Lec 9 Border irrigation – Design and hydraulics.ppt

Border irrigation

1. Border irrigation –Design and
hydraulics

2. Borderirrigation
•Thebordermethodofirrigationmakesuseofparallelridgestoguideasheetof
flowingwaterasitmovesdowntheslope.Thelandisdividedintoanumberof
longparallelstripscalledbordersthatareseparatedbylowridges.Theborder
striphaslittleornocrossslopebuthasauniformgentleslopeinthedirectionof
irrigation.

4. •Eachstripisirrigatedindependentlybyturninginastreamofwaterattheupper
end.Thewaterspreadsandflowsdownthestripinasheetconfinedbytheborder
ridges.Whentheadvancingwaterfrontreachesthelowerend,afewminutes
beforeorafterthatthestreamisturnedoff.Thewatertemporarilystoredinthe
bordermovesdownthestripandinfiltrates,thuscompletingtheirrigation.
Bordersareoftwotypes:
•(i)Openendbordersand(ii)Blockedendborders
•Borderirrigationmethodissuitabletosoilshavingmoderatelylowtomoderately
highinfiltrationrates.Usuallyitisnotusedincoarsesandysoilsthathavevery
highinfiltrationrates.Thesizeofirrigationstreamperunitwidthofborderstrip
mustbelargerascomparedtoothermethodsofsurfaceirrigation.
•Thebordermethodissuitabletoirrigateallclosegrowingcropslikewheat,barley,
foddercropsandlegumes.Itishowever,notsuitableforcropslikerice.

5. Advantages of border irrigation
•Border ridges can be constructed economically with simple farm implements like a
bullock drawn A-frame ridger or bund former or tractor drawn disc ridger.
•Labour requirement in irrigation is reduced as compared to check basin method of
irrigation.
•Uniform distribution and high water application efficiencies are possible if the
system is properly designed.
•Large irrigation streams can be efficiently used
•Operation of the system is simple and easy

6. Borderspecificationsandstreamsize
Properdesignrequiresconsiderationofthehydraulicsofflowinborders
Widthofborderstrip:
Thewidthofborderusuallyvariesfrom3to15metresdependingonthesizeofthe
irrigationsystemavailable.
Borderlength
Thelengthoftheborderstripdependsuponhowquicklyitcanbewetteduniformly
overitsentirelength.Thisinturndependsontheinfiltrationrateofthesoil,the
slopeofthelandandthesizeoftheirrigationstreamavailable.
Sandy and sandy loam soils:60 to 120 metres
Medium loam soil :100 to 180 metres
Clay loam and clay soil :150 to 300 metres

7. Borderslope:
Thebordersshouldhaveauniformlongitudinalgradient.
Sizeofirrigationstream
Coarsetexturedsoilswithhighinfiltrationratesrequirelargestreamstospreadwater
overtheentirestriprapidlyandavoidexcessivelossesduetodeeppercolationat
theupperreaches.Finetexturedsoilswithlowinfiltrationratesrequiresmaller
streamstoavoidexcessivelosesduetorunoffatthedownstreamendanddeep
percolationatthelowerreaches.
Itisconvenienttoexpresstherequirementoftheirrigationstreamintermsoftherate
ofwaterflowperunitwidthofthebordersuchasinlitrespersecondpermetreof
borderwidth.
Sandyloamtosandysoils:0.25%to0.60%
Mediumloamsoil :0.20%to0.40%
Claytoclayloamsoil:0.05%to0.20%

8. Hydraulics of border irrigation:
The flow in a border strip is a case of spatially varied unsteady open channel flow
with decreasing discharge.The discharge rate decreases downstream due to
infiltration.
The dominant variables influencing border irrigation are –(i) size of irrigation stream,
(ii) slope of the land surface, (iii) infiltration characteristics of the soil and (iv) the
resistance to flow offered by the soil surface and vegetative cover.
A complete analysis of border irrigation would require information on the effect of
land slope, infiltration, roughness of soil surface, vegetation and depth of water on
the velocity of flow down the slope.

9. 9

10. Anyrationalapproachtopredictsurfaceirrigationflowsmustequatethetotalvolumeof
waterdischargedatthesupplychanneltothesumofsurfacestorageandsubsurface
storage,moreoverthisvolumebalanceisobtainedateveryinstantoftime,
subsequenttotheinitialturningofwaterontotheland.
Let,
q= constant rate of flow per unit width introduced at the upstream end of the border,
cm
2
/min. (i.e cm
3
/min/cm of border width)
t = total time for which irrigation water has been applied, min
x= distance the irrigation stream has advanced, cm
d = average depth of water over the ground surface, cm
ts = value of t at which x(t) = s, min
y(t-ts) = accumulated infiltration at the point x=s at time t
s, cm
s = value of x at t = ts, cm and
x’(t
s) = the value of stt
dt
dx
at

11. Referring to Fig.
•Total water admitted in time t per unit width = qt
•Volume of water stored on the ground surface per unit width = d.x
•Volume of water infiltrated into the soil = Applying the volume balance
relationship,

12. y is the function of (t-ts) and
x is a function of ts
………………. (1)
This equation was proposed by Lewis and Milne (1938)
Philip and Farrel(1964) using the Faltungor convolution theorem of Laplace transformation obtained the
general solution of equation as follows.
…………………….. (2)
This equation (2) represents the general solution of equation (1)
Field tests on infiltration at pre-sowing and post emergence irrigations indicate that the
functional relationship between accumulated infiltration and elapsed time can be
expressed best by the following empirical formula:
In which,
y = accumulated infiltration at time t, cm
t = elapsed time, minutes and
a, and b are characteristics constants

x
ydsxdqt
0
. 

t
sss
x
dttxttyyds
00
)(')( 









23
1 1
dsyLs
L
q
x baty 
 0,10  ta  

t
sss dttxttydxqt
0
)(')(

13. Recession flow
After the irrigation stream is cut off, the tail water recedes downstream. The rate of
recession of the tail water is determined by noting the times at which water just
disappears from the upstream end and recedes downstream past the border strip.
In plotting advance and recession curves, the distance down the border (or furrow) is
plotted on the x axis and the elapsed time on the y-axis. Both the advance and the
recession curves are plotted on the same graph (Fig.). Parallelism of advance and
recession curves ensures uniform distribution of water throughout the border.

14. Infiltration opportunity time (time of ponding)
Thedifferencebetweenthetimethewaterfrontreachesaparticularpointalongthe
border(orfurrow)andthetimeatwhichthetailwaterrecedesfromthesamepoint
istheinfiltrationopportunitytimeorthetimeofponding.Theinfiltration
opportunitytimeatanypointalongtheborder(orfurrow)istheverticaldistance(in
timescale)betweentheadvanceandrecessioncurvesatthepoint.

15. Designofborderirrigation:
Toobtainthemaximumwaterapplicationefficiencythewatershouldremainonthe
surfacesufficientlylongtoallowjustthedesiredamountofwatertoinfiltrateinto
thesoil.Therequiredinfiltrationopportunitytimeisobtainedusingthe
accumulatedinfiltrationtimerelationshipforthesoil.
Waterdistributionefficiencyisgovernedmainlybytheuniformityoftheinfiltration
opportunitytimeobtainedthroughouttheborderlength.Whenthebehaviorofthe
irrigationsystemcanbepredictedfromthemeasurablecharacteristicsofthesite,it
ispossibletoobtainanearlyuniforminfiltrationopportunitytimethroughoutthe
borderbysuitablyadjustingtheentrancestreamsize,andthelengthofrunorslope
oftheborder.

16. Procedure for efficient border irrigation system
(1) The length, width and slope of the border strip are determined
(2) The depth of water required to replenish the soil moisture in the root zone of the
crop to field capacity is estimated.
(3) The accumulated infiltration time relationship of the soil under the existing soil
conditions and vegetation is determined. The relationship can be established by
actual measurements with cylinder infiltrometers before each irrigation.
(4) The desired infiltration opportunity time is determined
(5) The hydraulic resistance is estimated on the basis of the soil surface roughness and
the hydraulic characteristics of the crop.
(6) The average depth of flow is estimated.
(7) The water front advance is predicted. The water front advance time relationship as a
function of the entrance stream sixe, average depth of flow and infiltration
characteristics.
(8) The irrigation system is designed to obtain the optimum water application efficiency
and border length.

17. Check Basin irrigation

18. Check basin
Bundsorridgesareconstructedaroundtheareasformingbasinswithinwhichthe
irrigationwatercanbecontrolled.
Design considerations
Water is conveyed to the field by a system of supply channels and lateral field channels. The
supply channel is aligned on the upper side of the area and there is usually one lateral for
every two rows of check basins. Water from the laterals is turned into the beds and is cut
off when sufficient water has been admitted to the basin. Water is retained in the basin
until it seeps into the soil.
Types of check basins, based on size and shape:
The size of the check basins may vary from 1 sq.m, used for growing vegetables to as large
as one or two hectares or more, used for growing rice under wetland conditions.
The vertical interval between contour ridges usually varies from 6 to 12 cm in case of upland
irrigated crops like wheat and 15 to 30 cm in case of lowland irrigated crops like rice.
Sandy and sandy loam soils with high infiltration rates permit only small size basins while clay
soils having low infiltration rates allow large basins.
In irrigating orchards, square or contour basins may be used. When the plants are widely
spaced, the ring method of basin irrigation may be adopted. The rings are circular basins
formed around each tree.

19. Adaptability:
Checkbasinirrigationissuitedforsmoothgentleanduniformlandslopesandfor
soilshavingmoderatetolowinfiltrationrates.
Checkbasinsareusefulwhenleachingisrequiredtoremovesaltsfromthesoil
profile.
Hydraulicsofcheckbasin:
Hydraulicsofflowincheckbasinsmaybeconsideredtocompriseoffourstages.
1.Initialspreadingoftheentrancestreamtocoverthefullwidthofthebasinand
simultaneousadvanceoftheirrigationstream.
2.Advanceofthewaterfrontaftertheinitialspreading
3.Riseofwaterlevelaftertheadvancingstreamreachesthedownstreamend,and
4.Subsidenceofwateraftertheirrigationstreamisstopped.

20. Essential difference between border irrigation and check basin irrigation:
The essential differences in the phenomenon are in the initial spreading of the entrance
stream to cover the full width of the basin and in the characteristics of the recession
flow.
(i) Spreading the entrance stream in a check basin:
The water front advance in a check basin differs from borders in the initial stages at the
upstream end of the basin. The entrance stream spreads on either side as it
advances forward till the entire width of the basin is covered. When the water is
introduced into a check basin from an orifice or other inlets, the flow is non-linear.
In non-linear flow, the paths of flow may diverge or converge along the flow line.
(ii) Water front advance in check basins:
The advance of the water front after the initial spreading in check basins is similar to
border irrigation method. The dominant variables are the same as in borders,
namely entrance stream size, infiltration characteristics of the soil, hydraulic
resistance offered by the soil surface and vegetation, water surface slope and
elapsed time.

21. (iii) Water storage and rate of rise in check basins:
Ponding occurs after the water front reaches the downstream end of the check basin.
The volume of storage above the soil surface in a given time period is equal to the
difference between the volume of water admitted into the basin during the period
and the volume infiltrated into the soil. This may be expressed as
In which
Vs = volume of water stored in a given time t
s, cm
3
q = average size of the entrance stream, cm
3
/min
t
s = storage time, min
I
s= average infiltration rate during the storage time, cm
3
/min
A
c= area of check basin, cm
2
and
d
s= depth of storage during t
s, cm scssss dAtIqtV 

22. (iv)Recessionofwaterincheckbasins
Recessioninacheckbasinmaybetakenasthesubsidenceofwaterduetoinfiltration.
Therecessionratecanbeestimatedwiththehelpoftheinfiltrationequation
Designofcheckbasinirrigationsystem:
Efficientirrigationbythecheckbasinmethoddependsontheknowledgeofthe
hydraulicsofflowinthebasin.Ausefulthumbruleincheckbasindesignisthat
thewaterspreadintheentirebasinshouldbecoveredinone-fourthofthetime
requiredtoinfiltratethenetdepthofirrigationwater.Thisisoftencalledthe
quartertimerule.
Quasi-rationaldesignsofcheckbasinsmaybedevelopedusingtheprocedure
suggestedbyborderirrigation

23. 23

25. Furrow irrigation
•Furrows are small, parallel channels made to carry water in order to irrigate the crop. The
crop is usually grown on the ridges between the furrows.

26. Cutbackstreaminfurrowirrigation
•Acommonmethodtoobtaintheoptimumopportunitytimetoapplyagiven
depthofirrigationinafurrowsystemistoallowtheinitialdesignstreamtoflow
thefulllengthofthefurrowandthenreducethestreamsizebyadjustingoutlet
gatesorbyreducingthenumberorsizeofspilesorsystemstopermitreduced
streamsize.Thefurrowstreaminsuchasituationiscalledthecutbackstream.
•Thesizeofthecutbackstreamisadjustedtomatchthecumulativeinfiltrationina
furrowsothatthereisnorunoffatthetailend.Theapplicationofthecutback
streamiscontinuedtillthetimerequiredtofillthecroprootzonetothefield
capacityofthesoil.

27. Advantages of furrow irrigation
•Water in the furrows contacts only one-half to one-fifth of the land surface therby
reducing puddling and crusting of the soil and evaporation losses
•Earlier cultivation is possible
•The method reduces labour requirements in land preparation and irrigation.
•Compared to check basin method, there is no wastage of land in field ditches.

28. •Furrows of 7.5 to 12.5 cm depth are appropriate for vegetable crops, while some
row crops and orchards require much deeper furrows.
•Furrows may be classified into two types based on their alignment. They are: (a)
straight furrows and (b) contour furrows
•Based on their size and spacings, furrows may be classified as deep furrows and
corrugations.
(a) Straight furrows:
•Straight furrows are laid down the prevailing land slpe. They are best suited to
sites where the land slope does not exceed 0.75 per cent.

29. (b)Contourfurrows
•Contourfurrowscarrywateracrossaslopingfieldratherthandowntheslope.Field
supplychannelsrundownthelandslopetofeedtheindividualfurrows.Contour
furrowmethodcanbesuccessfullyusedinnearlyallirrigablesoils.Thetopography
mustbeuniformenoughtopermitaheadditchthatcanfeedtheentireareaof
contourfurrows.
•Contourfurrowsmaybeusedonmostsoiltypes,exceptonlightsandysoilsand
soilsthatcrack.Theridgesbetweenfurrowsinsandysoilsmaybreakandwashout,
overloadingthefurrowbelow,whichalsobreaks.Thismaycontinuealltheway
downtheslopecausingheavyerosiondamage.Soilsthatcrackprovidechannelsfor
watercausingsimilardownslopefurrowbreaks.Hencecontourfurrowshaveonly
limiteduseonsteepslopesinsandysoilsandheavyblacksoils.
•Inheavyrainfallareasthelengthoffurrowsshouldbeshortenoughtodisposeoff
therunoffsafelywithoutbreakingthefurrows.Erosioncontrolstructuresare
neededtocarrythesurpluswaterdowntheslope.Contourfurrowirrigationusedin
conjunctionwithcontourbundingandterracingprovidesaninsuranceagainst
furrowbreaks.

30. Corrugationirrigation:
•Corrugationirrigationconsistsofrunningwaterinsmallfurrows,calledcorrugations
whichdirecttheflowdowntheslope.Itiscommonlyusedforirrigatingnon
cultivated,closegrowingcropssuchassmallgrainsandforpasturegrowingonsteep
slopes.Themainpointofdifferencefromregularfurrowirrigationisthatmore,but
smallerfurrowsareutilizedandthecroprowsarenotnecessarilyrelatedtothe
irrigationfurrows.
•Thecorrugationscanbemadewithasimplebamboocorrugatororcultivators
equippedwithsmallfurrowersorothersimilarimplements.
•CorrugationsareVshapedorUshapedchannelsabout6to10cmdeep,spaced40
to75cmapart.Theentiresoilsurfaceiswettedslowlybythecapillarymovementof
thewaterwhichflowsinthecorrugations.Corrugationirrigationismostsuitablein
loamysoilsinwhichthelateralmovementofwatertakesplacereadily.Claysoilswith
lowinfiltrationratesaredifficulttoirrigatebythismethod,unlesstheslopesare
quiteflat.Itisalsonotsuitableindeepsandysoilsbecauseoftheexcessivelossof
waterbydeeppercolation.
•Thecorrugationmethodisnotrecommendedonsalinesoilsorwhentheirrigation
waterhasahighsaltcontent.Thepermissiblelengthofcorrugationsvariesfrom
about50minlighttexturedsoilswithslopesof2%to4%toabout150minheavy
texturedsoilsupto2%slope.

31. Corrugation furrow irrigation methods

32. Furrowirrigationhydraulics:
•Theflowphenomenoninfurrowirrigationisacaseofunsteadyopenchannelflow
withdecreasingdischarge.Furrowirrigationhowever,differsfrombordersand
basinsinthepatternofwettingthesoil,becausethewaterwhichsoaksintothe
soilspreadslaterallytotheadjacentareas.
•Thedominantvariablesinfluencingtherateofflowinfurrowsaretheentrance
streamsize,infiltrationrate,sizeandshapeofwettedsectionoffurrow,furrow
slopeandhydraulicresistance.Thehydraulicresistancetoflowmaybeduetothe
combinedeffectoftheroughnessofferedbythewettedsurfaceofthefurrowand
theresistanceofferedbythecrop.
•Asinborders,thetimeofpondingorinfiltrationopportunitytimeinafurrow
shouldbethetimeperiodrequiredforthenetdepthofwatertoinfiltratesothat
thecroprootzoneisfilledtoitsfieldcapacity.Thetimeofpondingisdemarcated
bythedifferencebetweentheadvanceandrecessiontimesinthefurrow.

33. Evaluationoffurrowirrigation:
•Infiltrationofwaterintothefurrowisthemostimportantvariableaffectingthe
characteristicsofflowinfurrows.Theinfiltrationratesinfurrowsmaybe
determinedbythegravimetricmethod,byspeciallydesignedfurrowinfiltrometer
ormorecommonlybytheinflow-outflowmethod.
•Inthegravimetricmethodthedifferenceinmoisturecontentinthesoilbeforeand
afterirrigationisdeterminedbysoilsamplingandmoisturedetermination.Itistime
consumingasitinvolvessamplingatmanylocations.
•Thefurrowinfiltrometertechniquesconsistsofblockingthefurrowsattheirtwo
endssoastoassessthevolumestoragedifferenceinthefurrowinrelationtotime.
Theinstrumentincludesafloatmechanismandawaterstagerecorder.
•Theinflow-outflowmethod,alsoknownasvolumebalancemethod,isconsideredto
bethemostsatisfactoryonebecauseitgivestheaverageinfiltrationvalueby
compensatingvariouserrors,inherentinthefurrows,arisingoutofsoil
heterogeneity,furrowcrosssectionaldifference,cracksandpuddlingeffects.

34. Inflowoutflowmethod:
•Intheinflow-outflowmethod,thefurrowisdividedintoanumberofsectionsand
Parshallflumesorothersuitablewatermeasuringdevicesareinstalledateach
stationtomeasuretheflowrate.Thefurrowspacingismeasuredfromthecentre
ofthefurrowtothecentreoftheadjacentfurrow.Therateofadvanceofwaterin
thetestsectionandthedepthofflowatdifferentpointsatdefinitetimeintervals
aremeasured.Fromtheabovemeasurementsitispossibletoobtainthefurrow
crosssectionalareaandwettedperimeter.Theaveragevalueofthewetted
perimetermultipliedbythelengthofthetestsectionareagivesthewettedarea.
•Accumulatedinfiltration=Accumulatedinflow–Accumulatedstorage(volume)section test of area Wetted
(volume)on infiltrati dAccumulate
(depth)on infiltrati dAccumulate 

35. Furrow irrigation design considerations
•Efficientirrigationbythefurrowmethodisobtainedbyselectingproper
combinationsofspacing,lengthandslopeoffurrows,suitablesizeoftheirrigation
streamanddurationofwaterapplication.
Furrowspacing:
•Furrowsshouldbespacedcloseenoughtoensurethatwaterspreadstothesides
intotheridgeandtherootzoneofthecrop,toreplenishthesoilmoistureuniformly.
Thelateralmovementofwaterfromthefurrowinsoilswithuniformprofiles
dependsprimarilyuponthetextureofthesoilwithabroaderwettingpattern
occurringinclaysthaninsandysoils.Toobtaincompletewettingofsandysoilsto
depthsof1to1.5metresthefurrowsshouldnotbespacedmorethan50to60cm
apart.Inuniformclaysoilscompletewettingtothesamedepthmaybeobtained
withafurrowspacingofonemeterormore.
Furrowlength
•Properfurrowlengthdependslargelyonthehydraulicconductivityofthesoil.
Furrowsmustbeshorteronaporoussandysoilthanonatightclaysoil.Thelength
offurrowwhichcanbeefficientlyirrigatedmaybeasshortas45monsoilswhich
takeupwaterrapidlyorasmuchas300morlongeronsoilswithlowinfiltration
rates.Thelengthoffurrowmayoftenbelimitedbythesizeandshapeofthefield.

36. Suitablesoils
Furrowscanbeusedonmostsoiltypes.However,aswithallsurfaceirrigation
methods,verycoarsesandsarenotrecommendedaspercolationlossescanbe
high.Soilsthatcrusteasilyareespeciallysuitedtofurrowirrigationbecausethe
waterdoesnotflowovertheridge,andsothesoilinwhichtheplantsgrow
remainsfriable.
•Insandysoilswaterinfiltratesrapidly.Furrowsshouldbeshort,sothatwaterwill
reachthedownstreamendwithoutexcessivepercolationlosses.
•Inclaysoils,theinfiltrationrateismuchlowerthaninsandysoils.Furrowscanbe
muchlongeronclayeythanonsandysoils.
Furrowlayout
Generally,theshape,lengthandspacingaredeterminedbythenaturalcircumstances,
i.e.slope,soiltypeandavailablestreamsize.However,otherfactorsmayinfluence
thedesignofafurrowsystem,suchastheirrigationdepth,farmingpracticeand
thefieldlength.

37. Suitableslopes
Uniformflatorgentleslopesarepreferredforfurrowirrigation.Theseshouldnotexceed
0.5%.Usuallyagentlefurrowslopeisprovidedupto0.05%toassistdrainage
followingirrigationorexcessiverainfallwithhighintensity.
FurrowStreamsize
Thesizeofthefurrowstreamisonefactorwhichcanbevariedafterthefurrowirrigation
systemhasbeeninstalled.Thesizeoffurrowstreamusuallyvariesfrom0.5to2.5
litrespersecond.
Themaximumsizeofirrigationstreamthatcanbeusedatthestartoftheirrigationis
limitedbyconsiderationsoferosioninfurrows,overtoppingoffurrowsand
preventionofrunoffatthedownstreamend.Themaximumnon-erosiveflowratein
furrowsisestimatedbythefollowingempiricalequation:
Inwhich,
q
m=maximumnonerosivestream,lts/sec
s=slopeoffurrowexpressedasapercents
q
m
60.0


38. The average depth of water applied during an irrigation can be calculated from the
following relationship:
In which
d = average depth of water applied, cm
q = stream size, litres per second
t = duration of irrigation (elapsed time), hours
w = furrow spacing, metres
L = Length of furrow, metresL x w
x t360 x q
d

39. Subirrigation
•Insubirrigation,waterisappliedbelowthegroundsurfacebymaintainingan
artificialwatertableatsomedepth,dependinguponthesoiltextureandthedepth
oftheplantroots.Waterreachestheplantrootsthroughcapillaryaction.Watermay
beintroducedthroughopenditchesorundergroundpipelinesortrenchesvaryfrom
30to100centimetersandtheyarespacedabout15to30metresapart.Thewater
applicationsystemconsistsoffieldsupplychannels,ditchesortrenchessuitably
spacedtocoverthefieldadequatelyanddrainageditchesforthedisposalofexcess
water.
•Thesub-irrigationmethodrequiresratherspecialsiteconditionsasitisnecessaryto
havecompletecontrolofthewatertablethroughcontrolledwaterapplicationand
drainage.
•Thesoilprofilemustalsocontainabarrieragainstexcessivelossesthroughdeep
percolation,eitheranearlyimpermeablelayerinthesubstratumoranaturallyhigh
watertableonwhichaperchedorartificialwatertablecanbemaintained
throughoutthegrowingseason.
•Subirrigationcanbeusedforsoilshavingalowwaterholdingcapacityandahigh
infiltrationratewheresurfacemethodscannotbeusedandsprinklerirrigationis
expensive.Sincethemethodrequiresanunusualcombinationofnaturalconditions,
itcanbeusedinonlyafewareas.

40. Sub-irrigation