水库泥沙淤积的不确定因素分析毕业设计外文翻译Word文件下载.docx

水库泥沙淤积的不确定因素分析毕业设计外文翻译Word文件下载.docx

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Abstract:

Significantadvanceshavebeenmadeinunderstandingtheimportanceofthefactorsinvolvedinreservoirsedimentation.However,predictingtheaccumulationofsedimentinareservoirisstillacomplexproblem.Inestimatingreservoirsedimentationandaccumulation,anumberofuncertaintiesarise.Thesearerelatedtoquantityofstreamflow,sedimentload,sedimentparticlesize,andspecificweight,trapefficiency,andreservoiroperation。

Inthisstudy,MonteCarlosimulationandLatinhypercubesamplingareusedtoquantifytheuncertaintyofannualreservoirsedimentationandaccumulatedreservoirsedimentationthroughtime.Inaddition,sensitivityanalysiswasperformedtoexaminetheimportanceofvariousfactorsontheuncertaintyofannualreservoirsedimentation.TheproposedprocedureshavebeenappliedtotheKennyReservoirattheWhiteRiverBasininColorado.Theuncertaintyofannualreservoirsedimentationandtheeffectofeachuncertainfactor,takenindividuallyandincombinations,ontheuncertaintyofaccumulatedreservoirsedimentationthroughtimehavebeenexamined.Theresultsshowthatannualstreamflowandsedimentloadarethemostimportantfactorsdeterminingthevariabilityofannualreservoirsedimentationandaccumulatedreservoirsedimentation.InthecaseofKennyReservoir,theuncertaintyexpressedbythecoefficientofvariationcanbeontheorderof65%forannualreservoirsedimentationand39%foraccumulatedreservoirsedimentationvolume.

Introduction

Reservoirsedimentationvarieswithseveralfactorssuchassedimentproduction,sedimenttransportationrate,sedimenttype,modeofsedimentdeposition,reservoiroperation,reservoirgeometry,andstreamflowvariability.Sedimentistransportedassuspendedandbedloadsbystreamsandriverscomingintoareservoir.Duetoflowdecelerationwhenariverapproachesareservoir,thesedimenttransportcapacitydecreases,andsomeoftheincomingsedimentistrappedanddepositedinthereservoir.Inaddition,thedepositedsedimentsmayconsolidatebytheirweightandtheweightofoverlyingwaterthroughtime.Predictingthesedimentcomingintoareservoir,itsdeposition,anditsaccumulationthroughouttheyears,afterconstructionofthedam,havebeenimportantproblemsinhydraulicengineering.Despitetheadvancesmadeinunderstandingseveralofthefactorsinvolvedinreservoirsedimentation,predictingtheaccumulationofsedimentinareservoirisstillacomplexproblem.Empiricalmodels,basedonsurveysandfieldobservations,havebeendevelopedandappliedtoestimateannualreservoirsedimentationload（RSL）,accumulatedreservoirsedimentationload,（ARSL）,andaccumulatedreservoirsedimentationvolume（ARSV）afteragivennumberofyearsofreservoiroperation.Likewise,severalmathematicalmodelsforpredictingreservoirsedimentationhavebeendevelopedbasedontheequationsofmotionandcontinuityforwaterandsediment.However,empiricalmethodsarestillwidelyusedinactualengineeringpractice.

Inestimatingresevoirsedimentinflow,reservoirsedimentation,andreservoirsedimentaccumulation,eitherbyempiricaloranalyticalapproaches,anumberofuncertaintiesarises.Themainfactorsaffectingreservoirsedimentationare

（1）quantityofstreamflow;

（2）quantityofsedimentinflowintoareservoir;

（3）sedimentparticlesize;

（4）specificweightofthedeposits;

and（5）reservoirsizeandoperation.Dependingontheparticularcaseathand,somefactorsmaybemoreimportantthanothers.Allofthesefactorsareuncertaintosomedegreeand,asaconsequence,reservoirsedimentationwillbeanuncertainquantitytoo.Inaddition,whichmodel（orprocedure）isapplicabletoestimatesomeoftheforegoingquantitiesand,infact,whichmodelistobeusedtoestimatetheamountofsedimentthatwillbetrappedinareservoirarequestionsthatcannotbeansweredwithcertainty.Forinstance,Fan（1988）obtainedinformationon34stream-,18watershed-,and20reservoir-sedimentationmodelsandstatedthatdifferentmodelsmaygivesignificantlydifferentresultsevenwhenusingthesamesetofinputdata.Suchanadditionalfactor,knownas‘‘modeluncertainty,’’maybequitealargecomponentoftheoveralluncertainty.Inanycase,theplannerandmanagerofareservoirmaybeinterestedinquantifyinghowtheuncertaintyofsomeofthefactorsaffectingreservoirsedimentationtranslateintotheuncertaintyofannualsedimentdepositionandaccumulatedsedimentdepositionthroughtime.Inthispaper,weaddresstheissuequantifyingtheeffectofparameteruncertaintyonreservoirsedimentationbasedonasetofpredefinedmodelsaswillbedescribedbelow.Theeffectofmodeluncertaintyisnotconsideredinthisstudy.

Severalmethodsofuncertaintyanalysishavebeendevelopedandappliedinwaterresourcesengineering.Themostwidelyusedmethodsarefirst-orderanalysis（FOA）andMonteCarlosimulation（MCS）.FOAisbasedonlinearizingthefunctionalrelationshipthatrelatesadependentrandomvariableandasetofindependentrandomvariablesbyTaylorseriesexpansion.Thismethodhasbeenappliedinseveralwaterresourcesandenvironmentalengineeringproblemsinvolvinguncertainty.Examplesincludestormsewerdesign;

ground-water-flowestimation,predictionofdissolvedoxygen;

andsubsurface-flowandcontaminanttransportestimation.InMCS,stochasticinputsaregeneratedfromtheirprobabilitydistributionsandarethenenteredintoempiricaloranalyticalmodelsoftheunderlyingphysicalprocessinvolvedingeneratingstochasticoutputs.Then,thegeneratedoutputsareanalyzedstatisticallytoquantifytheuncertaintyoftheoutput.ManyexamplesofuncertaintyanalysisbyMCScanbefoundinwaterresourcesandenvironmentalengineering.Someexamplesincludesteady-stateground-water-flowestimationandwater-qualitymodeling.Scaviaetal.（1981）madeacomparisonofMCSandFOAfordetermininguncertaintiesassociatedwitheutrophicationmodeloutputssuchasphytoplankton,zooplankton,andnitrogenforms.TheyindicatedthatbothMCSandFOAagreewellinestimatingthemeanandvarianceofmodelestimates.However,MCShastheadvantageofprovidingbetterinformationabouttheoutputfrequencydistribution.

Latinhypercubesampling（LHS）isanalternativesimulationprocedurethathasbeendevelopedforuncertaintyanalysisofphysicalandengineeringsystems.ThebasicideabehindLHSistogeneraterandomstochasticinputsinastratifiedmannerfromtheprobabilitydistributions.InthiswaythenumberofgeneratedinputscanbereducedconsiderablyascomparedtoMCS.TheypointedoutthatthepointestimatemethodyieldsalargermeanandvariancethanthoseobtainedbytheFOAandLHSmethods.Furthermore,instudyingtheimportanceofstochasticinputsontheoutputbysensitivityanalysis,LHSyieldsmoreinformationthantheothertwomethods.

Inthisstudy,uncertaintyanalysisbasedonMCSandLHSmethodsareconductedtoestimatetheprobabilitydistributionofannualreservoirsedimentationvolume（RSV）.Inaddition,sensitivityanalysisisperformedtoseetherelativeimportanceofstochasticinputsinestimatingthevariabilityofRSV.Furthermore,uncertaintyanalysisofARSVthroughouttimeisperformedusingMCS.Inthisprocedure,annualstreamflowsaregeneratedbyastochastictimeseriesmodel.Theeffectofparameteruncertaintyinthestochasticmodelontheoutput（i.e.,ARSV）isalsoconsidered.

EstimationOfAnnualAndAccumulated

ReservoirSedimentLoad（Mass）AndVolume

Reservoirsedimentationvolumedepends,amongotherfactors,onthequantityofsedimentinflow,thepercentageofsedimentinflowtrappedbythereservoir,andthespecificweightofthedepositedsedimentconsideringtheeffectofcompactionwithtime.Theincomingsedimentloadandthestreamflowdischargeareusuallymeasuredathydrometricgaugingstations,andasedimentratingcurveisconstructed.Thesedimentratingcurveexpressestherelationshipbetweentherateofsedimentdischargeandtherateofstreamflowdischargeandisusuallyrepresentedgraphicallyonlogarithmiccoordinates.Incomingsedimentisgenerallycomposedofsuspendedsedimentandbedload.Whenthebedloadcannotbeobtainedbymeasurements,itcanbeestimatedbyformulas.

Inestimatingannualsedimentload,ithasbeencommonpracticetouseannualsedimentratingcurvesforbothsuspendedsedimentandbedload.Theannualsedimentratingcurveistherelationbetweenannualsedimentloadandannualstreamflowdischarge.Twomethodscanbeconsideredfordeterminingannualsedimentratingcurves.Asimplemethodinvolvesthefollowingsteps:

（1）Foragivenyearcalculatedailysedimentloadsfromdailysedimentratingcurves;

（2）addalldailysedimentloadsanddividethesumbythenumberofdaysintheyear,thenthisvaluerepresentstheannualaveragesedimentloadintonsperday;

（3）repeatSteps1and2forallyearsofrecord;

and（4）plottheannualaveragesedimentloadversustheannualaveragestreamflowforeachyearintherecord.Analternativemethodisbasedonestimatingannualsedimentloadsusingflowdurationcurves.Inanycase,anannualsedimentratingcurvecanbeconstructedbysimpleregressionanalysisafterlogarithmictransformationofannualaveragestreamflowdischargesandannualaveragesedimentloads.Colby（1956）statedthatinactualpracticedailysedimentratingcurvescouldbeassumedtobeequivalenttoinstantaneoussedimentratingcurves.

Dailyratingcurvesofsuspendedsedimentandbedloadmayberepresentedas

（1）

（2）

whereQSD=dailysuspendedsedimentload（tons/day）;

QBD=dailybedload（tons/day）;

QWD=dailyaveragestreamflowd