium irrigation projects

are generally grouped together.

These projects comprise a network of dams, bunds, canals and other

such schemes.

Such projects require substantial financial outlay and are, therefore,

constructed by the government or any other agency which may draw

financial assistance form the government and financial institutions.

The minor irrigation projects, on the other hand, comprise all ground

water development schemes such as dug wells, private shallow tube wells,

deep public tube wells, and boring and deepening of dug wells, and small

surface water development works such as storage tanks, lift irrigation

projects, etc. Minor irrigation projects or the groundwater development schemes are

essentially people's programmes implemented primarily through

individual and cooperative efforts with finances obtained mainly through

institutional sources.


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Methods of application of Irrigation water

(or) Techniques of water distribution in the forms

There are various ways in which irrigation water can be applied to the fields

Their main classification is as follows:

Free flooding

Border flooding Check flooding

Basin flooding

Furrow irrigation method

Sprinkler irrigation method

Drip irrigation method


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Free flooding


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Free flooding

Also called as ordinary flooding, Wild flooding, Uncontrolled flooding.

Ditches are excavated in the field, they may be either on the contour or up

the slope or down the slope.

Water from these ditches , flows across the field.

After the water leaves the ditches, no attempt is made to control the flow by

means of levees etc.

Since the movement of water is not restricted, it is sometimes called as Wild

flooding.


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Although the initial cost of the land preparation is low, labor requirements

are usually high and water application efficiency is also low.

Wild flooding is most suitable for close growing crops, pastures, etc.

particularly where the land is steep.

Contour ditches called laterals or subsidiary ditches, are generally spacedat about 20 to 50m apart, depending upon the slope, texture of soil, crops

to be grown, etc.

This method may be used on the rolling land(topography irregular) where

borders, checks, basins and furrows are not feasible.


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Boarder flooding


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Border flooding

The land is divided into no. of strips, separated by low levees calledborders.

The land areas confined in each strip is of the order of 10 to 20 m in widthand 100 to 400 m in length.

Ridges between the borders should be sufficiently high to prevent

overtopping during irrigation.

To prevent water from concentrating on either side of the border, the landshould be leveled perpendicular to the direction of flow.

Water is made to flow from the supply ditch into each strip.

The water flows slowly towards the lower end, and infiltrates into the soilas it advances.


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When the advancing water reaches the lower end of the strip, the supply of

water to the strip is turned off.

The supply ditch, also called irrigation stream, may either be in the form of anearthen channel or a lined channel or an underground concrete pipe having

risers at intervals.

The size of supply ditch depends upon the infiltration rate of the soil, and the

width of border strip.

Coarse textured soils with high infiltration rate of the soil, will require high

discharge rate and therefore, larger supply ditch, in order to spread the water

over the entire strip rapidly and to avoid excessive losses due to deep

percolation at the upper reaches.

Fine textured soils with low infiltration rates, require smaller ditches to avoid

excessive losses due to runoff at the lower reaches.


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A relationship between the discharge through the supply ditch (Q), the

average depth of water flowing over the strip(y), the rate of infiltration of

the soil (f), the area of the land irrigated (A), and the approximate time

required to cover the area with water (t), is given by the equation :

Where Q = Discharge through the supply ditch

y = Depth of water flowing over the border strip,

f = Rate of infiltration of soil

A = Area of land strip to be irrigated

t = Time required to cover the given area A


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Check flooding

h k l di


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Check Flooding


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Check Flooding

It is similar to ordinary flooding except that the water is controlled bysurrounding the check area with low and flat levees.

Levees are generally constructed along the contours, having verticalinterval of about 5 to 10cm.

These levees are connected with cross levees at convenient places (see inabove picture)

The confined plot area varies from 0.2 to 0.8 ha

In this method, the check is filled with water at fairly high rate and allowedto stand until the water infiltrates.


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This method is suitable for more permeable soils as well as less permeable

soils.

The water can be quickly spread in case high permeable soils, thus

reducing the percolation losses.

The water can also be held on the surface for a longer time in case of less

permeable soils, for assuring adequate penetration.

These checks are sometimes used to absorb the water, where the stream

flow is diverted during periods of high runoff.


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Basin flooding


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Basin Flooding

This method is special type of check

flooding and is adopted for orchard trees.

One or more trees are generally placed

in the basin, and the surface is flooded as

in the check method, by ditch water.


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Furrow Irrigation Method


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In furrow irrigation method only one-fifth to one-half of the land surface iswetted by water, thus it results in less evaporation, less pudding of soil,and permits cultivation sooner after irrigation.

Furrows are narrow field ditches, excavated between rows of plants andcarry irrigation water through them

Spacing of furrows is determined by the proper spacing of the plants.Furrows vary from 8 to 30cm deep, and may be as much as 400m long.

Excessive long furrows may result in too much percolation near the upperend, and too little water near the down-slope end.

Deep furrows are widely used for row crops.

Small shallow furrows called corrugations are particularly suitable forrelatively irregular topography and close growing crops, such as meadowsand small grains


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Water can be diverted into the furrows by

an opening in the bank of the supply ditchor preferably by using a rubber hose

tubing, which can be permitted by

immersion in the ditch.


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Advantages of Furrow Irrigation

Irrigation streams can be large or small because the number of rows irrigated

at one time can be adjusted as needed according to the available flow.

Efficient application can be obtained if water management practices are

followed and the land has been properly prepared.

The initial capital investment is relatively low on lands not requiring extensive

land leveling, since the furrows and corrugations are constructed by commonly

used farm implements.

The water distribution systems do not normally require high water pressure tooperate; therefore, pumping costs are relatively low.

Soils that form surface crusts when irrigated by flood methods can be readily

irrigated by furrows because water moves across the row under the surface


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Limitations of Furrow Irrigation

Salts from either the soil or water supply may concentrate in the ridges and

depress crop yields. The lateral spread of water in some soils is not adequate to provide full

irrigation.

The difference in intake opportunity time along the furrow due to the time

required for the stream to advance makes it difficult to obtain uniform

application depths. Corrugations create a rough field surface difficult to cross with harvesting and

other farm equipment.

The soil-erosion hazard limits use to land having very little slope.

Labor requirements may be high because irrigation streams must be carefully

regulated to achieve uniform water distribution.

Leaching of salts is difficult or impossible.

Land leveling is normally required to provide uniform furrow grades.


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Sprinkler irrigation method


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Sprinkling is the method of applying water to the soil surface in the form

of a spray which is somewhat similar to rain.

In this method, water is sprayed into the air and allowed to fall on the soil

surface in a uniform pattern at a rate less than the infiltration rate of the

soil.

This method is popular in the developed countries and is gaining

popularity in the developing countries too.

Rotating sprinkler-head systems are commonly used for sprinkler

irrigation.

Each rotating sprinkler head applies water to a given area, size of which is

governed by the nozzle size and the water pressure.


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Alternatively, perforated pipe can be used to deliver water through verysmall holes which are drilled at close intervals along a segment of the

circumference of a pipe.

The trajectories of these jets provide fairly uniform application of water

over a strip of cropland along both sides of the pipe. With the availabilityof flexible PVC pipes, the sprinkler systems can be made portable too.

Sprinklers have been used on all types of soils on lands of different

topography and slopes, and for many crops.


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The following conditions are favorable for sprinkler irrigation :

Very previous soils which do not permit good distribution of water bysurface methods,

Lands which have steep slopes and easily erodible soils

Irrigation channels which are too small to distribute water efficiently by

surface irrigation

Lands with shallow soils and undulating lands which prevent proper

leveling required for surface methods of irrigation.


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Besides, the sprinkler system has several features.

For example, small amounts of water can be applied easily and

frequently by the sprinkler system.

Light and frequent irrigations are very useful during the germination of new

plants, for shallow-rooted crops and to control soil temperature.

Measurement of quantity of water is easier.

It causes less interference in cultivation and other farming operations.

While sprinkler irrigation reduces percolation losses, it increases evaporation

losses.


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The frequency and intensity of the wind will affect the efficiency of any

sprinkler system.

Sprinkler application efficiencies should always be more than 75 per cent

so that the system is economically viable.

The sprinkler method is replacing the surface/gravity irrigation methods in

all developed countries due to

Its higher water application/use efficiency

less labor requirements

Adaptability to hilly terrain Ability to apply fertilizers in solution


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Drip Irrigation Method


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Drip irrigation, also called as trickle irrigation, is the latest field irrigation

technique, and is meant for adoption at places where there exists acute

scarcity of irrigation water and other salt problems.

Water is slowly and directly applied to the root zone of the plants, thereby

minimizing the losses by evaporation and percolation.

This system comprises of heads, mains, sub- mains, laterals, valves (to

control the flow), drippers or emitters (to supply water to the plants),

pressure gauges, water meters, filters (to remove all debris, sand and clay

to reduce clogging of the emitters), pumps, fertilizer tanks, vacuum

breakers and pressure regulators.

Water oozes out of these small drip nozzles or drippers uniformly and at a

very small rate, directly into the plant roots area.

Th d i d i d t l t t th d i d t (1 t 10


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The drippers are designed to supply water at the desired rate (1 to 10

litres per hour) directly to the soil.

Low pressure heads at the emitters are considered adequate as the soil

capillary forces cause the emitted water to spread laterally and vertically. Flow is controlled manually or set to automatically either

deliver desired amount of water for a predetermined time, or

supply water whenever soil moisture decreases to a predetermined

amount.

Drip irrigation has several advantages

It saves water

enhances plant growth and crop yield

saves labor and energy controls weed growth

causes no erosion of soil

does not require land preparation

and also improves fertilizer application efficiency


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However, this method of irrigation does have some economic and

technical limitations. It requires high skill in design, installation, and

subsequent operation.

Trickle irrigation enables efficient water application in the root zone of

small trees and widely spaced plants without wetting the soil where no

roots exist.

In arid regions, the irrigation efficiency may be as high as 90 per cent and

with very good management it may approach the ideal value of 100 per

cent.

Insect, disease, and fungus problems are also reduced by minimizing the

wetting of the soil surface.


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The main reasons for the high efficiency of trickle irrigation are its

capability to produce and maintain continuously high soil moisture

content in the root zone and the reduction in the growth of weeds (due to

limited wet surface area) competing with the crop for water and nutrients.

Due to its ability to maintain a nearly constant soil moisture content in the

root zone, trickle irrigation results in better quality and greater crop yields.

Fruits which contain considerable moisture at the time of harvesting (such

as tomatoes, grapes, berries, etc.) respondvery well to trickle irrigation.

However, this method is not at all suitable (from practical as well as

economic considerations) for closely planted crops such as wheat andother cereal grains.


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One of the major problems of trickle irrigation is the clogging of small

conduits and openings in the emitters due to sand and clay particles,

debris, chemical precipitates, and organic growth.

In trickle irrigation, only a part of the soil is wetted and, hence it must be

ensured that the root growth is not restricted.

Another problem of trickle irrigation is on account of the dissolved salt leftin the soil as the water is used by the plants.

If the rain water flushes the salts near the surface down into the root

zone, severe damage to the crop may result.

In such situations, application of water by sprinkler or surface irrigation

may become necessary.


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All the methods have some advantages and disadvantages, and the choice of

the method depends on the following factors :

Size, shape, and slope of the field

Soil characteristics

Nature and availability of the water supply subsystem

Types of crops being grown

Initial development costs and availability of funds

Preferences and past experience of the farmer

The design of an irrigation system for applying water tocroplands is quite complex and not amenable to quantitative analysis.


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Principal criteria for the design of a suitable irrigation method are as follows :

Store the required water in the root-zone of the soil Obtain reasonably uniform application of water

Minimize soil erosion

Minimize run-off of irrigation water from the field

Provide for beneficial use of the runoff water

Minimize labor requirement for irrigation

Minimize land use for ditches and other controls to distribute water

Fit irrigation system to field boundaries

Adopt the system to soil and topographic changes

Facilitate use of machinery for land preparation, cultivating, furrowing,harvesting and so on.


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Soils

Soil mainly consists of finely divided organic matter and minerals (formeddue to disintegration of rocks).

It holds the plants upright, stores water for plant use, supplies nutrients to

the plants and helps in aeration.

Soils can be classified in many ways, such as on the

basis of size (gravel, sand, silt, clay, etc.)

geological process of formation, and so on.

Based on their process of formation (or origin) they can be classified into the


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Based on their process of formation (or origin), they can be classified into the

following categories:

Residual soils: Disintegration of natural rocks due to the action of air,moisture, frost, and vegetation results in residual soils.

Alluvial soils: Sediment material deposited in bodies of water, deltas, and

along the banks of the overflowing streams forms alluvial soils.

Aeolian soils: These soils are deposited by wind action.

Glacial soils: These soils are the products of glacial erosion.

Colluvial soils: These are formed by deposition at foothills due to rain wash.

Volcanic soil: These are formed due to volcanic eruptions and are commonly

called as volcanic wash


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The soils commonly found in India can be classified as follows:

Alluvial Soils:

Alluvial soils include the deltaic alluvium, calcareous alluvial soils, coastal

alluvium, and coastal sands.

This is the largest and most important soil group of India.

The main features of the alluvial soils of India are derived from the deposition

caused by rivers of the Indus, the Ganges, and the Brahmaputra systems.

These rivers bring with them the products of weathering of rocks constituting

the mountains in various degrees of fineness and deposit them as they

traverse the plains.

These soils vary from drift sand to loams and from fine silts to stiff clays.

Such soils are very fertile and, hence, large irrigation schemes in areas of suchsoils are feasible.

However, the irrigation structures themselves would require strong

foundation.

Black Soils


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The black soils vary in depth from a thin layer to a thick stratum.

The typical soil derived from the Deccan trap is black cotton soil.

It is common in Maharashtra, western parts of Madhya Pradesh, parts of

Andhra Pradesh, parts of Gujarat, and some parts of Tamil Nadu.

These soils may vary from clay to loam and are also called heavy soils.

Many black soil areas have a high degree of fertility but some, especially in the

uplands, are rather poor.

These are suitable for the cultivation of rice and sugarcane.

Drainage is poor in such soils.

Red Soils

These are crystalline soils formed due to meteoric weathering of the ancient

crystalline rocks.

Such soils are found in Tamil Nadu, Karnataka, Goa, south-eastern Maharashtra,eastern Andhra Pradesh, Madhya Pradesh, Orissa, Bihar, and some districts of

West Bengal and Uttar Pradesh.

Many of the so-called red soils of south India are not red.

Red soils have also been found under forest vegetation.


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Lateritic Soils

Laterite is a formation peculiar to India and some other tropical countries.

Laterite rock is composed of a mixture of the hydrated oxides of aluminium and

iron with small amounts of manganese oxides.

Under the monsoon conditions, the siliceous matter of the rocks is leached

away almost completely during weathering.

Laterites are found on the hills of Karnataka, Kerala, Madhya Pradesh, the

estern Ghats of Orissa, Maharashtra, West Bengal, Tamil Nadu, and Assam.

Desert Soils

A large part of the arid region belonging to western Rajasthan, Haryana, and

Punjab lying between the Indus river and the Aravalli range is affected by desert

and conditions of geologically recent origin.

This part is covered with a mantle of the blown sand which, combined with thearid climate, results in poor soil development. The Rajasthan desert is a vast

sandy plain including isolated hills or rock outcrops at places.

The soil in Rajasthan improves in fertility from west and north-west to east and

north-east.


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Forest Soils

These soils contain high percentage of organic and vegetable matter and

are also called humus.

These are found in forests and foothills.

Soils suitable for agriculture are called arable soils and other soils are non

arable.

Depending upon their degree of arability, these soils are further subdivided as

follows:

Class I: The soils in class I have only a few limitations which restrict their

use for cultivation. These soils are nearly level, deep, well-drained, and

possess good water-holding capacity. They are fertile and suitable forintensive cropping.

Class II: These soils have some limitations which reduce the choice of

crops and require moderate soil conservation practices to prevent

deterioration, when cultivated.

Class III: These soils have severe limitations which reduce the choice of


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Class III: These soils have severe limitations which reduce the choice of

crops and require special soil conservation measures, when cultivated.

Class IV: These soils have very severe limitations which restrict the choice ofcrops to only a few and require very careful management. The cultivation

may be restricted to once in three or four years.

Soils of type class I to class IV are called arable soils.

Soils inferior to class IV are groupedas non-arable soils.

Irrigation practices are greatly influenced by the soil characteristics. From

agricultural considerations, the following soil characteristics are of

particular significance.

(i) Physical properties of soil,

(ii) Chemical properties of soil, and

(iii) Soil-water relationships.

Documents

Chapter - 1 Irrigation Engineering