英文河流动力学水力学Project【文章】

RelevancebetweenStreamBarbLengthandBankErosionAnalysisUsingDelft-3DFlowModelatSawmillCreekAbstractTheSawmillCreekisasmallcreakwhichislocatedinOttawa,Canada.ItgeneratesfromthesouthofLesterRoad,flowingthroughseveralprimaryresidentialareaandfinallydrainsintoRideauRiver.Thereisawiderangeofdischargeandwaterlevelfluctuationtakingplaceinsawmillcreek.AndthewatershedofSawmillCreekrespondsquicklytobigrainfalleventsacrosstheyear.SeveralbendsinSawmillhavewitnessednotablebanderosionandaquatichabitatsreductionintherecentyearsduetohighflowrateanddistinctsecondaryflowwhichistowardstheouterbanknearthewatersurfaceandtowardstheinnerbanknearthebedatthebends.SeveralbarbshavebeenconstructedintwoprimarybendsinOctober,2009andtheresultandfollowingmeasurementshowimprovementsinthebanderosionandaquatichabitatsproblems.Theobjectiveofthispaperistryingtostudytherelevancebetweenthelengthofbarbsandbanderosionreductioneffecttofindtheproperdesignplanforstreambarbsandobtainthebesteffectofbanderosionreductionandaquatichabitatsprotection.Thethreedimensionalhydraulicsoftware,Delft-3D,isappliedtostudythebarbseffectinthispaper.1.INTRODUCTION1.1.IntroductiontoSawmillCreekAsItisshowninFigure1.SawmillCreekbeginsinawetlandsouthofLesterRoad,Ottawa,flowstowardswestandthentowardsnorththroughSouthKeysandFigure1.TheLocationandFlowPathofSawmillCreek(SawmillCreek2014SummaryReport,2014)HeronParkandfinallyflowsintotheRideauRiverneartheintersectionofBankStreetandRiversideDrive.ThetotalwatershedofSawmillCreekis27.73km2andthetotallengthisapproximately11km.Thesurficialgeologyconditionhasahighdegreeofdiversification,consistingof40%sand,29%clay12%gravel,9%diamicton,6%organicdepositsand4%Paleozoicbedrock.Thesurficialgeologyinthewatershedareaismainlymarineclayplainswithsandandrockridges(RVCA,2008).Thenaturalwatercourseaccountsfor41%ofthetotalwatercourseandtherestsectionischannelized.AccordingtoSawmillCreek2014SummaryReport,therewere26aquaticspecies,including4gamefishspecies,observedin2014andItisshowninTable1.Table1.FishSpeciesObservedinSawmillCreekin2004(SawmillCreek2014SummaryReport,2014)Figure2.TheFluctuationofDischargeandWaterSurfaceElevation(WSE)inOneYearfor2009(E.C.Jamiesonetal.,2013)AlthoughSawmillCreekisoneofthelastfree-flowingcoolwaterstreamsleftintheurbancoreoftheCityofOttawa,thelowerandmiddlesreachesofthecreekarehighlyurbanizedandthecreekcorridorisdegradedandconfinedbydevelopmentandtransportationinfrastructure(RVCA2012).ThelanduseinSawmillCreekwatershedincludes48%urban/rural,16%woodedarea,12%transportationarea,11%wetland,1%agriculture,1%waterbodyand11%unclassifiedarea.54%ofthelandusewasmadeupofresidential,industrialorcommercial,infrastructureandrecreation.ThehighdegreeoftheurbanizationandquickrespondtorainfallinheavyrainfalleventsdirectlycauseswiderangeofwaterlevelfluctuationinSawmillCreekwatershed.Figure2showsthedischargeandwatersurfaceelevationfluctuationconditionacrossoneyearinSawmillCreek.1.2BankErosioninSawmillCreekBankErosionisakindofflow-bankinteractionchangeprocessduetostronglysecondaryflowwhenwaterflowsinthebend.Asflowapproachesthebend,theflowrateneartheouterbandisfasterthanthatneartheinnerbank,whichcausesthelowcohesivematerialatthesurfaceoftheouterbankerodedandgradualsedimentationattheinnerbank.Figure3.ErosionalongSawmillCreek(SawmillCreek2014SummaryReport,2014)Excessiveerosionanddepositionofsedimentwithinastreamhaveadetrimentaleffectonthebankstability,channelchangeandaquatichabitat.Andpoorbankstabilitycausedbybankerosioncanmakethebankbecomeeasiertobeeroded.WithincreaseinrunoffduringrainseasoninOttawawilladjusttoaccommodatetheadditionalflow,increasingstreambankerosion.Acceleratedstreambankerosionispartoftheprocessasthestreamseekstoreestablishastablesizeandpattern.Damagingorremovingstreamsidevegetationtothepointwhereitnolongerprovidesforbankstabilitycancauseadramaticincreaseinbankerosion(SteamNotes,Volume1Number2).Thelossofbankvegetationisalsoasignificantproblemduetotheinteractionbetweenbankfailureandbankerosion,resultingintreesfallingintothestreamandthepotentialtoimpactinaquatichabitatandmigrationpath.Figure3showshighlevelsofbankerosionwereobservedalongmanysectionsofSawmillCreekdownstreamofWalkleyRoad.Figure4showstheimageofbankerosionhappeninginonebendofSawmillCreek.Figure4.ErosioninOneBendofSawmillCreek(SawmillCreek2014SummaryReport,2014)1.3.StreamBarbsStreambarbatypeofgroynewhichhasbeenusedforcenturiesunderavarietyofpurposesrangingfromrivertrainingtostreambankprotection.Itisakindoflinearrockstructureconnectedwiththebankandstretchingintothechannel.Itistypicallyanchored.Itisoneofthemostreliableandeconomicallyattractiveapproachesforstabilizingerodingbanksinincisedchannels.ThegeneralconfigurationofbarbsisshowninFigure5.Asforthebendareaofthesmallstream,3or4streambarbsaregenerallyinstalledattheouterbankandparallelwitheachotherwithaspacingrangingfrom1mto3m,determinedbyspecificcondition.Barbsaregenerallyconstructedoutoflargerockriprap,between500and600mmindiameter,withadditionalsmallerriprap(d:50~230mm)alongthebanksideslope(50%above/belowbankfull)upstream