Unit 12 River training work.pdf

River training work

1. Irrigation Engineering
Prepared by
Sh. Rajpal Singh Shekhawat
Lecturer
Department of Civil Engineering
PusaInstitute of Technology
CE -633

2. River training works

3. River
•Ariverisanaturalflowingwatercourse,usuallyfreshwater,
flowingtowardsanocean,sea,lakeoranotherriver.
•Riverstakeofffrommountains,flowfromthemountainousplain
terrains,andfinallyjointheoceans.
•Theriversnotonlycarryhugeamountofwaterbutalsocarrya
tremendousamountofsiltandsedimentwhichiswasheddown
fromthecatchmentareaorgetserodedfromtheirbedsandbanks.

4. River System

5. River Dam
Krishna Nagarjunasagar
Narmada Sardarsarovar
Mahanadi Hirakud
Sutlej BhakraNangal
Bhagirathi Tehri
Koyna Koyna
Chambal Gandhi sagar
Periyar Periyar
Tunghabadra Tunghabadra
Krishna Srisailam
Kaveri Mettur
Rihand Rihand
Narmada Indira Sagar
Ukai Ukai

6. Types of River
•ClassificationofRiversontheBasisoftheTopographyofthe
RiverBasin.
1.Riversinhills(Upperreaches);
2.Riversinalluvialplains,knownasriversinfloodplains
(Lowerreaches);
3.Tidalrivers
Riversinhills(upperreach):
•Theriversgenerallytakeofffromthemountainsandflowthrough
thehillyregionsbeforetraversingtheplains.Theseupperreachesof
theriversmaybetermedasriversinHills.
•Inthistype,theflowchannelisgenerallyformedbytheprocessof
degradation(erosion).Thesedimenttransportedinthisreachisoften
differentfromtheriverbedmaterial,sincemostofitcomesfromthe
catchmentduetosoilerosion.

7. Types of River
•Theseriver-reachesarehighlysteepwithswiftflow,andforming
rapidsalongtheircourses.Thebedsandbanksofsuchriversareless
susceptibletoerosion.

8. Types of River
RiversinAlluvialFloodPlains(LowerReaches):
•Thechiefcharacteristicsoftheseriverreachesisthezig-'zagfashion
inwhichtheyflow,calledmeandering.
•Theymeanderfreelyfromonebanktoanotherandcarrysediment
whichissimilartobedmaterial.
•Materialgetserodedconstantlyfromtheconcavebank(outeredge)
ofthebendandgetsdepositedeitherontheconvexside(inner·
edge)ofthesuccessivebendsorbetweentwosuccessivebendsto
formabar.
•Riversinfloodplainscanbefurtherclassifiedas:
a) Aggrading Riverd) BraidedRiver
b) Degrading Rivere) Deltaic River
c) Stable River

9. Types of River

10. Types of River
•AggradingRiver:Iftheriveriscollectingsedimentandisbuilding
upitsbed,itiscalledanaggradingorofanaccretingriver.An
aggradingriverisasiltingriver.suchariverincreasesitsbedslope,
whichiscalledbuildingupofslope.Thesiltingmaybedueto
variousreasons,suchasheavysedimentload;constructionofan
obstructionacrosstheriver,suchasadamoraweir.Thistypeof
river,usually,hasstraightandwidereacheswithshoalsinthe
middle,whichshiftwithfloods,dividingtheflowintoanumberof
braidedchannels.
•DegradingRiver:Iftheriverbedisconstantlygettingscoured
(eroded)toreduceanddissipateavailableexcesslandslope,then
theriverisknownasadegradingriver.Itmaybefoundeither
aboveacut-offorbelowadamoraweirorabarrage,etc.

11. Types of River
•StableRiver:Ariverwhichdoesnotchange-itsalignment,slope
anditsregimesignificantly,iscalledastableriver.Thebehaviour
ofaparticularreach(whethertobeaggrading,degradingorstable)
dependsmainlyuponthevariationsofsiltcharge(sizeaswellas
quantity)andflowdischargewithtime.
•BraidedRiver:Whenariverflowintwoormorechannelsaround
alluvialislands,itisknownasabraidedriver.Thebraidedpattern
inariverdevelopsafterlocaldepositionofcoarsermaterial,which
cannotbetransportedunderprevailingconditions'offlow.

12. Types of River
•DeltaicRiver:Ariverbeforeitjoins
thesea,getsdividedintobranches,
thusforminga∆shaped,called
deltaicriver.Astheriverapproaches
thesea,itsvelocityisreduced,and
consequentlythechannelgetssilted
andwaterlevelrisesresultingin
formationsofnewchannels.

13. •TidalRiver:Thetailreachesoftheriversadjoiningtheoceansare
affectedbythetidesintheocean.Theoceanwaterenterstheriver
duringthefloodtideandgoesoutintotheoceanduringtheebb
tide.Theriver,therefore,undergoesperiodicalriseandfallinits
waterlevel,dependinguponthenatureofthetide.Thedistanceup
towhichthetidaleffectisexperienced,dependsuponvarious
factors,suchastheshapeandconfigurationoftheriver,thetidal
range,freshetdischarge,etc.
Types of River

14. Behaviourof River
Themainfactorwhichisresponsiblefordifferentbehaviourofrivers
isthesiltandsedimentthatflowsintheriver.Thesedimentcarriedby
theriverposesnumerousproblems,suchas:increasingofflood
levels,siltingofreservoirs,siltingofirrigationandnavigation
channels;meanderingofrivers,splittingupofariverintoanumberof
interlacedchannels,etc.Themeanderingcausestheriverstoleave
theiroriginalcourses,forcesthemtoflowalongnewcourses.
➢StraightReaches:Inastraightreachofariver,therivercross-
sectionisintheshapeofatrough,withhighvelocityflowinthe
middleofthesection.Sincethevelocityishigherinthemiddle,the
watersurfacelevelwillbelowerinthemiddleandhigheratthe
edges.Duetotheexistenceofthistransversegradientfromsides
towardsthecentre,transverserotarycurrentsgetdeveloped.
However,straightreachesareveryfewinalluvialrivers.

15. oBends:Everyalluvialrivertendstodevelopbends,whichare
characterisedbyscouringontheconcavesideandsiltingonthe
convexside.Thesiltingandscouringinabendmaycontinuedueto
theactionofthecentrifugalforce.
Behaviourof River

16. oMeanders:Formationofsuccessivebendsofreverseordermaylead
totheformationofacompleteScurvecalledmeander.When
consecutivecurvesofreverseorderconnectedwithshortstraight
reachescalled(crossings)aredevelopedinariverreach,theriveris
statedtobeameanderingriver.
oWhenonceariverdeviatesfromitsaxialpathandacurvatureis
developed(eitherduetoitsowncharacteristicsorduetothe
impressedexternalforces),theprocessmovesdownstreamby
Behaviourof River
buildingupshoalsonthe
convexsidebymeansof
secondarycurrents.
Theformationofshoalson
theconvexside,resultsin
furthershiftingoftheouter
bankbyerosiononthe
concaveside.

17. Behaviourof River
oMeanderingisbasedupontheextraturbulencegeneratedbythe
excessofriversedimentduringfloods.
oTherearefourvariables,whichgovernthemeanderingprocess.
Theyare:(i)Valleyslope,(ii)Siltgradeandsiltcharge,(iii)
Discharge,(iv)Bedandsidematerialsandtheirsusceptibilityto
erosion.

18. •Cutoff:Inanexcessivelymeandering
river,aparticularbendmay
sometimesbeabandonedbythe
formationofastraighterandashorter
channel.Theprocess,whereby,this
chordchannelisdevelopedorthe
chordchannelitself,istermedascut-
off.
•Itisevidentthatameander
increasestheriverlengthbutacut-
offreducestheriverlength.
Behaviourof River

20. Developmentofcutoff:
•Ameanderingriverflowingalongthecurvedpathhasashallow
sidechannelbesidesitsmaincurvilinearpath.Thismaybecreated
byfloodsspillingovertheriverbank.Thewaterflowmoreand
moretowardthesidechannel.
•Whenflowstartsreducinginthemaincanal,moreandmoresilting
occurinthemainchannel,whichfurtherincreasestheflowinthe
sidechannel.
•Theprocesscontinuesandfinallyatimemaycomewhentheentire
waterstartsflowingfromthefulldevelopedchordchannelandthe
curvilinearpathgetssiltedup.
•Theperiod,overwhichtheopeningofachordchannelmaturesinto
afull-fledgedcut-offmayvaryconsiderably,dependinguponthe
localconditions.Itmaytakesixmonths,ayear,orevenfiveorten
years.
Behaviourof River

21. River Training works

22. River Training works
oRivertrainingcoversallthoseengineeringworkswhichare
constructedonariver,soastoguideandconfinetheflowtothe
riverchannel,andtocontrolandregulatetheriverbed
configuration,thusensuringsafeandeffectivedisposaloffloods
andsedimentloads.
Objectivesofrivertrainingworks:
oTopreventtheriverfromchangingitscourseandtoavoid
outflankingofstructureslikebridges,weirs,aqueducts,etc.
oTopreventfloodingofthesurroundingcountriesbyprovidinga
safepassageforthefloodwaterswithoutovertoppingthebanks.
oToprotecttheriverbanksbydeflectingtheriverawayfromthe
attackedbanks,.
oToensureeffectivedisposalofsedimentload.
oToprovideminimumwaterdepthrequiredfornavigation.
oTheaimofrivertrainingistoachieveultimatestabilityoftheriver.

23. Methods of River Training
oThefollowingarethegenerallyadoptedmethodsfortrainingrivers,
includingbankprotection:
(1)MarginalembankmentsorLevees._
(2)Guidebanks.
(3)GroynesorSpurs.
(4)Artificialcut-offs.
(5)Pitchedislands.

24. Embankments or levees
Embankment:
oThefloodsmaybepreventedfromsubmergingthecountryby
constructingearthembankments.Theyaregenerallyconstructedup
toaheightof12m.Theyaredesignedandconstructedinthesame
wayasanearthdam.Theembankmentsaregenerallyconstructed
paralleltotheriverchannel.
oDependinguponthepositionoftheembankmentsitisclassifiedinto
twotypes:i)MarginalEmbankmentsordykesorlevees
ii)RetiredEmbankments
MarginalEmbankments:
oMarginalembankmentsaregenerallyearthenembankments,running
paralleltotheriver,atsomesuitabledistancefromtheriver.
oTheymaybeconstructedonbothsidesoftheriveroronlyoneside,
forsomesuitableriverlength,wheretheriverispassingthrough
townsorcitiesoranyotherplacesofimportance.

26. •Theseembankment-walls,retainthefloodwaterandthus,
preventingitfromspreadingintothenearbylandsandtowns.A
leveeoradykeismainlyusedforfloodprotectionbycontrolling
theriver.Thealignmentofleveesshouldfollowthenormal
meanderingpatternoftheriver.
•Theyaredesignedtoholdupthewateruptoamaximum
anticipatedHFLwithoutthepossibilityofovertoppingandwitha
viewtowithstandallexternalpressures.Thisconditionismetwith
byprovidingsufficientfreeboard,bedwidth,topwidthandstone
protectiononadequateslopes.
•Thetopwidthoftheembankmentvariesfrom2.5to10m.Thetop
leveloftheleveeshouldbedecidedbyleavingasufficient
freeboardvaryingbetween0.3to1.5mabovethehighfloodlevel.
•Thesideslopeontheriversidevaryingbetween2:1to5:1,land
sideslopesbetween2:1to7:1.
•Onthesideoftheriver,stonepitchingisprovidedforprotectingthe
bankfromtheeffectsofwave.

27. •Marginalembankmentshelpintoincreasetherateoftravelofwater
byconfiningtheriverwithinnarrowlimits.Thus,Thesiltdeposition
willbelessinadikedrivercomparedtothatinanun-dikedriver.
•Inadikedriver,thesiltwillbedepositedonlyintheconfinedfixed
area(i.e.areaenclosedbetweendikesandriver),andtherefore,the
bedleveloftheriveraswellasthatofthisenclosedareawill
increase.
•Theyhelpintoreclaimthelandforcultivationpurpose.

28. RetiredEmbankments:
•Theembankmentsconstructedatdistancefromtheriverarecalled
retiredembankments.
•Thusretiredembankmentsaretheintermediatetypebetweenthe
caseofmarginalembankmentsandriverwithnoembankments.
Retiredembankmentsaregenerallyconstructedonalowerground
awayfromthebanks.
Theadvantagesoftheretiringembankmentsare:
•Theycauselesserinterferencewiththenaturaloperationofsilt
depositedbytheriveroverthecountryandraisingitslevel.
•Theyenabletheriverfloodtobespreadovermorearea,thus
creatinganartificialstorageduetothedetentionofwaterforsome
period.
•Byprovidingawiderwaterwaytheyenablethehighfloodwater
leveltobelowerthanwouldbethecasewithcloserbanks.
•Thebanksbeingawayfromtheriverarenotsofrequentlyattacked
aswouldbethebanksneartheriveredge.
•Enoughopportunityisgiventotheseembankmentsforsettlement
andconsolidation.

29. Guide banks

30. Guide banks

31. Guide banks
•Ifanengineeringstructure,suchas,aweirorabarrageorabridge,
etc.isconstructedacrossariver,theriverwidthisreducedand
trainedinsuchafashion,astoensurenotonlyasafeandexpeditious
disposaloffloodwaterbutalsotoensureapermanentreasonable
widthofthewaterwayfortheriverflow.
•Weknowthatthealluvialriversshifttheircoursesduetovarious
reasons.Now,iftodayastructuresuchasabridge,isconstructed
acrosstheexistingriverwidth,theotherday'therivershiftthe
course,theconstructionofstructurebecomeuseless.
•Hence,astructuresuchasaweir,orabarrage,orabridge,etc.is
extendedinasmallerwidthoftheriver,andriverwateristrainedto
flowalmostaxiallythroughthistroughwithoutout-flankingthe
structure.Theriverisnormallytrainedforthispurposewiththehelp
ofapairofguidebanks.

32. Guide banks
•Thebanksconstructedforconfiningandguidingtheflowofthe
riverinareasonablewaterwayarecalledguidebanks.
•Themainobjectsofguidebanksare:
1)Tocreateareasonablewaterwayforconstructingabridgeora
weirorabarrage.
2)Topreventobliqueapproachtotheheadregulator.
3)Topreventout-flankingofstructures.
4)Toprotecttheregulatorfromtheriverattack.
5)Toincreasethemaximumdischargeatallpointd/softheweir.
•Theguidebanksaregenerallyprovidedinpairs,symmetricalinplan
andmayeitherbekeptparallelormaydivergeslightlyup-streamof
theworks.Symmetricalandparallelguidebanksareusually
adopted.

33. •Beforethewaterentersintothetroughformedbetweenthesetwo
guidebanks,theflowmayhavetobepartiallycontrolledand
directedwiththehelpofmarginalbundsorbygroynesorboth.
•Theguidebanks,usually,consistoftwoheavilybuiltembankments
intheriverintheshapeofabellmouth.
•Theportionoftheriverbetweenthenormalriverbanksandtheguide
banksisclosedbyordinaryembankmentscalledapproach
embankments.
•Thesiteforengineeringstructureshouldbewherethedistance
betweenthebanksisminimum.Bridgesshouldtherefore,preferably
bebuiltinthetransitionreaches,ratherthanonthebends.
•ThetoplevelofguidebanksisgovernedbyHFL,afflux,velocity
head,andfreeboard.Itcanbeobtainedbyaddingallthesefour
values.
•Byafflux,wemeantheriseinthehighfloodleveloftheriver,
upstreamoftheweir,orbarrage,asaresultofitsconstruction.

34. •Theguidebanksaregenerallyprovidedinpairs,symmetricalinplan
andmayeitherbekeptparallelormaydivergeslightlyupstreamof
theworks.Symmetricalandparallelguidebanksare,hence,usually
adopted,unlessthelocalconditionswarrantotherwise.
•AccordingtoSpring,thelengthoftheupstreampartoftheguide
bankshouldbeequalto1.1Landthelengthoftheguidebankonthe
downstreamsideshouldbebetween0.1Lto0.2L.
•AccordingtoGales,theupstreamlengthoftheguidebankisI.25L
forflooddischargesupto20,000cumecs,and1.5Lforflood
dischargesmorethan20,000cumecs.Thelengthoftheguidebank
onthedownstreamsideshouldbetakenequalto0.25L.
•Theendsofthesebanksarecurvedinordertoallowsmoothentryof
waterandalsotoprotectthebank.Theupstreamcurvedportionofa
guidebankiscalled'theimpregnablehead'.Asafevalueforthe
radius(R)maybetakenequaltoR=0.45L.Theupstreamcurveis
extendedtosubtendanangleof120°to140°atitscentre.

36. •Thedownstreamportionoftheguidebankensuresthesafetyof
approachembankmentsandpreventstheriverfromattackingthem.
ThispurposecanbeWellservedbyproviding-shortguidebundwith
sharpcurvedhead.Aradiusequaltohalftheradiusattheupstream
side,maybeadoptedhereandsweepangleof45°to60°.
•Thestraightportionoftheguidebankiscalledtheshankportion.The
guidebanksshouldhaveaminimumtopwidthof4metressoasto
providesufficientcarriage-way.Sideslopesmayvaryfroml.5H:1
Vto2.5H:1V,(butgenerallykeptas2H:1V),dependingonthe
constructionmaterialsandtheheightofthebund.Afreeboardof1.2
to1.5misgenerallyprovided.
•Theslopingwatersideoftheentireguidebundaswellasthesloping
rearsideofthecurvedportionsarepitchedwithonemanstoneor
concreteblocks.

37. Spurs or Groynes

38. oGroynesaretheembankmenttypestructures,constructedtransverse
totheriverflow,extendingfromthebankintotheriver.Theyalso
calledtransversedykes.
oTheyareconstructed,inordertoprotectthebankfromwhichthey
areextended,bydeflectingthecurrentawayfromthebank.
oAsthewaterisunabletotakeasharpembayment,thebankgets
protectedforcertaindistanceupstreamanddownstreamofthe
groyne.
oHowever,thenoseofthegroyneissubjectedtotremendousactionof
water,andhastobeheavilyprotectedbypitching.Theactionof
eddiesreducesfromtheheadtowardsthebank,and,therefore,the
thicknessofslopepitchingandaproncanbereducedaccordingly.
oThegroynesmaybebuilteitherperpendiculartothebanklineor
theymaybeinclinedupstreamordownstream.
Spur or gryones

39. •Agroynealignedperpendiculartothebanklineisknownasan
ordinarygroyneoranormalgroyne.
•Agroynepointingupstreamhasthepropertyofrepellingtheflow
awayfromthebank,andiscalledrepellinggroynes.
•Ontheotherhand,agroynepointingdownstreamhasthepropertyof
attractingtheflowtowardit,andiscalledanattractinggroyne.
•Thegroynesare,therefore,generallyalignedeitherperpendicularto
thebankorpointingupstream.The'perpendicularalignment'is
generallyusedonconvexbanks,andthe'upstreampointing
alignment'isgenerallyusedonconcavebanks.
•Thelengthsofthegroynesdependuponthepositionoftheexisting
banklineandthedesignedorexpectedbanklinefortrainedriver.
Toolonggroynesoneasilyerodiblerivers,aresusceptibletodamage
andfailure.

40. •Aseachgroynecanprotectacertainlength,theprimaryfactor
governingthespacingbetweentwoadjacentgroynes,istheir
length.Apartfromthelength,thespacingmaybegovernedbythe
followingfactors:
(a)Typeofbankwherethegroyneistobelocated.Largerspacingis
requiredforlocatinggroynesonconvexbanks,andasmallerone
forconcavebankswithintermediatevaluesatthecrossings.A
spacingof2to2.5timesthelengthofthegroyneisgenerally
adoptedatconvexbanks,whileaspacingequaltothelengthof
thegroyneismostlyadoptedforconcavebanks.
(b)Thewidthoftheriver.Forriversofequalflooddischarges,a
largerspacingispreferredforwiderriversthanfornarrower
rivers.
(c)Typeofgroyne.Ahighervalueofspacingmaybeusedfor
permeablegroynesascomparedtothatrequiredforimpermeable
groynes.

41. •Thelengthofspurwhichprojectsintotheriveriskeptatabout15
to20morso,andthespacingbetweenthespursiskeptatabout50
morso.Thelengthandspacingareinterdependentoneachother.
•Impermeablegroynesarealsocalledassolidgroynesor
embankmentgroynes.Thesegroynesmayberockfillembankments
orearthernembankments,armouredwithstonepitching,concrete
blocks,etc.Thesegroynesarecalled'impermeablegroynes'
becausetheydonotallowanysignificantflowthroughthem.
•Permeablegroynespermitrestrictedflowthroughthem.Permeable
groynes,simplyobstructtheflow,reducingitsvelocityandcausing
siltdeposition.Theyare,therefore,bestsuitedforriverscarrying
hugesedimentloadinsuspension.Thesiltparticlespresentinthe
flowgetdepositedinthespacethroughwhichwaterflows.
Therefore,theybecomeimpermeableincourseoftime,depending
onthesiltchargecarriedbytheriverwater.Theyhelpinreducing
corrosivestrengthoftheriver.

42. •A'pitchedisland'isanartificiallyconstructedislandintheriverbed
andisprotectedbystonepitchingonallsides.
•Becauseoftheturbulencegeneratedbytheislandinitsvicinity,the
riverchannelaroundtheislandgetsdeepenedandthus,attractingthe
rivertowardsitselfandholdingitpermanently.
Pitched island
•Pitchedislandsmaytherefore,helpinattractingthecurrenttowards
themselvesandthus,reduceundueconcentrationontheopposite
banks.Thedeviceofpitchedislandasarivertrainingmeasureisofa
recentoriginandisstillintheexperimentalstages.
•pitchedislandisaveryeffectivemeansofcontrollingandtraining
rivers,especiallyinthevicinityofcontrolpoints,suchasabridgeora
weirorabarrage,etc.

43. •Whenameandergoesonincreasingandmayendangersome
valuablelandorproperty,thentherivercoursemaybestraightened
byinducinganartificialcut-off.
•Forinducinganartificialcut-off,onlyapilotchannelisrequiredto
beexcavatedincaseofrivershavingeasilyerodiblebeds.
•Thefloodwaterwillgraduallyenlargethepilotcuttotherequired
cross-sectionandwillabandontheoldcurvedchannel,provided,the
circumstancesforthedevelopmentofthiscut-offarefavourable.
•Thecompleteformationofacut-offisgenerallybroughtabout
slowlyandslowly.Thecommonpracticeistomakepilotcutswhich
carry8to100percentofdischargeinthebeginning,andare
developedsubsequentlytocarryabout40to50percentofthetotal
riverdischarge.
•Sinceacut-offhelpsinreducingfloodheightsandfloodperiods,it
helpsinshorteningthenavigationcourseandalsohelpsin
protectingendangeredestablishments.
Artificial cutoff

44. Thank you