Date post: | 03-Apr-2018 |
Category: |
Documents |
Upload: | prashanthreddyh |
View: | 228 times |
Download: | 0 times |
of 37
7/28/2019 Irrigation Necessity
1/37
IRRIGATION NECESSITYDr. H. Prashanth Reddy
7/28/2019 Irrigation Necessity
2/37
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
7/28/2019 Irrigation Necessity
3/37
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
7/28/2019 Irrigation Necessity
4/37
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
7/28/2019 Irrigation Necessity
5/37
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
7/28/2019 Irrigation Necessity
6/37
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
7/28/2019 Irrigation Necessity
7/37
7/28/2019 Irrigation Necessity
8/37
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
7/28/2019 Irrigation Necessity
9/37
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.
7/28/2019 Irrigation Necessity
10/37
TYPESOFIRRIGATIONSYSTEM
Three types of irrigation systems are available
(i) Gravity flow
(ii) Tank or reservoir irrigation
(iii) Lift irrigation
7/28/2019 Irrigation Necessity
11/37
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.
7/28/2019 Irrigation Necessity
12/37
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
7/28/2019 Irrigation Necessity
13/37
7/28/2019 Irrigation Necessity
14/37
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
7/28/2019 Irrigation Necessity
15/37
CLASSIFICATIONOFCANALSBASEDON
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
7/28/2019 Irrigation Necessity
16/37
CLASSIFICATIONOFCANALSBASEDON
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)
7/28/2019 Irrigation Necessity
17/37
CLASSIFICATIONOFCANALSBASEDON
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
7/28/2019 Irrigation Necessity
18/37
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
7/28/2019 Irrigation Necessity
19/37
CANALLINING
OBJECTIVESOF CANALLININGS
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.
7/28/2019 Irrigation Necessity
20/37
CANALLINING
OBJECTIVESOF CANALLININGS
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
7/28/2019 Irrigation Necessity
21/37
CANALLINING
OBJECTIVESOF CANALLININGS
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.
7/28/2019 Irrigation Necessity
22/37
CANALLINING
TYPESOFLINING
Three types of canal lining are available
1. Plain cement concrete lining
2. Reinforced cement concrete lining
3. Brick lining
7/28/2019 Irrigation Necessity
23/37
7/28/2019 Irrigation Necessity
24/37
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.
7/28/2019 Irrigation Necessity
25/37
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
7/28/2019 Irrigation Necessity
26/37
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
7/28/2019 Irrigation Necessity
27/37
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
7/28/2019 Irrigation Necessity
28/37
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
7/28/2019 Irrigation Necessity
29/37
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.
7/28/2019 Irrigation Necessity
30/37
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
7/28/2019 Irrigation Necessity
31/37
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
7/28/2019 Irrigation Necessity
32/37
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.
7/28/2019 Irrigation Necessity
33/37
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
7/28/2019 Irrigation Necessity
34/37
FACTORSAFFECTINGTYPEOFLINING
(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.
7/28/2019 Irrigation Necessity
35/37
FACTORSAFFECTINGTYPEOFLINING
(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
7/28/2019 Irrigation Necessity
36/37
FACTORSAFFECTINGTYPEOFLINING
(7) Availability of construction materials
The expenditure of lining depends on the availability
of construction materials locally, transportation
charges of materials to the site.
7/28/2019 Irrigation Necessity
37/37
MANNINGSROUGHNESSCOEFFICIENTSFOR
DIFFERENTTYPESOFLINING
Bricklining 0.014 to 0.017
Earth lining: 0.02
PCC: 0.014
RCC: 0.012