Methods of Irrigation

Module-IIPart-I

Module-II• Methods of Irrigation:• Classification- choice of method of irrigation- surface

and subsurface irrigation methods, Sprinkler and DripIrrigation

• Irrigation channels:• Alignment- canal capacity- losses- FSL of canal-

design of canal in alluvial soil and non alluvialsoils- Kennedy’s silt theory- Lacey’s regime theory-balancing depth- use of Garrets diagrams and Lacey’sRegime diagrams- lining of irrigation channels-design of lined canal- drainage behind lining. Waterlogging: Causes, Measures: surface and sub-surfacedrains, land reclamation

Methods of Water Distribution to Crop Fields

• The chapter deals with the different methodsof water distribution to the crops like furrowmethod, contour farming, flooding method,boarder strips, contour laterals, sprinklerirrigation and drip irrigation methods.

Surface Irrigation Method• Furrow Method• In this method, irrigation water is useful for row

crops. Narrow channels are dug at regularintervals. Water from the main supply is allowedto enter these small channels or furrows. Waterfrom the furrows infiltrates into soil and spreadlaterally to saturate the root zone of the crops. Itis suitable for row crops like potatoes, sugarcane,tobacco, maize, groundnut, cotton, jowar, etc..

Furrow Method

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.

Furrow Method

Contour Farming• Contour farming is practiced in hilly areas

with slopes and with falling contour. The landis divided into series of horizontal strips calledterraces. Small bunds are constructed at theend of each terrace to hold water up to equalheight. Contour farming besides producingcrop yields, helps in mitigating indirectlycontrolling flood, soil conservation.

Contour Farming

Contour Farming

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 areprovided with the field regulator. This method isknown as irrigation by plots commonly used inIndia.

• In this method when the strips are flooded withwater, surplus water is allowed to enter thewater channel and allowed to discharge in thewater downstream.

Flooding Method

Basin Flooding• This method is used frequently to irrigate the

orchards. It is a special type of check floodingmethod. Each plant is enclosed by circularchannels which is called basin. Basins areconnected to small field ditches.

• Ditches are fed from the main supply channel.When the basin are flooded, the supply isstopped. Portable pipes or large hoses may alsobe used in place of ditches to flood the basin

Basin Flooding

Basin Flooding

Check Flooding• In check flooding the crop area is divided into

some plots which are relatively leveled bychecks or bunds water from field channels isallowed to enter to each plot or check basinand the plots are flooded to the requireddepth.

Check Flooding

Border Strips• In this method, the agricultural area is divided into

series of long narrow strips known as border stripsby levees, i.e. small bunds. The strips are alignedalong the country slope so that the water can floweasily throughout the area. This method is suitablewhen the area is at level with gentle country slope.

Border Strips

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 plotsfrom the field channel through the openings.The water flows in a zig-zag way to cover theentire area. When the desired depth isattained, the openings are closed.

Sprinkler Irrigation Method• In this method, water is applied to the crop in the form

of sprinkle or spray with the combination of pump, mainpipe, sub-main pipe, lateral, riser, nozzle, etc..

• It is a kind of artificial rainfall and therefore, it is veryfruitful 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.

Sprinkler Irrigation Method

Sprinkler Irrigation Method

Sprinkler Irrigation Method

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

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.

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 lossby evaporation. In such regions drip or trickle irrigation is most suitable.This method was first developed by Israel and is rapidly gainingimportance all over the world.

• This method consist of carrying the irrigation water through pipe andwater is allowed to drip or trickle in the root zone of the crop under lowpressure.

• Two different pipes are used in this method. A perforated plastic pipe islaid along the ground at the base of a row of crops or plants. Theperforation are designed are designed to emit a trickle and spaced toproduce a wetted strip along the crop row.

• In the second system, Irrigation water is conveyed through a larger feederpipe below the ground and is allowed to drip at the root zone of the cropslowly through nozzle or orifice practically at low pressure. Thus rootzone is kept constantly wet.

Drip or Trickle Irrigation

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 isgoverned by type of crop. Growth stage of crop, type of soil,interval of crop row and agro-technical practices.

Components of Drip Irrigation

Components of Drip Irrigation

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 ofwater.

• 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.

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.

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 saltsat the edge of wetted zone. This may affect the crop growthif this salt comes to the root zone.

• Dripper or nozzles blockages is likely to occur by soilparticles, as the size of nozzle varies from 0.5 to 2 mm.

• Due to high initial cost, farmers normally do not prefer thismethod

• It is only suitable for close growing crops like vegetables,etc..

• Frequent change of trickle lines are necessary as spacing ofnozzle is different for types of crops.

Sub-Surface Method• In this method, the water is applied to the root

zone of the crops by underground network ofpipes. The network consists of main pipe, sub-main pipes, and lateral perforated pipes. Theperforated pipes allow the water to drip outslowly and thus the soil below the root zone ofthe crops absorbs water continuously. Thismethod is suitable for permeable soil like sandysoil. The method is also known as drip method ortrickle method of irrigation.

Sub-Surface Method

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 inseepage and evaporation.

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 abank is required to construct on the lower side. Therefore, it is sometimescalled 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.

Contour Canal

Ridge or Watershed Canal• The canal is aligned along a natural watershed, known

as ridge. These canals usually take off from thecontour canal. It irrigates on both sides. C.D can beavoided 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, costlyCross Drainage works (CDWs) are not at all necessary.

• It is the best irrigation canal and most economical.

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 ridgeline, cannot be irrigated. Moreover, CDWs arerequired to construct as drainage may flow fromhigh land. If villages or towns are situated onridge, canal has to leave the ridge to bypass thetown and villages.

Ridge or Watershed Canal

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) doesnot arise. Since constructed along the falling contour,slope of this canal is steep, which is not essential forunlined canal. It irrigates only on one side just likecontour 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.

Side-Slope Canal

Water-Logging• In agricultural land, when the soil pores

within the root zone of the crops getssaturated with the subsoil water, the aircirculation within the soil pores gets totallystopped. This phenomenon is termed as waterlogging.

• The water logging makes the soil alkaline incharacter and the fertility of land is totallydestroyed and the yield of the crop is reduced.

Water-Logging

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 watersupply it may cause over irrigation. Theexcess water percolates and remains storedwithin the root zone of the crops. Again, inperennial irrigation system if water is appliedmore than what is required than this excess ofwater is responsible for water logging.

Causes of Water-Logging• Seepage from Canals:• In Unlined canal systems, the water percolates

through the bank of the canal and getscollected in the low lying areas along thecourse of the canal and thus the water tablegets raised. This seepage is more in case ofcanal in banking

Causes of Water-Logging• Inadequate Surface Drainage:• When the rainfall is heavy and there is no proper

provision for surface drainage the water getscollected and submerges vast area. When thecondition continuous for a long period, the watertable 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 waterlogging.

Causes of Water-Logging• Obstruction in Sub-Soil Drainage:• If some impermeable stratum exists at a lower

depth below the ground surface, then themovement of the subsoil water gets obstructedand 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 percolatethrough it. So, in case of over irrigation or flood,the water retains in this type of land and causewater logging.

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, thenit will create pools of stagnant water leading to waterlogging.

• Seepage from Reservoir:• If the reservoir basin consists of permeable zones, cracks

and fissures which were not detected during theconstruction of dam, these may cause seepage of water.This sub-soil water will move forward toward the lowlying area and cause water logging.

Causes of Water-Logging• Poor Irrigation Management:• If the main canal is kept open for a long period

unnecessarily without computing the total waterrequirement of the crops, then this leads to overirrigation, 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 stagnantwater is formed which might lead to water logging.

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, thenthis 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 getsaffected and this cause water logging.

Causes of Water-Logging

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 cometo the surface of soil. When the water evaporates fromthe surface, the salts are deposited there. This processis known as salinization of soil. Excessiveconcentration of salts make the land alkaline. It doesnot allow the plants to thrive and thus the yield ofcrop is reduced. This process is also known as saltefflorescence

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 nitrogenouscompound into simple compound which areconsumed by the plants for their growth. But thebacteria requires oxygen for their life and activity.When the aeration in the soil is stopped by waterlogging, these bacteria cannot survive without oxygenand the fertility of the land is lost which results inreduction of yield.

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 ofthe bacteria becomes very slow and consequently theplants do not get the requisite amount of food in time.Thus the growth of the plants is hampered and theyield 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 aquaticplants grow in plenty. These plants consume the soilfoods in advance and thus the crops are destroyed.

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 orreduce 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 onlyto the top layer of the soil. So, the crop cannot bematured properly and the yield is reduced.

Adverse Effects of Water-Logging

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 ofwater through the bed and banks of the canals.Thus the water logging may be prevented.

• Intercepting drains may be provided along thecourse of the irrigation canals in place where thepercolation of water is detected. The percolationwater is intercepted by the drains and the wateris carried to other natural water course.

Remedial Measures: Against Water-Logging

Tile Drain Canal Lining

Control of Water Logging• Prevention of percolation from the reservoirs:• During the construction of dams, the geological

survey should be conducted on the reservoirbasin to detect the zone of permeable formationsthrough which water may percolate. These zonesshould be treated properly to prevent seepage, Ifafterwards it is found that there is still leakage ofwater through some zone, then sheet pilingshould be done to prevent the leakage.

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 thereis 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 behigh. So, Special training is required to be given to thecultivators to realize the benefits of economical use ofwater. It helps them to get more crops by eliminatingthe possibility of water logging.

Control of Water Logging• Fixing of Crop Pattern: Soil survey should be

conducted to fix the crop pattern. The cropshaving high rate of evapotranspiration should berecommended for the area susceptible to waterlogging.

• Providing Drainage System:• Suitable drainage system should be provided in

the low lying area so that rain water does notstand for long days. A network of sub-surfacedrains are provided which are connected to thesurface drains. The surface drains discharge thewater to the river or any water course.

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 thedrainage should be improved by excavating and clearing theobstruction.

• 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 goesdown to a safe level. The lifted ground water may be utilized forirrigation 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 sumpwell may be pumped to the irrigable lands or may be discharged toany river.

Remedial Measures: Against Water-Logging

Leaching of Saline Soil

Crop Rotation

Remedial Measures: Against Water-Logging

Optimum Use of Water

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 ofcanal is much reduced which involves enhancementof storage capacity of a reservoir by constructinghigh dam. Thus, the expenditure of the project isincreased. So to control the seepage loss through thebed and sides of the canal, the lining of the canal isnecessary.

Canal Lining

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 ofthe sides of the canal, these areas may getconverted into marshy lands. This water-loggingmakes the land alkaline which is unsuitable foragricultural. This water-logging area maybecome the breeding place of mosquitos whichare responsible for many infectious diseases.

Canal Lining

Canal Lining( c) To increase the capacity of canal.In unlined canal, the velocity of flow should be fixedsuch that the silting and scouring is avoided. In Practice,the velocity should always be kept below 1 m/s. Due tothe low velocity, the discharge capacity of the canalbecomes low. In unlined canal, if the capacity of thecanal is to be increased the cross-sectional area has to beincreased which involve more land width. So, the liningof the canal should be such that the velocity and thedischarge of the canal are more with minimum cross-sectional area.

Canal Lining(d) To increase the command Area.If the lining is provided in the canals the variouslosses can be controlled and ultimately thecommand area of the project may be enhanced.

Canal Lining• (e) To Protect the Canal from the Damage by Flood The

unlined canals may be severely damaged by scouring anderosion caused due to the high velocity of flood water atthe time of heavy rainfall. So, to protect the canals from thedamage, the lining should be provided.

• (f) To control the growth of weeds : the growth of varioustypes of weeds along the sides of the canals is a commonproblem. Again, some type of weeds are found to growalong the bed of the canals. These weeds reduce thevelocity of flow and the capacity of the canals. So, theunlined canals require excessive maintenance works forclearing the weeds. If lining is provided in the canal, thegrowth of weeds can be stopped and velocity and thecapacity of the canal may be increased.

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.

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 canproduce greater discharge.

• It prevents the sub-soil salt to come in contactwith canal water.

• It reduces the maintenance cost of canals.

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 tothe output.

• It involves much difficulties for repairing thedamage section of lining.

• It takes too much time to complete the projectwork.

• It becomes difficult, if the outlet are required tobe shifted or new outlets are required to beprovided, because the dismantling of the linedsection is difficult.

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 ofwater logging. The following are the general methods of landreclamation.

• (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 ofabout 20-30 cm. the salt deposited on the surface are dissolved.Some portion of salt is then drained off through the subsoildrainage system and some portion of salt is then drained offthrough the subsoil drainage system and some portion is removedby surface drainage system. This operation is repeated several timesat specific intervals

• Generally, Leaching is followed by crop rotation as recommendedby agricultural department.

Land Reclamation• Addition of Chemical Agent• For improving he alkaline soil a chemical like gypsum is

generally added with irrigation water. The gypsumneutralizes the alkaline effect of the soil and yield of thecrop is increased.

• Surface Drainage• Proper surface drainage system should be provided in

the agricultural land so that the water does notaccumulates for a long time. The surface drains also helpin draining the saline water in case of leachingoperation.

Land Reclamation• Sub-Surface Drainage• The sub-surface drainage system on the

agricultural land should also be provided fordraining the excess water from the root zone. Italso helps in draining of saline water in case ofleaching operation.

• Additional of Waste Products• Waste products like ground nut shells, saw dust,

etc. are added to the alkaline soil and these arevery effective in removing the salinity of soil.

Land Reclamation• Excavation of ponds• Ponds are excavated at suitable places within the

water logged area. The excess run-off is collectedin the ponds. The pore water also flows towardsthe pond and thus the saturation in the root zoneof the crop is reduced. In fact, these pondscontrol the water logging in rainy season and indry season the water of the pond may be used forlift irrigation

Land Reclamation• Pumping of Water from Tube Wells• Some tube wells are sunk within the water

logged area. The water is pumpedcontinuously from the tube wells, Initially thiswater is discharged to a river or pond.

• When the reclamation of the land is complete,the water may be utilized for lift irrigation.

ThanksGHT