外文翻译CCHE1D渠道网络模型的灵敏度分析.docx
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外文翻译CCHE1D渠道网络模型的灵敏度分析.docx
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外文翻译CCHE1D渠道网络模型的灵敏度分析
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外文原文
SensitivityAnalysisoftheCCHE1DChannelNetworkModel
WeimingWu
(1),DalmoA.Vieira
(2),AbdulKhan(3)andSamS.Y.Wang(4)
(1),
(2),(3)and(4),NationalCenterforComputationalHydroscienceandEngineering,SchoolofEngineering,TheUniversityofMississippi,MS38677;PH(662)915-5673/(662)915-7788;FAX(662)915-7796;E-mail:
wuwm@ncche.olemiss.edu
Abstract
TheCCHE1Dmodelwasdesignedtosimulatelong-termflowandsedimenttransportinchannelnetworkstosupporttheDECproject.Ituseseitherthedynamicwaveorthediffusivewavemodeltocomputeunsteadyflowsinchannelnetworkswithcompoundcrosssections,takingintoaccounttheeffectsofin-streamhydraulicstructures,suchasculverts,weirs,dropstructures,andbridgecrossings.Itsimulatesnon-uniformsedimenttransportusinganon-equilibriumapproach,andcalculatesbanktoeerosionandmassfailureduetochannelincision.TheCCHE1Dmodeldecouplestheflowandsedimenttransportcalculationsbutcouplesthecalculationsofnon-uniformsedimenttransport,bedchangesandbedmaterialsortinginordertoenhancethenumericalstabilityofthemodel.Inthispaper,thesensitivityofCCHE1Dtoparameterssuchasthenon-equilibriumadaptationlengthofsedimenttransportandthemixinglayerthicknessisevaluatedincasesofchannelaggradationanddegradationinlaboratoryflumesaswellasinanaturalchannelnetwork.Inthecaseofchanneldegradation,thesimulatedscourprocessisnotsensitivetovariationinvaluesofthenon-equilibriumadaptationlength,butthedeterminationofthemixinglayerthicknessisimportanttothecomputationsoftheequilibriumscourdepthandofthebed-materialsizedistributionatthearmoringlayer.Thesimulatedbedprofilesinthecaseofchannelaggradationandthecalculatedsedimentyieldinthecaseofnaturalchannelnetworkareinsensitivetotheprescriptionofboththenon-equilibriumadaptationlengthandthemixinglayerthickness.TheCCHE1Dmodelcanprovidereliableresultsevenwhenthesetwoparametersaregivenawiderangeofvalues.
Introduction
TheCCHE1Dmodelwasdesignedtosimulatelong-termflowandsedimenttransportinchannelnetworkstosupporttheDemonstrationErosionControl(DEC)project,whichisaninteragencycooperativeeffortamongtheUSArmyCorpsofEngineers(COE),theNaturalResourcesConservationService(NRCS)andtheAgriculturalResearchService(ARS)oftheUSDepartmentofAgriculture.TheCCHE1Dversion2.0wasbasedontheunsteadyflowmodelDWAVNET(DiffusionWAVemodelforchannelNETworks,Langendeon,1996)andthesedimenttransportmodelBEAMS(BedandBankErosionAnalysisModelforStreams,Lietal.,1996).Itwassignificantlyimprovedbyimplementingthedynamicwavemodelandthenon-equilibriumsedimenttransportmodel(Wu,VieiraandWang2000).TheCCHE1DwasintegratedwiththelandscapeanalysistoolTOPAZ(GarbrechtandMartz,1995)andwiththewatershedmodelsAGNPS(Boschetal.,1998)andSWAT(Arnoldetal.,1993),throughanArcViewGIS-basedgraphicaluserinterface(VieiraandWu,2000).TheCCHE1Dhasbeensuccessfullytestedinvariousexperimentalandfieldcases.BecauseseveralparametersinCCHE1Dmustbeprescribedempirically,itisveryimportanttoknowtheresponseofthemodeltotheuncertaintyoftheseparameters.Inthisstudy,thesensitivityofCCHE1Dtomodelparameterssuchasthenon-equilibriumadaptationlengthofsedimenttransportandthemixinglayerthicknessisanalyzedincasesofchannelaggradationanddegradationinlaboratoryflumesaswellasinanaturalchannelnetwork.
DescriptionoftheCCHE1DChannelNetworkModel
HydrodynamicModel.TheCCHE1Dflowmodelsimulatesunsteadyflowinchannelnetworkswithcompoundcross-sectionsusingeitherthediffusivewavemodelorthedynamicwavemodel.ThedynamicwavemodelsolvesthefullSt.Venantequations.ThePreissmannimplicit,four-point,finitedifferenceschemeisusedtodiscretizethegoverningequations.Linearizediterationschemesforthediscretizedgoverningequationsareestablishedandsolvedusingadoublesweepalgorithm.Theinfluenceofhydraulicstructuressuchasculverts,measuringflumes,bridgecrossingsanddropstructureshasbeenconsideredintheCCHE1Dmodel.Stage-dischargerelationsforhydraulicstructuresarederivedsothatthehydraulicstructuresbecomeanintrinsicpartofthenumericalalgorithm.
SedimentTransportModel.TheCCHE1Dmodelcalculatesnon-uniformsedimenttransportinriversusinganon-equilibriumapproach.Thegoverningequationforthenon-equilibriumtransportofnon-uniformtotalloadis
(1)
whereAistheflowarea;Ctkisthedepth-averagedtotal-loadconcentrationofsizeclassk;Qtkistheactualtotal-loadtransportrate;Qt*kisthetotal-loadtransportcapacity;Lsistheadaptationlengthofnon-equilibriumsedimenttransport;andqlkisthesidesedimentdischargefrombanksortributariesperunitchannellength,withthecontributionfrombanksbeingsimulatedbyCCHE1Dbankerosionandbankfailuremodule,andthecontributionfromuplanderosionbeingsimulatedbySWATorAGNPS.
Thesedimenttransportcapacitycanbewrittenasageneralform
(2)
wherepbkisthebedmaterialgradation;Q*tkisthepotentialsedimenttransportrate,whichisdeterminedwithSEDTRAmodule(Garbrechtetal.,1995),Wu,WangandJia’sformula(2000),themodifiedAckersandWhite’s1973formula(ProffittandSutherland,1983),orthemodifiedEngelundandHansen’s1967formula(withWu,WangandJia’scorrectionfactor,2000).
Thebeddeformationduetosizeclasskisdeterminedwith
(3)
wherep′isthebedmaterialporosity,whichiscalculatedwiththemethodsofKomuraandSimmons(1967),Hanetal(1981),orisspecifiedbytheuseraccordingtoavailablemeasurementdata;∂Abk/∂tisthebeddeformationrateofsizeclassk.Thebedmaterialisdividedintoseverallayers.Thevariationofbedmaterialgradationpbkatthemixinglayer(surfacelayer)isdeterminedbythefollowingequation(WuandLi,1992)
(4)
whereAmisthecross-sectionalareaofthemixinglayer;∂Ab/∂tisthetotalbeddeformationrate,definedas∂Ab/∂t=
;Nisthetotalnumberofsizeclasses;p*bkispbkofthemixinglayerwhen∂Am/∂t−∂Ab/∂t≤0,andp*bkisthepercentageofthekthsizeclassofbedmaterialinsubsurfacelayer(undermixinglayer)when∂Am/∂t−∂Ab/∂t>0.
Eq.
(1)isdiscretizedusingthePreissmannimplicitscheme,withitssourcetermbeingdiscretizedbythesameformulationasthatfortheright-handtermofEq.(3)inordertosatisfythesedimentcontinuity.Eq.(4)isdiscretizedbyadifferenceschemethatsatisfiesmassconservation.Acoupledmethodforthecalculationsofsedimenttransport,bedchangeandbedmaterialsortingisestablishedbyimplicitlytreatingthepbkinEq.
(2)as
andsimultaneouslysolvingthesetofalgebraicequationscorrespondingtoEqs.
(1)-(4)byusingthedirectmethodproposedbyWuandLi(1992).Thiscoupledmethodismorestableandcanmoreeasilyeliminatetheoccurrenceofthecomputednegativebedmaterialgradation,whencomparedtothedecoupledmethod,inwhichthepbkinEq.
(2)istreatedexplicitly.However,theaforementionedcouplingprocedureforsedimenttransport,bedchangeandbedmaterialsortingcomputationsisstilldecoupledfromtheflowcalculation.
ModelParameterstobeAnalyzed
Theparametersinnumericalmodelsofflowandsedimenttransportinriverscanbeclassifiedintotwogroups:
numericalparametersandphysicalparameters.Thenumericalparametersresultfromthediscretizationandsolutionprocedures,whilethephysicalparametersrepresentthephysicalpropertiesofflowandsediment,orthequantitiesderivedfromthemodelingofflowandsedimenttransport.IntheCCHE1Dchannelnetworkmodel,thenumericalparametersincludecomputationtimestepandgridlength,andthephysicalparametersaretheManning’sroughnesscoefficient,non-equilibriumadaptationlengthofsedimenttransport,mixinglayerthickness,bedmaterialporosity,etc.Usually,thenumericalparameterscanbemoreeasilyhandledthanthephysicalparameters.Someofthesephysicalparameters,suchastheManning’sroughnesscoefficientandbedmaterialporosity,havebeenstudiedbymanyinvestigatorsandmaybedeterminedbymeasurement.However,thenon-equilibriumadaptationlengthandthemixinglayerthicknessarelessunderstoodandmustbeprescribedempirically.Therefore,themainconcerninthispaperistoanalyzetheinfluenceofthesetwophysicalparametersonthesimulationresults.
Thenon-equilibriumadaptationlengthLscharacterizesthedistanceforsedimenttoadjustfromanon-equilibriumstatetoanequilibriumstate.Wu,RodiandWenka(2000)andWuandVieira(2000)reviewedindetailthoseempiricalandsemi-empiricalmethodsfordeterminingLspublishedintheliterature,suchasBellandSutherland’s(1981),ArmaninianddiSilvio’s(1988),etc.ItwasfoundthatthosemethodsprovidesignificantlydifferentestimationsofLs.InCCHE1D,theadaptationlengthforwashloadtransportissetasinfinitelylargebecausethenetexchangebetweenwashloadandchannelbedisusuallynegligible.TheadaptationlengthforsuspendedloadtransportiscalculatedwithLs=uh/
ωs,inwhichuisthesection-averagedvelocity,histheflowdepth,ωsisthesettlingvelocityofsedimentparticles,andαistheadaptationcoeficientwhichcanbecalculatedwithArmaninianddiSilvio’s(1988)method,orspecifiedasaconstantvaluebytheuser.Theadaptationlengthforbedloadtransportissuggestedtosetasthelengthofthedominantbedforms,suchas7.3h,thelength
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