英文河流动力学水力学Project文章.docx
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英文河流动力学水力学Project文章.docx
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英文河流动力学水力学Project文章
RelevancebetweenStreamBarbLengthandBankErosionAnalysisUsingDelft-3DFlowModelatSawmillCreek
Abstract
TheSawmillCreekisasmallcreakwhichislocatedinOttawa,Canada.ItgeneratesfromthesouthofLesterRoad,flowingthroughseveralprimaryresidentialareaandfinallydrainsintoRideauRiver.Thereisawiderangeofdischargeandwaterlevelfluctuationtakingplaceinsawmillcreek.AndthewatershedofSawmillCreekrespondsquicklytobigrainfalleventsacrosstheyear.SeveralbendsinSawmillhavewitnessednotablebanderosionandaquatichabitatsreductionintherecentyearsduetohighflowrateanddistinctsecondaryflowwhichistowardstheouterbanknearthewatersurfaceandtowardstheinnerbanknearthebedatthebends.SeveralbarbshavebeenconstructedintwoprimarybendsinOctober,2009andtheresultandfollowingmeasurementshowimprovementsinthebanderosionandaquatichabitatsproblems.Theobjectiveofthispaperistryingtostudytherelevancebetweenthelengthofbarbsandbanderosionreductioneffecttofindtheproperdesignplanforstreambarbsandobtainthebesteffectofbanderosionreductionandaquatichabitatsprotection.Thethreedimensionalhydraulicsoftware,Delft-3D,isappliedtostudythebarbseffectinthispaper.
1.INTRODUCTION
1.1.IntroductiontoSawmillCreek
AsItisshowninFigure1.SawmillCreekbeginsinawetlandsouthofLesterRoad,Ottawa,flowstowardswestandthentowardsnorththroughSouthKeysand
Figure1.TheLocationandFlowPathofSawmillCreek
(SawmillCreek2014SummaryReport,2014)
HeronParkandfinallyflowsintotheRideauRiverneartheintersectionofBankStreetandRiversideDrive.ThetotalwatershedofSawmillCreekis27.73km2andthe
totallengthisapproximately11km.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.
1.2BankErosioninSawmillCreek
BankErosionisakindofflow-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.StreamBarbs
Streambarbatypeofgroynewhichhasbeenusedforcenturiesunderavarietyofpurposesrangingfromrivertrainingtostreambankprotection.Itisakindoflinearrockstructureconnectedwiththebankandstretchingintothechannel.Itistypicallyanchored.Itisoneofthemostreliableandeconomicallyattractiveapproachesforstabilizingerodingbanksinincisedchannels.ThegeneralconfigurationofbarbsisshowninFigure5.
Asforthebendareaofthesmallstream,3or4streambarbsaregenerallyinstalledattheouterbankandparallelwitheachotherwithaspacingrangingfrom1mto3m,determinedbyspecificcondition.Barbsaregenerallyconstructedoutoflargerockriprap,between500and600mmindiameter,withadditionalsmallerriprap
(d:
50~230mm)alongthebanksideslope(50%above/belowbankfull)upstreamofeachbarbtoprovideadditionalprotectioninthearea.(E.C.Jamiesonetal.,2009)Spurswerespacedatroughlytwicetheaveragebaseflowchannelwidth(<7m)withlengthsroughly40percentoftheaveragewidth.Crestswerelevel,2mwide,and1mabovethebed,orabout60cmabovebaseflowwatersurfaceelevation.Stonesizerangedfrom0.2to450kg,with50to85percentofthestonesweighinglessthan36kg(FD.Shieldsetal.,1998).
Figure5.ConceptualDrawingofSpurs(darkerrock)
(FD.Shieldsetal.,1998)
Thisconfigurationredirectstheattackingcurrentandtheprimarysecondaryflowcellawayfromtheouterbanktowardsthecentreofthechannel(Minoretal.,2007,Jamiesonetal.accepted).Moreover,unlikeotherbankprotectionmeasures(e.g.riprap,concretepavingandgabionwalls),streambarbsrequirelessmaterialandcanpromotevegetatedstreambanks,maintaindeeppoolhabitatthroughthedevelopmentofscourholesatbarbtipsandincreaseaquaticspeciesdiversity(Shieldsetal.,1998;Engelhardetal.,2004).
However,Streambarbsdonotaddressbankfailureduetosoilinstabilityand
Drawdown(TechnicalNote23:
DesignofStreamBarbs,U.S,2005).Therefore,additionalworkshouldbedonebeforethebarbsinstallationsuchasstreamcleanup,vegetativeplantingandsitemonitoring.Theplanistoincorporatevegetativeplantingandotherbioengineeringpracticesduringtheconstructionphasetoaddresstheseadditionalmechanismsofbankfailure(E.C.Jamiesonetal.,2009).Moreover,vegetationprovidesadditionalroughnesstodissipateenergyalongthestreambankandenhanceswildlifehabitatandwaterquality(E.C.Jamiesonetal.,2009).
1.4TargetReachInformation
Thetargetreachofthisstudyisa50-mreachinSawmillCreek,whichgenerallyconsistsoftwosmallbendsandreceivesapproximately90%ofthecontributingwatershedarea.Thereachisexperiencingbankerosionandmasswastingattwoconsecutivebends.Thelineardistanceandareaoferodingbankinthefirst(second)bendwere13.4mand41.7m2(28.0mand46.0m2)(E.C.Jamiesonetal.,2013).Anumberoflargebouldersdominatedthemorphologyofthesecond(downstream)bend,andarifflehadformedclosetotheapexofthebend.(E.C.Jamiesonetal.,2013)targetreachwasselectednotonlybecausetheerodingbanksindicatedthepresenceoferosionprocessesbutalsobecauseofrelativeeaseofsiteaccessandlackofproximitytocriticalinfrastructure.(E.C.Jamiesonetal.,2013)Thesiteimageofthetargetreachandtwobendsarepresentedinfigure2.
Figure6.(A)AerialphotooftheSawmillCreekstudyarea;reddashedline
indicatesrightbankandflowisfromsouthtonorth.(B)Bend1looking
upstream,and(C)outsidebankofbend2lookingdownstream.
(E.C.Jamiesonetal.,2009)
InSeptember2009,aseriesofsevenstreambarbswereinstalledtoprotectthe
twoerodingouterchannelbanksandtoserveasademonstrationprojectfortheuseofthesestructuresinasemi-alluvialchannel(E.C.Jamiesonetal.,2009).Threebarbswereplacedinthefirstupstream)bend,andfourbarbswereplacedintheproceeding(downstream)bend(labeledB4–B7)(Figures1and2)(E.C.Jamiesonetal.,2009).
Figure7.StreambarbsatSawmillCreek:
(a)bend1and(b)bend2.Barbsarenumberedinthedownstreamdirection.Photostakenon9November2009,duringlowflowconditions(discharge,Q~0.3m3/s).(E.C.Jamiesonetal.,2013)
2.OBJECTIVE
Table2.BarbInstallationPlanIntheTwoBendsofSawmillCreek
(E.C.Jamiesonetal.,2009)
Accordingtothebarbdesignplaninpreviousstudy(E.C.Jamiesonetal.,2009),thebarbinstallationanglewasdeterminedduetolaboratoryexperiments(Matsuura,Tetal.,2004andnumericalmodeling(Minor,B.etal,.pp1087-1095).Intheseexperiments,whichconsidered90and135ºchannelbends,optimumba
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