2. Module-II
• Methods of Irrigation:
• Classification- choice of method of irrigation- surface
and subsurface irrigation methods, Sprinkler and Drip
Irrigation
• Irrigation channels:
• Alignment- canal capacity- losses- FSL of canal-
design of canal in alluvial soil and non alluvial
soils- Kennedy’s silt theory- Lacey’s regime theory-
balancing depth- use of Garrets diagrams and Lacey’s
Regime diagrams- lining of irrigation channels-
design of lined canal- drainage behind lining. Water
logging: Causes, Measures: surface and sub-surface
drains, land reclamation
3. Methods of Water Distribution to Crop
Fields
• The chapter deals with the different methods
of water distribution to the crops like furrow
method, contour farming, flooding method,
boarder strips, contour laterals, sprinkler
irrigation and drip irrigation methods.
4. Surface Irrigation Method
• Furrow Method
• In this method, irrigation water is useful for row
crops. Narrow channels are dug at regular
intervals. Water from the main supply is allowed
to enter these small channels or furrows. Water
from the furrows infiltrates into soil and spread
laterally to saturate the root zone of the crops. It
is suitable for row crops like potatoes, sugarcane,
tobacco, maize, groundnut, cotton, jowar, etc..
6. Furrow Method
• This method has the following advantages:
• Less water is required as water comes in
contact of 1/5 to ½ of the land surface.
• Evaporation loss is less.
• Labor requirement for land preparation and
irrigation is less.
• Wastage of water is minimum.
• It is suitable for row crops.
8. Contour Farming
• Contour farming is practiced in hilly areas
with slopes and with falling contour. The land
is divided into series of horizontal strips called
terraces. Small bunds are constructed at the
end of each terrace to hold water up to equal
height. Contour farming besides producing
crop yields, helps in mitigating indirectly
controlling flood, soil conservation.
11. Flooding Method
• The flooding method is subdivided into various
methods as:
• Free Flooding
• With the help of field channels, agricultural land
is divided into small strips . Field channels are
provided with the field regulator. This method is
known as irrigation by plots commonly used in
India.
• In this method when the strips are flooded with
water, surplus water is allowed to enter the
water channel and allowed to discharge in the
water downstream.
13. Basin Flooding
• This method is used frequently to irrigate the
orchards. It is a special type of check flooding
method. Each plant is enclosed by circular
channels which is called basin. Basins are
connected to small field ditches.
• Ditches are fed from the main supply channel.
When the basin are flooded, the supply is
stopped. Portable pipes or large hoses may also
be used in place of ditches to flood the basin
16. Check Flooding
• In check flooding the crop area is divided into
some plots which are relatively leveled by
checks or bunds water from field channels is
allowed to enter to each plot or check basin
and the plots are flooded to the required
depth.
18. Border Strips
• In this method, the agricultural area is divided into
series of long narrow strips known as border strips
by levees, i.e. small bunds. The strips are aligned
along the country slope so that the water can flow
easily throughout the area. This method is suitable
when the area is at level with gentle country slope.
20. Zig-Zag Method
• In this method, the agricultural area is sub-
divided into small plots by low bunds in a zig-
zag manner. The water is supplied to the plots
from the field channel through the openings.
The water flows in a zig-zag way to cover the
entire area. When the desired depth is
attained, the openings are closed.
21. Sprinkler Irrigation Method
• In this method, water is applied to the crop in the form
of sprinkle or spray with the combination of pump, main
pipe, sub-main pipe, lateral, riser, nozzle, etc..
• It is a kind of artificial rainfall and therefore, it is very
fruitful for crops grown in a farm.
• This method is useful where:
• Surface irrigation method is not sufficient
• Slope of the crop field is higher
• Topography of the crop field is irregular
• Soil is erosive.
• Depth of soil is shallow over gravel and sand.
25. Advantages and Dis-advantages of
Sprinkler Irrigation
• Advantages:
• Erosion of soil is avoided or controlled
• It is possible to apply water uniformly
• Irrigation of water better controlled according to need of the crops in
their different stages of growth.
• There is no surface run-off
• Labor cost is less
• Damage of crop due to frost is reduced.
• It is a standby drainage pumping set
• It can be used even with high water table.
• Seepage loss like earthen canal are eliminated
• Fertilizers can be uniformly applied by mixing with water.
• Efficiency is higher,
• i.e. Efficiency = Water stored in root zone
Water sprinkled
26. Advantages and Dis-Advantages of
Sprinkler Irrigation
• Dis-Advantages:
• Although this method has number of advantages, yet it has
some limitations
• Wind may disturb or distort sprinkling pattern
• A constant water supply is needed for commercial use of
equipment.
• Water is to be clean and free from sand.
• Heavy soil with pore intake cannot be irrigated efficiently.
• Areas with higher temperature increase evaporation loss
• They are not suitable for crops requiring frequent and
deep water depth.
• It requires high electrical power.
27. Drip or Trickle Irrigation
• It has been shown that sprinkler irrigation is not suitable in the region of
high temperature, high wind velocity and low humidity due to excess loss
by evaporation. In such regions drip or trickle irrigation is most suitable.
This method was first developed by Israel and is rapidly gaining
importance all over the world.
• This method consist of carrying the irrigation water through pipe and
water is allowed to drip or trickle in the root zone of the crop under low
pressure.
• Two different pipes are used in this method. A perforated plastic pipe is
laid along the ground at the base of a row of crops or plants. The
perforation are designed are designed to emit a trickle and spaced to
produce a wetted strip along the crop row.
• In the second system, Irrigation water is conveyed through a larger feeder
pipe below the ground and is allowed to drip at the root zone of the crop
slowly through nozzle or orifice practically at low pressure. Thus root
zone is kept constantly wet.
29. Components of Drip Irrigation
• A pump to lift water from source to overhead tank.
• An overhead tank to store water to maintain a pressure head of 5
m to 7 m.
• Centeral distribution system comprising fertilizer tank, filter and
water regulator.
• Main and secondary pipes made of P.V.C. diameter may vary
from 2 cm to 4 cm depending on water to be supplied.
• Trickle lines consists of 1 cm to 2 cm diameter with perforation
where nozzles are fitted.
• Plastic nozzles having perforation are attached to laterals.
• Size of overhead tank and pipes depend on requirement of water
in the crop field. The spacing between laterals and nozzle is
governed by type of crop. Growth stage of crop, type of soil,
interval of crop row and agro-technical practices.
32. Advantages of Drip Irrigation
• Excellent control of water is possible as water is possible as
water can be applied at the rate to the consumptive use of
water.
• Evaporation from soil is reduced to minimum.
• Deep percolation of water is entirely eliminated.
• Nutrients can be applied directly to plant roots by adding
liquid fertilizers to the water.
• Salinity problems does not arise.
• Although initial cost is high, maintenance and labor may
be low once the system is set up.
• It is best method to reclaim desert areas
• It is not affected by the action of wind
• Soil erosion and tail water loss do not take place.
33. Advantages of Drip Irrigation
• Weed growth control is possible.
• It can be used for uneven topography.
• Less requirement of water as loss is minimum.
• Insect and pest control chemicals can be directly applied to
the root zone
• Weed growth control is possible.
• It can be used for uneven topography.
• Less requirement of water as loss is minimum
• No over irrigation takes place.
• Method is specially suitable for cash crop like vegetables,
fruits tobacco, cotton, etc..
• Due to control supply, water logging is avoided.
34. Dis-Advantages of Drip Irrigation
• Application of insoluble fertilizers like super-sulphonate,
etc., is not possible readily through flow system.
• Heavy rainfall may push downward the accumulated salts
at the edge of wetted zone. This may affect the crop growth
if this salt comes to the root zone.
• Dripper or nozzles blockages is likely to occur by soil
particles, as the size of nozzle varies from 0.5 to 2 mm.
• Due to high initial cost, farmers normally do not prefer this
method
• It is only suitable for close growing crops like vegetables,
etc..
• Frequent change of trickle lines are necessary as spacing of
nozzle is different for types of crops.
35. Sub-Surface Method
• In this method, the water is applied to the root
zone of the crops by underground network of
pipes. The network consists of main pipe, sub-
main pipes, and lateral perforated pipes. The
perforated pipes allow the water to drip out
slowly and thus the soil below the root zone of
the crops absorbs water continuously. This
method is suitable for permeable soil like sandy
soil. The method is also known as drip method or
trickle method of irrigation.
37. Irrigation Channels
• Alignment of Canal.
• Canals are aligned on contour, ridge and along side
slope and they are named as:
• (i) Contour Canal
• (ii) Ridge or Watershed Canal
• (iii) Side Slope Canal
• In aligning irrigation canal the following important
points are to be considered:
• (i) It must cover the entire area proposed to be irrigated.
• (ii) Smallest possible length of the canal for economy,
smaller head loss due to friction and smaller loss in
seepage and evaporation.
38. Contour Canal
• Canal aligned nearly parallel to the contour is called Contour Canal.
• In contour canal, culturable area lies on one side of it. Thus, contour canal
can irrigate on one side. As one of the bank is on the higher side, so only a
bank is required to construct on the lower side. Therefore, it is sometimes
called single bank canal.
• Drawbacks
• Drainage enters from hilly side, so it has the risk of breaching and silting.
• It involves crossing the natural drainage and therefore, costly Cross
Drainage Works (CDWs) are required to be constructed.
• It can irrigate on one side only.
• Advantages
• Low Initial cost of construction as no need to construct one of the bank.
• Discharge capacity increases as rain water from higher side is collected in
the canal.
40. Ridge or Watershed Canal
• The canal is aligned along a natural watershed, known
as ridge. These canals usually take off from the
contour canal. It irrigates on both sides. C.D can be
avoided and hence it is more economical.
• Advantages
• This canal can supply water on both sides and thus a
large area may be taken under cultivation.
• As it flows along the highest line, it does not require to
cross natural drainage on its way. Therefore, costly
Cross Drainage works (CDWs) are not at all necessary.
• It is the best irrigation canal and most economical.
41. Ridge or Watershed Canal
• Dis-Advantages
• If watershed has number of sharp loops, certain
problems are encountered.
• Aligning canal along the ridge, length becomes
more and if length are reduced aligning straight,
high ground left between canal and the ridge
line, cannot be irrigated. Moreover, CDWs are
required to construct as drainage may flow from
high land. If villages or towns are situated on
ridge, canal has to leave the ridge to bypass the
town and villages.
43. Side-Slope Canal
• This canal is aligned roughly perpendicular to contour
of the contour. Since it is perpendicular to the contour,
construction of Cross Drainage Works (CDWs) does
not arise. Since constructed along the falling contour,
slope of this canal is steep, which is not essential for
unlined canal. It irrigates only on one side just like
contour canal.
• Advantages:
• Construction of CDWs is not necessary
• Disadvantages:
• Slope of this channel is more. If it is unlined erosion
takes place. It also irrigates one side of the canal.
45. Water-Logging
• In agricultural land, when the soil pores
within the root zone of the crops gets
saturated with the subsoil water, the air
circulation within the soil pores gets totally
stopped. This phenomenon is termed as water
logging.
• The water logging makes the soil alkaline in
character and the fertility of land is totally
destroyed and the yield of the crop is reduced.
47. Causes of Water-Logging
• The following are the main cause of water
logging:
• (i) Over Irrigation: In inundation irrigation
since there is no controlling system of water
supply it may cause over irrigation. The
excess water percolates and remains stored
within the root zone of the crops. Again, in
perennial irrigation system if water is applied
more than what is required than this excess of
water is responsible for water logging.
48. Causes of Water-Logging
• Seepage from Canals:
• In Unlined canal systems, the water percolates
through the bank of the canal and gets
collected in the low lying areas along the
course of the canal and thus the water table
gets raised. This seepage is more in case of
canal in banking
49. Causes of Water-Logging
• Inadequate Surface Drainage:
• When the rainfall is heavy and there is no proper
provision for surface drainage the water gets
collected and submerges vast area. When the
condition continuous for a long period, the water
table is raised.
• Obstruction in Natural Water Course:
• If the bridges or culverts are constructed across with
the opening with insufficient discharges capacity,
the upstream area gets flooded and this causes water
logging.
50. Causes of Water-Logging
• Obstruction in Sub-Soil Drainage:
• If some impermeable stratum exists at a lower
depth below the ground surface, then the
movement of the subsoil water gets obstructed
and this cause water logging in the area.
• Nature of Soil:
• The soil having low permeability, like black
cotton soil, does not allow the water to percolate
through it. So, in case of over irrigation or flood,
the water retains in this type of land and cause
water logging.
51. Causes of Water-Logging
• Incorrect method of Cultivation:
• If the agriculture land is not levelled properly and there
is no arrangement for the surplus water to flow out, then
it will create pools of stagnant water leading to water
logging.
• Seepage from Reservoir:
• If the reservoir basin consists of permeable zones, cracks
and fissures which were not detected during the
construction of dam, these may cause seepage of water.
This sub-soil water will move forward toward the low
lying area and cause water logging.
52. Causes of Water-Logging
• Poor Irrigation Management:
• If the main canal is kept open for a long period
unnecessarily without computing the total water
requirement of the crops, then this leads to over
irrigation, which shall result in water logging.
• Excessive Rainfall:
• If the rainfall is excessive and the water gets no time
to get drained off completely, then a pool of stagnant
water is formed which might lead to water logging.
53. Causes of Water-Logging
• Topography of the land:
• If the agricultural land is flat, i.e. with no country
slope and consists of depression or undulations, then
this leads to water logging.
• Occasional Flood:
• If an area gets affected by flood every year and there
is no proper drainage system, the water table gets
affected and this cause water logging.
55. Adverse Effects of Water-Logging
• The following are the adverse effects of water logging:
• (i) Salination of Soil:
• Due to water logging the dissolved salts like sodium
carbonate, sodium chloride and sodium sulphate come
to the surface of soil. When the water evaporates from
the surface, the salts are deposited there. This process
is known as salinization of soil. Excessive
concentration of salts make the land alkaline. It does
not allow the plants to thrive and thus the yield of
crop is reduced. This process is also known as salt
efflorescence
56. Adverse Effects of Water-Logging
• Lack of Aeration:
• The crops require some nutrients for their growth
which are supplied by some bacteria or micro-
organisms by breaking the complex nitrogenous
compound into simple compound which are
consumed by the plants for their growth. But the
bacteria requires oxygen for their life and activity.
When the aeration in the soil is stopped by water
logging, these bacteria cannot survive without oxygen
and the fertility of the land is lost which results in
reduction of yield.
57. Adverse Effects of Water-Logging
• Fall of Soil Temperature:
• Due to the water logging the soil temperature is
lowered. At low temperature of the soil the activity of
the bacteria becomes very slow and consequently the
plants do not get the requisite amount of food in time.
Thus the growth of the plants is hampered and the
yield also is reduced.
• Growth of weeds and aquatic plants:
• Due to water logging, the agricultural land is
converted to marshy lands and the weeds and aquatic
plants grow in plenty. These plants consume the soil
foods in advance and thus the crops are destroyed.
58. Adverse Effects of Water-Logging
• Diseases of Crops:
• Due to low temperature and poor aeration, the crops
get some diseases which may destroy the crops or
reduce the yields.
• Difficulty in Cultivation:
• In water logged area it is very difficult to carry out the
operation of cultivation such as tilling, ploughing. etc.
• Restriction of Root Growth:
• When the water table rises near the root zone the soil
gets saturated. The growth of the roots is confined only
to the top layer of the soil. So, the crop cannot be
matured properly and the yield is reduced.
60. Control of Water Logging
• The following measures may be taken to control
water logging:
• (i) Prevention of percolation from Canals:
• The irrigation canals should be lined with
impervious lining to prevent the percolation of
water through the bed and banks of the canals.
Thus the water logging may be prevented.
• Intercepting drains may be provided along the
course of the irrigation canals in place where the
percolation of water is detected. The percolation
water is intercepted by the drains and the water
is carried to other natural water course.
62. Control of Water Logging
• Prevention of percolation from the reservoirs:
• During the construction of dams, the geological
survey should be conducted on the reservoir
basin to detect the zone of permeable formations
through which water may percolate. These zones
should be treated properly to prevent seepage, If
afterwards it is found that there is still leakage of
water through some zone, then sheet piling
should be done to prevent the leakage.
63. Control of Water Logging
• Control of Intensity of Irrigation:
• The intensity of irrigation may cause water logging so,
it should be controlled in a planned way so that there
is no possibility of water logging in a particular area.
• Economic Use of Water:
• If the water is used economically, then it may control
the waterlogging and the yield of the crop may be
high. So, Special training is required to be given to the
cultivators to realize the benefits of economical use of
water. It helps them to get more crops by eliminating
the possibility of water logging.
64. Control of Water Logging
• Fixing of Crop Pattern: Soil survey should be
conducted to fix the crop pattern. The crops
having high rate of evapotranspiration should be
recommended for the area susceptible to water
logging.
• Providing Drainage System:
• Suitable drainage system should be provided in
the low lying area so that rain water does not
stand for long days. A network of sub-surface
drains are provided which are connected to the
surface drains. The surface drains discharge the
water to the river or any water course.
65. Control of Water Logging
• Improvement of Natural Drainage:
• Sometimes, the natural drainage may be completely silted up or
obstructed by weeds, aquatic plants, etc. The affected section of the
drainage should be improved by excavating and clearing the
obstruction.
• Pumping of Ground water:
• A number of open well or tube wells are constructed in the water
logged area and the ground water is pumped out until the goes
down to a safe level. The lifted ground water may be utilized for
irrigation or may be discharged to the river or any water course.
• Construction of Sump Well:
• Sump Well may be constructed within the water logged area and
they help to collect the surface water. The water from the sump
well may be pumped to the irrigable lands or may be discharged to
any river.
68. Canal Lining
• Object of Canal Lining:
• (a) To Control Seepage:
• The seepage loss is the maximum loss in unlined
canals. Due to seepage. Due to seepage the duty of
canal is much reduced which involves enhancement
of storage capacity of a reservoir by constructing
high dam. Thus, the expenditure of the project is
increased. So to control the seepage loss through the
bed and sides of the canal, the lining of the canal is
necessary.
70. Canal Lining
• (b) To prevent Water-Logging
• Along the course of the canal, there may be low
lying areas on one side or both sides of the canal.
Due to the seepage of water through the sides of
the sides of the canal, these areas may get
converted into marshy lands. This water-logging
makes the land alkaline which is unsuitable for
agricultural. This water-logging area may
become the breeding place of mosquitos which
are responsible for many infectious diseases.
72. Canal Lining
( c) To increase the capacity of canal.
In unlined canal, the velocity of flow should be fixed
such that the silting and scouring is avoided. In Practice,
the velocity should always be kept below 1 m/s. Due to
the low velocity, the discharge capacity of the canal
becomes low. In unlined canal, if the capacity of the
canal is to be increased the cross-sectional area has to be
increased which involve more land width. So, the lining
of the canal should be such that the velocity and the
discharge of the canal are more with minimum cross-
sectional area.
73. Canal Lining
(d) To increase the command Area.
If the lining is provided in the canals the various
losses can be controlled and ultimately the
command area of the project may be enhanced.
74. Canal Lining
• (e) To Protect the Canal from the Damage by Flood The
unlined canals may be severely damaged by scouring and
erosion caused due to the high velocity of flood water at
the time of heavy rainfall. So, to protect the canals from the
damage, the lining should be provided.
• (f) To control the growth of weeds : the growth of various
types of weeds along the sides of the canals is a common
problem. Again, some type of weeds are found to grow
along the bed of the canals. These weeds reduce the
velocity of flow and the capacity of the canals. So, the
unlined canals require excessive maintenance works for
clearing the weeds. If lining is provided in the canal, the
growth of weeds can be stopped and velocity and the
capacity of the canal may be increased.
75. Advantages and Disadvantages of
Canal Lining
• Advantages:
• It reduces the loss of water due to seepage and hence the duty
is enhanced.
• It controls the water logging and hence the bad effects of
water logging.
• It provides smooth surface and hence the velocity of flow can
be increased.
• Due to the increased velocity the discharge capacity of a
canal is also increased.
• Due to the increased velocity , the evaporation loss also be
reduced.
• It eliminates the effect of scouring the canal bed.
76. Advantages
• The increased velocity eliminates the possibility
of silting of the canal bed.
• It control the weeds along the canal side and
bed.
• It reduces the requirement of land width for the
canal, because smaller section of the canal can
produce greater discharge.
• It prevents the sub-soil salt to come in contact
with canal water.
• It reduces the maintenance cost of canals.
77. Advantages and Disadvantages of
Canal Lining
• Disadvantages
• The initial cost of canal lining is very high. So, it
makes the project very expensive with respect to
the output.
• It involves much difficulties for repairing the
damage section of lining.
• It takes too much time to complete the project
work.
• It becomes difficult, if the outlet are required to
be shifted or new outlets are required to be
provided, because the dismantling of the lined
section is difficult.
78. Land Reclamation
• The reclamation of land is the process of making a land culturable
after it gets converted to uncultivable area due to the bad effect of
water logging. The following are the general methods of land
reclamation.
• (i) Leaching
• Leaching is a process for reclamation of the saline soil. In this
process, the agricultural land is flooded with water to a depth of
about 20-30 cm. the salt deposited on the surface are dissolved.
Some portion of salt is then drained off through the subsoil
drainage system and some portion of salt is then drained off
through the subsoil drainage system and some portion is removed
by surface drainage system. This operation is repeated several times
at specific intervals
• Generally, Leaching is followed by crop rotation as recommended
by agricultural department.
79. Land Reclamation
• Addition of Chemical Agent
• For improving he alkaline soil a chemical like gypsum is
generally added with irrigation water. The gypsum
neutralizes the alkaline effect of the soil and yield of the
crop is increased.
• Surface Drainage
• Proper surface drainage system should be provided in
the agricultural land so that the water does not
accumulates for a long time. The surface drains also help
in draining the saline water in case of leaching
operation.
80. Land Reclamation
• Sub-Surface Drainage
• The sub-surface drainage system on the
agricultural land should also be provided for
draining the excess water from the root zone. It
also helps in draining of saline water in case of
leaching operation.
• Additional of Waste Products
• Waste products like ground nut shells, saw dust,
etc. are added to the alkaline soil and these are
very effective in removing the salinity of soil.
81. Land Reclamation
• Excavation of ponds
• Ponds are excavated at suitable places within the
water logged area. The excess run-off is collected
in the ponds. The pore water also flows towards
the pond and thus the saturation in the root zone
of the crop is reduced. In fact, these ponds
control the water logging in rainy season and in
dry season the water of the pond may be used for
lift irrigation
82. Land Reclamation
• Pumping of Water from Tube Wells
• Some tube wells are sunk within the water
logged area. The water is pumped
continuously from the tube wells, Initially this
water is discharged to a river or pond.
• When the reclamation of the land is complete,
the water may be utilized for lift irrigation.
