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RiverandChannelTrainingWorks
Rivertrainingworksareconstructedfor
avarietyof reasons,butthefundamental
objectiveis to restricthorizontalmove-
mentoftheriverchannel.Trainingworks
canalsobeusedto improvenavigation
byrestrictingthewidthof thechannel.
Trainingworksareinstalledwherelocal
infrastructureor agriculturall.andneeds
tobeprotectedfromthedamagewhich
wouldresultfromerosionof theriver
banks.Trainingworksarealsoprovided
atbridgesandotherstructurestoimproveflowconditionsandpreventoutflanking.
Rivertrainingcanbeachievedbyriverbankprotection(revetment),groynes(spurs),oracombinationof thetwo.
Gabionsareidealforbothapplicationssincetheyhavetheconsiderableadvantagesof flexibilityandpermeability.
RiverBankProtection
Riverbankprotectionisachievedbyplacingarevetment
whichpreventserosionof thebank.In generalthebank
protectionisalignedroughlyparalleltotheflowsoasto
minimisethehydraulicloadingandtoavoidadverseef-
fectsontheriverregime.
Thedesignofanyrivertrainingworksshouldbecarried
outwithafullunderstandingofthefluvialprocesses
involved.Thethreemainaspectstobeconsideredare:
. thevelocityoftheflow;
. thelikelymaximumdepthofscourintheriverchannel;
. theoverallextentandgeometryoftheworks.
FlowVelocity- Designflowvelocitiesmaybeobtainedfrommeasurementsonsiteor fromhydraulicmodelsofthe
river(eitherphysicalornumerical).Intheabsenceofsuchdata,theManningequationcanbeusedtoestimateaverage
velocityinthechannel:
where
Manning'sEquation1
V=- R 2/3S II2n
R =hydraulicradius=cross-sectionalareawettedperimeter
S=longitudinalchannelslopen =Manning'sroughnesscoefficient
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Scour-Failureof arevetmentis oftentheresultof inadequateprotectionagainstscouratthetoeof therevetment.
Rigidrevetmentshavetheconsiderabledisadvantagethattheyareeasilyundenninedbyscour.Gabionsontheother
handcandefonninacontrolledmannerattheonsetof scourandmaintaintheprotectionof thechanneledge.
Gabionmattressscourapronslaidatthetoeof theriverbankshouldextendintotherivetbetween1.5and2.0times
theanticipatedmaximumscourdepth.Thisensuresthatthegabionmattresstakesupthescouredprofileandcontin-
uestoprotectthebankagainsterosion.
Estimatinglikelydepthof scouris difficulttodowithanyaccuracy,andthereis nosubstitutefor localknowledge
or fieldmeasurements.However,it shouldbenotedthatlargescourholesfonnedin floodscanbe filledin by
sedimentdepositionduringthefloodrecession,soaccuratephysicaldataarehardtocomeby.Thedesignershould
ensurethatfonnulaeusedforscourdepthestimatesareappropriateforthebedmaterialconsidered.
Groynes
Groynes(orspurs)deflectorguideflowawayfromthevulnerableriverbanks.Theycanthereforebeusedbothfor
bankprotectionandtohelpmaintainanavigablechannel.
Groynescannotbespacedtoofarapartotherwisetheriverwill attackthebankinbetween.Furthennore,groynesby
theirnatureobstructtheflowandwill generateturbulenceandconsequentialscour.Groynesthereforerequirecareful
detailingtoensurethattheyarenotoutflankedorundenninedin floods.
Groynedesign
Mal) lobepro~ecllSd
Chenneledgeprolecllon u/.of IIrsl groyne
Flow direclion
Croyne slepped lo reducelurbulence. and lIow ob.lrucllon
SECI'(ON
f-I~"I
, 1..1-------IIIIII1-------.-L T-
I
l-'~It
S =3 to 4 X L
where
0.03y1.33y ~L ~O.25BS< 2n
y =meandepthof flow atthedesigndischarge(m)n=Manning'sroughnesscoefficient.
FlowdlreclionPLAN
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