DOC

A NEW MODEL FOR PREDICTING BED EVOLUTION IN ESTUARINE AREA AND ITS APPLICATION IN YELLOW RIVER DELTA

By Stephen Gonzales,2014-07-05 02:06
8 views 0
A NEW MODEL FOR PREDICTING BED EVOLUTION IN ESTUARINE AREA AND ITS APPLICATION IN YELLOW RIVER DELTA

A NEW MODEL FOR PREDICTING BED

    EVOLUTION IN ESTUARINE AREA AND

    ITS APPLICATION IN YELLOW RIVER

    DELTA

AvaHabIoonlineat’_n{-nIIrc.corn

    ;

    ;‘ScienceDirect

    ;JeumalofHydrodynamics

    ;201l,23(4):457-465

    ;DOI:10.1016/S10016058(10)601369

    ;457

    ;l|}1sciencedifeetcome

    ;sciencournal/lO016058

    ;ANEWMoDELFoRPREDICTINGBEDEVoLUTIoNINESTUAIUNE

    ;AREAANDITSAPPLICATIoNINYELLoWRIVERDELTA

    ;YANGChen,JIANGChunbo

    ;StateKeyLaboratoryofHydroscienceandEngineering,TsinghuaUniversity,Beijing100084,China, ;Email:yangchen07@mails.tsinghua.edu.cn

    ;(ReceivedJanuary6,2011,RevisedFebruary26,2011)

    ;Abstract:Thisarticlediscussestheprocessofsedimenttransportandproposesamorphologica1modeltopredictthebedevolution

    ;inestuaries.Thehydrodynamicmoduleisbasedonanexistentmode1DepthIntegratedVelocityAndS

    oluteTransportrDIVAST)

    ;and

    ewettinganddryingmethodisadoptedtodealwiththemovingboundary.Bothcohesivesedimentandnon.cohesivesediment

    ;aretakenintoconsiderationinthesediment

    ansportmodulewiththecapabilitvofsimulatingthetransportofgradedsediments ;undernon-equilibriumconditions.ThefaIlvelocityofthesuspendedsedimentismodifiedinthepresentmodelduetomehigh

    ;sedimentconcentration.A3-layerapproachisadoptedtosimulatethevariationsofsedimentgradationsofbedmaterials.

    ;Furthermore,themodelisusedtosimulatethebedevolutionintheYellowRiverDeltafYRD1from1992to1995.Fielddataare

    ;usedtocalibratetheparameters.ThenumericalresultsshowhowthemorphologywasdevelopedintheYellowRiverEstuarywitha

;goodagreementwiththefielddata.

    ;Keywords:bedevolution,gradedsediments,morphology,numericalmodel,sedimenttransport,Yello

    wRiverDelta(YRD)

    ;Introduetion

    ;Thewaterbodiesinestuariesfeatureashallow ;waterdepth,acomplicatedgeometryandarather ;gradedsediment.Theinteractionamongthefluid ;flows,thesedimenttransportandthebedlevel ;changesisofgreatimportancetosomewaterenviro- ;nmentalissuesandrivermouthwetlandfunctions. ;Themotionofthesediment

    ;cularcharacteristics,suchas

    ;isrelatedwithitsparti

    ;cohesiveandnon..cohe..

    ;siveproperties,whichplayimportantrolesinthe ;longtermbedevolution.Inthepastdecades,thebed ;evolutionprocessinestuarineandcoastalbasinswas ;extensivelyinvestigatedbothexperimentallyand ;numerically.Schramkowskieta1.analyzedthe

    ;effectsofgeometryandbottomfrictiononlocalbed ;formsinatidalembayment.Intheirstudy.thewater ;motionwasmodeledbyusingthedepthaveraged

    ;ProjectsupportedbytheKeyProjectofNationalNatural ;ScienceFoundationofChina(GrantNo.51039002),theState ;KeyLaboratoryofHydroscienceandEngineering, ;Tsinghua

    ;Unive~ity(GrantNo.2009TC.2,.

    ;Biography:YANGChen(1981.1,Male,Ph.D. ;C0rrespOnding:JIANGChun.bO.

    ;E-mail:job@mail.tsinghua.edu.cn

    ;shallowwaterequationsanddrivenbyanexternally ;prescribedM,tide.takingaccountoftheansportof

    ;thesuspendedload.ZhangandLiudevelopeda ;numericalmodeltosimulatethesuspendedsediment ;transport,builtintheverticalo-coordinatefor ;fittingthefreesurfaceandbottom,andanalyzedvari

    ;OUSparameters,inwhichtheeddydiffusion.thefa11 ;velocityandtheRousenumberarefoundtobethe ;predominantfactorsofthesedimenttransport.Chung ;andEppelinvestigatedthesensitivityofsediment ;transportandbedmorphologywithrespecttothebed ;slopeandgrainsize,andthenonhvdrostaticpressure

    ;termwastreatedthroughnumericalsimulationsbased ;ona3Dhydrodynamicandsedimenttransportmode1.

    ;Taneta1.studiedtheerosionprocessofcohesive ;sedimentafterconsolidationexperimentallyina ;closedconduitsystemandderivedascourratefor. ;mulabasedontheexperimentalresults.Lidevelo.

    ;pednumericalmodelsoftidalcurrentandsediment ;movementunderthecombinedactionofwaveand ;currentwithanirregulartriangulargrid,carriedout ;numericalsimulations,andtheeffectofreclamationin ;0ujiangEstuarywasanalyzedbythemodels. ;TheYellowRiverDeltafYRD)islocatedina ;jointzoneofYellowRiverandBohaiSea.andisthe ;baseofenergysources,petroleumandagricultureof ;蠹一

    ;458

    ;ShandongProvinceofChina.TheYellowRiverhas ;thehighestsedimentconcentrationintheworld. ;whichtakesnearly10tofsedimenttotheYRDand ;BohaiSeaeveryyear_)J.Becauseoftheweaktidein

    ;BohaiBaythetidecurrentcanonlytake1/3ofthe ;sedimentintotheoutersea.somostofthesedimentis ;heldupattherivermouthandmakethetopographyof ;theYRDgreatlychangableallthetime.

    ;Withrespecttothenumericalinvestigationsof ;theYellowRiver.Zhangeta1.developeda1.D

    ;modelforunsteadysedimenttransportintheNingxia ;reachoftheYellowRiver.thecOncentrationdistri

    ;butionsandthemeandiameterdistributionsofSHS

    ;pendedsedimentinthetransversa1directionwerealso ;estimatedbyusingthismodel,andaftervalidation ;themodelwasusedtopredicttheriverbeddefor

    ;marionduringtheperiodofl9992019intheNingxia

    ;reachoftheYellowRiver.Caoeta1.Lestablisheda ;2Dnumericalmodelbasedon”slotmethod”forun—

    ;steadyflowandsedimenttransportandeffectively ;simulatedthesedimenttransport,scouringandsilting ;ofseabedandthevariationofcoastline.Lieta1.

    ;builta2.DmodelbasedontheVplumeOfFluid ;(VOF1techniqueandapplieditinPaniiataiShoal,one ;oftheimportantreachesintheYellowRiver.Zhaoet ;a1.…derivedaset0fnew2.Dequationsforinter—

    ;changesbetweensuspendedsedimentandbedmate

    ;rialsbasedonrelatedstudiesfortheLowerYellow ;River.Kongeta1.appliedtheEnvironmentalFluid

    ;DynamicsCode(EFDC,codetosimulatethebed

    ;evolutionprocessintheYRDfrom1992to2000and ;obtainedsomereasonableresults.

    ;Inthepresentstudy.a2Ddepth.integrated

    ;numericalmodelisdevelopedtopredictthehydro

    ;dynamic,sedimenttransportandmorphologicalpro

    ;cessesintheYRD.Themodelhastheabilityto ;simulatethetransportofgradedsedimentsundernon

    ;equilibriumconditions.Thebedmixtureisdivided ;intofractions.withconsideratiOnofboththecohesive ;sedimentandthenoncohesivesediment,andeach

    ;fractionofsedimentissimulatedseparatelybyassu

    ;mingthatthefractionsdonotinteractwitheachother ;inthewaterbody.Theevolutionofthebedisthe ;resultoferosionorsedimentation.Inordertoaccount ;f0rtheinfluenceofbedsedimentcompositiononthe ;overalltransportprocessamethodofmultiplebed ;layersisusedtorepresentthespatialandtemporal ;variationsofsedimentgradationsofthelposebed ;layers.Inviewofthehighsedimentconcentrationof ;YellowRiver.thefallvelocityofthesuspendedsedi

    ;mentiSmodifiedinthepresentmodelaccordingtothe ;practicalsedimentconcentration.Thepresentmodelis ;usedtosimulatethebedevolutionintheYRDfrom ;1992tol995.andthenumericalpredictionsbythe ;presentmodelarecomparedwithexperimentalmea

    ;surementsandthepredictionsbasedonnonfractional

    ;mode1s.

    ;1.Numericalmodeldetails

    ;1.1Governingequationsforhydrodynamicprocess ;Thehydrodynamicmodelforpredictingthe ;waterelevationandvelocityfieldsincoasta1.estua

    ;rineandriverinewatersinvolvesthesolutionofthe ;governingequationsoffluidflow.The2Dhydro

    ;dynamicequationsaregenerallybasedonthedepth

    ;integrated3DReynoldsequationsforincompressible ;andunsteadyturbulentflows.withcOnsiderationsof ;theeffectsoftheearth’srotation,bottomfrictionand

    ;windshear.Thehydrodynamicmoduleinthepresent ;modelisbasedonanexistentmodelDepthIntegrated

    ;VelocityAndSoluteTransportrDIVAST).withits ;capacityindealingwiththefloodinganddryingpro

    ;cessesasausefulfeature.Moredetailsofthehydro ;dynamicgoverningequationsandsolutionmethods ;canbefoundinFalconer’sarticlellz1.

    ;1.2Governimzequationsforsealimenttianspot, ;Proeess

    ;Inestuarineandcoastalwaters.thesedimentsare ;usuallyhighlygraded,rangingfromveryfinetorather ;coarseparticles.Thetransportpropertiesofsuchsedi

    ;mentsmayvarysignificantly.Thusinsomesituations ;itwouldnotbereasonabletouseasinglediameterto ;represental1sediments.Inthepresentstudy,the ;gradedsedimentisdividedintoNfractionsacco

    ;rdingtotheparticlesizedistribution. ;Itiswidelyacceptedthatthesuspendedsediment ;concentrationcanbedescribedbytheadvective

    ;diffusionequation.Forhorizontalorquasihorizontal

    ;flows.the3.Dsolutemassbalanceequationcanbe ;integratedoverthewaterdepthtoobtainthe2D

    ;depth.integratedadvectivediffusionequation,as

    ;+

    ;OHU

    ;

    ;@+:fD+

    ;Ot3x(f

    ;H

    ;]+DyxOx+.-av)]+,

    ;(1)

    ;whereisthedepthaveragedsuspendedsediment ;concentrationfortheith(i=1,2…?)fraction,D,

    ;D,Darethedepthaverageddiffusion

    ;coefficientsinthexanddirections.S,isasource ;termforthethfractionwhichrepresentstheerosion ;anddepositionfluxes.

    ;Incoastalandestuarinewaters,thewaterdepthH ;mayvarygreatly,thusthemonotonicityofthedepth ;integratedconcentration(0,H)maybedifferentfrom ;thatofthesoluteconcentration().Inordertoachi ;eveahighaccuracyandthemassconservation,Eq.(1) ;couldberecastwithanadditionalsourcetermbeing ;introducedintothe2Ddepthintegratedadvective

    ;diffusionequation.Inthecurrentstudy,thismodifica_ ;tionisincludedinthesedimenttransportequation, ;i.e.,

    ;3t+O

    ;x

    ;+=

    ;H(Ox+ay\

;D.H

    ;)+吉专-gx+]+

    ;S+Sdi(2)

    ;whereSmistheadditionalsourcetermfortheith ;fraction,whichcanbeformulatedintheformas ;+

    ;](3)

    ;Theadditionalsourcetermisshowntobevital ;forthemassconservationinmodellingmassand ;solutetransport.

    ;Forcohesivesediment<0.063mm),where ;disthesedimentparticlediameter,finEq.(2) ;canbeobtainedas

    ;i-Ei-D~(4)

    ;whereDiisthedepositionalfluxandistheero

    ;sionflux,whosemostwidelyusedexpressionsare[]: ;D/=wsirbi<Z’cd

    ;0,>

    ;E.=

    ;(/l

    ;0,?Le

    ;i>

    ;(5a)

    ;(5b)

    ;(6a)

    ;459

    ;abouttheparameterscouldbefoundinWinterwerp ;andVanKesteren.

    ;Fornon.cohesivesediment,Sscanbeobtained ;as

    ;[14]

    ;(0a)

    ;H

    ;(7)

    ;whereisthesedimentconcentrationforthefth ;fractionatareferencelevel”a”nearthebed.and

    ;

    ;istheequilibriumsedimentconcentrationforsize ;fractionatthereferenceleve1.Thefallvelocity ;wwillbegreatlyreducedwhenthesedimentcon- ;centrationislargerthan10000mg/1.whichiscalled ;thehinderedsettling.Theseeffectsareincorporatedin ;thefollowingrelationshipforthesettlingvelocityJ ;

;(8)

    ;wherePsisthesedimentdensity,isacoefficient ;forthenormalflowcondition,whichtakesavalueof ;about415].

    ;Forequilibriumsuspendedsedimentfluxes, ;f=and0.Thereferencelevel”a”is

    ;equaltotheequivalentroughnessheightwitha ;minimumvalueofa=0.01.

    ;Theexpressionusedinthisstudytodefne ;followsfromVanRijn[anditiswrittenas ;~aei=0.0i5D

    ;n

    ;S~i

    ;T

    ;U

    ;/

    ;I’5

    ;(9)

    ;where0fisthemediangrainsizeforthefIhfra

    ;ction,putisthepercentageoftheithfractioninthe ;looselayerofbed,isthedimensionlessparticle ;sizeandisthetransportstageparameterforthefth ;fraction.

    ;Inadepthintegrated2Dmode1.onlythemean

    ;sedimentconcentrationisconsidered.Hencethe

    ;(6b)valueofthereference

    ;wherewisthefa11velocityofsedimentparticle, ;fbistheflowinducedbedshearstress,cdandce ;arethecriticalshearstressesfordepositionandero. ;sion,respectively,isthenearsedimentconcentra

    ;tion,Mistheerosionparameterwhichshouldvary ;withtimeanddepthbutisgenerallyassumedasa ;constant.Theexponent/70isgenerallyunity.Details ;foreberelatedtothe

    ;whichisassumedtobe

    ;

    ;0e

    ;concentrationmustthere-

    ;depthmeanconcentration0/,

    ;inthefollowingform[]

    ;(10)

    ;wherefisthedepthmeanequilibriumconcentra- ;tion.CombiningEqs.(7)and(10),oneobtainsthe ;460

    ;followingneterosionordepositionrate ;where

    ;W

    ;s(一妒

    ;H

    ;Thedepthmeanequilibriumconcentration ;cannowbecalculatedfromtheratioofthedepthinte

    ;gratedequilibriumsuspendedsedimentfluxqto ;thedepthintegratedfluidfluxq,as ;=

    ;g

    ;inwhicht2”isaprofilefactor,beingassumedtobe

    ;1.131.

    ;SuspensionDepositionFlow

    ;Il…

    ;L

    ;PTHT

    ;Toplayer

    ;r

    ;P?HM

    ;Middlelayer1r

    ;Pfl//L

    ;Bottomlayer1

    ;Fig.1Bedsedimentlayers

    ;?

    ;1.3Bedlevelchange

    ;Foreachfractionofthecohesivesediment,the ;correspondingbedelevationchangeduringAtcan ;bedeterminedby

    ;l~kZBi

    ;

    ;1(Ei)0(13)

    ;Foreachfractionofthenoncohesivesediment,the ;correspondingbedelevationchangeduringAtcan ;beobtainedfromtheequation

    ;aZBi

    ;

    ;1().(14)

    ;whereP0istheporosityofthebedlayersediment. ;Withinatimestep,thetotalvariationofthebedlevel

    ;B

    ;isobtainedas

    ;AZ

    ;1.4Bedsedimentsizevariation

    ;Thedeformationofthebed.especiallyduringthe ;degradingprocess.iSdominantlycontrolledbythe ;compositionofthebedmateria1.Thescouredbed ;tendstobearmouredtopreventfurthererosionorto ;becomerefinedinthecaseofdeposition.Toaccount ;fortheinfluenceofthebedsedimentcomposition, ;numericalmodelsweredevelopedtosolvethespatial ;andtemporalvariationsofthesedimentgradationof ;theloosebedlayers.Thiscanbedonebydividingthe ;loosesedimentbedintosevera1vertica1layers.AS ;showninFig.1.theloosebediSdividedintothetop ;middleandbottomlayerswiththethicknessand ;volumetricfractionsofthese1ayersbeingdefinedas ;HT,HM,HLandPTl,PMl,Pl_Irespectively. ;Thesuperscript0indicatesthevaluesoflasttimestep. ;x/kn

    ;Fig.2LocationofYellowRiverEstuary

    ;Table1Averagefractionaldiametersandcorresponding ;Duetoerosionordeposition,thefractionper

    ;centageofthetoplayerHr+AZduringasmall

    ;timeinterva1canbeobtainedas

    ;HTl

    ;AZB

    ;HT+AZB

    ;whereAZisthescouredordepositedthicknessoi ;?

    ;?

    ;

    ;anindividualsedimentfraction

    ;4000

    ;3000

    ;2000

    ;l000

    ;0

    ;0500l500

    ;t/d

    ;Fig.3InflowfluxatLijinStationfrom1992to2000 ;120000

    ;80000

    ;4OooO

    ;0

    ;050010001500

    ;t/d

    ;Fig.4SedimentconcentrationinLijinStationfrom1992to

;2000

    ;Inthecaseofdeposition,i.e.,AZB>0,the ;fractionpercentageofthetoplayeriscalculatedby ;Eq.(16).Thefractionpercentageofthemiddlelayer ;canbecalculatedas

    ;,AZB?Hr(17a)

    ;:

    ;AZ.PT,+(/-/

    ;T-AZ.)P~i

    ;,?Z<(17b)LH

    ;M

    ;B…T

    ;Thefractionpercentageofthebottomlayercan ;becalculatedas

    ;,?Z

    ;Hl+uj

    ;

    ;AZ

    ;

    ;B

    ;P

    ;

    ;Mi

    ;_

    ;+

    ;

    ;HLPL~

    ;i

    ;,?<

    ;HL+AZB

    ;(18a)

    ;(18b)

    ;Ontheotherhand,inthecaseoferosion,i.e., ;AZ<0,thepositionofthetoplayershouldbe ;adjusted.Theadjustedfractionpercentageofthetop ;layercanbecalculatedas

    ;=f19)

    ;Thefractionpercentageofthemiddlelayercanbe ;calculatedas

    ;=

    ;46l

    ;(2O)

    ;Thefractionpercentageofthebottomlayerkeeps ;unchanged,butthethicknessofthelowerlayeris

Report this document

For any questions or suggestions please email
cust-service@docsford.com