irrigation necessity

7/28/2019 Irrigation Necessity

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IRRIGATION NECESSITYDr. H. Prashanth Reddy


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IRRIGATION

What is irrigation?

The process of artificial application of water to the

soil for the growth of agricultural crops is known as

irrigation

Why irrigation is required

Rainfall is not distributed evenly with time and space


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NECESSITYOFIRRIGATION

Less rainfall

Non-uniform rainfall (there may not be rain when

crop needed most)

Commercial crops require additional water Controlled water supply may be achieved with

irrigation


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FACTORSWHICHGOVERNTHENECESSITYOF

IRRIGATION

(1) insufficient rainfall

Seasonal rainfall is less than the minimum

requirement of crops

(2) Uneven distribution of rainfallUneven distribution of rainfall during the crop period

(3) to grow commercial crops

Crops like sugarcane, cotton require water throughout

the year


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FACTORSWHICHGOVERNTHENECESSITYOF

IRRIGATION

(4) development of agriculture in desert area

Rainfall is very scanty in desert areas and irrigation is

required for the development of agriculture


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MERITSOF IRRIGATION

(1) Yield of crops

Yield of crop during drought period may be increased

by irrigation

(2) Protection from famineThe food protection of country may be improved by

ensuring the growth of crops by irrigation

(3) Prosperity of farmers

Two or more crops may be grown in a year on thesame land


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DEMERITSOFIRRIGATION

(1) Rising of water table

The water table in the surrounding area of may be raisedand the soil may develop alkaline property

(2) Formation of damp conditions

The temperature of the commanded area may be loweredand that area may become damp

(3) Formation of marshy land

Excessive seepage and leakage of water from theirrigation canals may lead to marshy lands and become

breeding grounds for mosquitos (4) Loss of valuable lands

Valuable land may be get submerged when the storagereservoir are built


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RESOURCESOFIRRIGATION

(1) Rainfall

Runoff from rainfall is diverted to canal system by

weirs, barrages and dams

(2) Snow meltingRivers carry water from snow melting in summer can

be diverted to canal system

(3) ground water

Ground water is taken out with the help of pumps ,tube wells for irrigation purposes.


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TYPESOFIRRIGATIONSYSTEM

Three types of irrigation systems are available

(i) Gravity flow

(ii) Tank or reservoir irrigation

(iii) Lift irrigation


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TYPESOFIRRIGATIONSYSTEM

1. Gravity flow

Gravity flow irrigation is providing water due to

gravity without any mechanical means

2. Tank irrigation Small dams are constructed for the irrigation

purposes due to topography will not permit canal

irrigation system

3. Lift irrigation If water source is at the lower level than the supply

level then we try to supply water by using lift

irrigation.


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CLASSIFICATIONOFIRRIGATIONCANALS

1. Perennial canals

Water is available through out the year

2. Non-Perennial Canals

These are the canals which irrigate the field for onlyone part of the year

3. Inundation Canals

Inundation canals draw water only during periodical

rise of water in the river


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CLASSIFICATIONOFCANALSBASEDON

DISCHARGE

Main Canals

1. Main canals carries discharge directly from river.

2. It carries large supply of water (> 10 cumecs)

3. Not directly used for irrigation4. Supply water to branch canals


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DISCHARGE

Branch canal

The branch canal are taken off from either side of

the main canal at suitable points

The discharge varies from 5 to 10 cumecs

Distributory Canal

Distributory canals take off from branch canal

They supply water to field canals or water coursesthrough outlets.

Discharge varies from 0.25 to 3 cumecs


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DISCHARGE

Distributory canals divided as Major distibutory and

minor distributory

Major distibutory canals are taken off from maincanals. (Q between 0.25 to 3 cumecs)

Minor distributory canals are taken off from branch

canals. (Q between 0.25 to 3 cumecs)


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DISCHARGE

Field canals

These channels are taken off from the outlets of

distributory canals.

They supply water directly to fields Field canals are maintained by farmers


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CANALLINING

OBJECTIVESOF CANALLININGS

1. To control seepage losses

Seepage loss is maximum loss in unlined canals.

To balance seepage losses, capacity of the reservoir

has to be increased.

To control seepage lining of the canal is necessary.

2. To prevent water-logging

Leakage water from sides of canal inundates low lying

areas along the canal.

These low lying areas become alkaline and unsuitable

for agriculture

These low lying areas become breeding ground for

mosquitos


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CANALLINING


3. To increase the capacity of Canal

The velocity in unlined canal is fixed low to prevent

scouring and silting. (velocity < 1 m/s)

Discharge capacity of unlined canal is low To increase the discharge in an unlined canal, the

width of the canal needs to be increased which

involves more land required

4. To increase the command area Lining is required to prevent seepage losses and

ultimately command area of the project may be

enhanced.


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CANALLINING


5. To protect the canal from the flood damage

During heavy rains, high velocities in unlined canals

heavily scour and silt . To prevent the damage, the

lining should be provided


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CANALLINING


6. To control the growth of weeds

The growth of various types of weeds along the

sides of canals is a common problem

Some weeds are found to grow along the bed of thecanals

The weeds on the bed and sides reduce the flow

and capacity of the canals

Unlined canals require excessive maintenance forclearing the weeds.


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CANALLINING

TYPESOFLINING

Three types of canal lining are available

1. Plain cement concrete lining

2. Reinforced cement concrete lining

3. Brick lining


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CANALLINING

PLAINCEMENTCONCRETELINING

The plain cement concrete lining is done in

following steps.

(a) Preparation of sub-grade

Subgrade is prepared by compacting the surfaceproperly with a layer of sand (15 cm thick)

The slurry of cement and sand (1:3) is spread

uniformly over the prepared bed.


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CANALLINING

PLAINCEMENTCONCRETELINING

(b) Laying concrete

The cement concrete of grade M15 is spread

uniformly according to the desired thickness.

After laying, the concrete is tapped gently until theslurry comes on the top.

The curing is done for 2 weeks

Expansion joints are provided to take care of

expansion of concrete


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CANALLINING

BRICKLINING

This lining is prepared by the double layer brick flat

soling laid with cement mortar (1:6) over the

compacted sub-grade.

First class bricks are recommended for this

purpose.

The surface of the lining is finished with cement

plaster (1:3). The curing should be done perfectly.

The brick lining is preferred for the following

reasons


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CANALLINING

BRICKLINING

Advantages of brick lining

(i) brick lining is economical

(ii) work can be done very quickly

(iii) expansion joints are not required (iv) repair works can be done easily

(v) Bricks available locally


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CANALLINING

BRICKLINING

Disadvantages of brick lining

(i) it is not completely impervious

(ii) It has low resistance against erosion

(iii) it is not so much durable


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CANALLINING

REINFORCEDCEMENTCONCRETELINING

Reinforcement is required to increase the

resistance against cracks and shrinkage cracks.

The reduction in the cracks results in less seepage

losses.

The RCC lining is expensive (15%) and not used

frequently.


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ADVANTAGESOF CANAL LINING

1. It reduces the loss of water due to seepage and

hence the duty is enhanced.

2. It controls the water logging and hence

consequences are eliminated.

3. It provides smooth surface and hence the

velocity of flow can be increased

4. discharge capacity of the channel is also

increased


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ADVANTAGESOF CANAL LINING

It eliminates the effect of scouring in the canal bed

The increased velocity eliminates the possibility of

silting in the canal bed

It controls the growth of weeds along the canal

sides and bed

It provides stable cross section

It reduces requirement of land width for the canal

It reduces the maintenance cost


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DISADVANTAGESOF CANAL LINING

1. The initial cost of the canal lining is very high

2. Difficulties in repairing the damaged section of

lining.

3. It takes longer to complete the project work

4. It becomes difficult, if the outlets are required to

be shifted or new outlets are required to be

provided.


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FACTORSAFFECTINGTYPEOFLINING

(1) Imperviousness

When the canal passes through the sandy soil the

seepage loss is maximum and the canal is unstable.

Cement concrete lining is required for this kind of

situation.

(2) Smoothness

Smoothness of canal lining increase the flow rate in

the canal. Cement concrete lining gives smooth

surface to the canal


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(3) Durability

To make the canal section more durable against all

adverse effects like scouring, erosion and weather

action, etc. cement concrete lining is required

(4) Economy

The lining should be economically viable with

benefits that may be accrued from the expected

revenue, yield of crop etc.


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(5) Site condition

The canal may pass through marshy land, loose

sandy soil, alluvial soil, black clayey soil and hard soil

etc., lining is recommended according to type

(6) Life of project

Lining is required depends on the canal design to

serve how long in future


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(7) Availability of construction materials

The expenditure of lining depends on the availability

of construction materials locally, transportation

charges of materials to the site.


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MANNINGSROUGHNESSCOEFFICIENTSFOR

DIFFERENTTYPESOFLINING

Bricklining 0.014 to 0.017

Earth lining: 0.02

PCC: 0.014

RCC: 0.012

irrigation necessity

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