WetlandinundationmodelingofDongtingLakeusingtwodim

ProcediaEnvironmentalSciences13(2012)1091–10981878-0296©2011PublishedbyElsevierB.V.Selectionand/orpeer-reviewunderresponsibilityofSchoolofEnvironment,BeijingNormalUniversity.doi:10.1016/j.proenv.2012.01.102Availableonlineat(2011)1118–1125*,Q.Huang,J.H.JiangStateKeyLaboratoryofLakeScienceandEnvironment,NanjingInstituteofGeography&Limnology,CAS,No.73BeijingEastRoad,Nanjing210008,PRChinaAbstractTounderstandtheinundationprocess(wettinganddrying)inthebottomlandsofDongtingLake,atwo-dimensionalhydrodynamicmodelbasedonshallowwaterequationshasbeendevelopedtomodelcomplexflowregimecontrolledbyboththeYangtzeRiveranditsownbasins.ThegoverningequationsarediscretizedusingthefinitevolumemethodwiththecombinationofquadrilateralandtriangulargridsandthemassandmomentumfluxesaresolvedusingtheapproximateRiemannsolver,HLLCschemewithhighspatialresolution.Theprocessesofwettinganddryingarespeciallytreatedtosimulatetheflowroutingoverdrybed.Verificationshowsthattheproposedmethodcanaccuratelycaptureflowpropagationoverdrybedresultingfromsuddenlybreachofthedam.Thisperformanceispreferredforinundationmodeling.Aftertheoreticaltest,weappliedthemodeltosimulatetheinundationprocessinDongtingLake.Settingthecalibratedroughnessparameters,wesuccessfullysimulatedflowprocessesinthelakefrom2006to2010.Thewaterextentchangesrapidlyalongwiththestagefluctuationinthelake.Indryseason,waterismainlylimitedinchannels,largepartsofbottomlandsareexposedandwaterextentreachestheyearlyminimum.Thewholelakeisinundatedinthefloodseasonandthemaximumofwaterextentreaches.Afterthefloodseason,thebottomlandsexposeagainalongwiththegradualdecreaseofwater.ParticularhydrologicalregimescausetheregularzonaldistributionofvegetationinDongtingLakeWetland.HydrologyinthemiddleYangtzeRiverBasinisundergoinggreatchanges.Thismodelcanbeappliedtoassesspossibleresponsesoflakewetlandforthechangingenvironment.©2011PublishedbyElsevierLtd.Keywords:Wetlandhydrology;Inundationprocess;Hydrodynamicmodel;DongtingLake*Correspondingauthor.Tel.:[phone];fax:[phone].E-mailaddress:[e-mail].©2011PublishedbyElsevierB.V.Selectionand/orpeer-reviewunderresponsibilityofSchoolofEnvironment,BeijingNormalUniversity.1092X.J.Laietal./ProcediaEnvironmentalSciences13(2012)1091–1098X.Laietal./ProcediaEnvironmentalSciences8(2011)1118–112511191.IntroductionPhysicalprocessesofwetland,suchasinundation,greatlyimpactthestructureandfunctionofwetlandecosystem[1].Theyareofcriticalimportanceforthebiogeochemicalandecologicalprocessesinwetlands.Influencedbytheclimatechangesandhumanactivities,regionalhydrologyisexperiencingchanges.Thesechangesdirectlyorindirectlythreatentheecologicalprocessesandcausethesuccessionofvegetationandthenthepossibledamagesofwetlandfunction.Toquantitativelyassesstheresponsesofwetlandchangestothechanginghydrology,in-depthunderstandingandaccuratepredictionofthephysicalprocessesinwetlandareessentialprerequisites.Inundationprocessisoneofimportantphysicalonesofwetland,whichmainlydeterminesthedistributionofwetlandvegetation.Therearemanystudiesforwetlandinundationbasedonthein-situmeasurementandremotesensingdata.Becauseofthelimitationofthedataavailability,suchamethodusuallyhasnosufficientdatawiththedesirabletemporalandspatialresolutionstopredictandassessthechangesofwetland[2].Numericalmodelsaretheefficienttoolstopredicttheinundationprocessofwetland[3].Theycanhelptoquantitativelyanalyzetheresponsesofwetlandecologytoglobalclimatechangesandlocalhumanactivitiesandidentifythecontributionsofthem.However,itisstillachallengefortheaccuratemodelingofinundationprocess,i.e.thewettinganddryinginwetlands.Themodelingoffloodroutingoverdrybedintheinundationmodelingisalsoanopenproblemincomputationalhydraulics.DongtingLakelocatedatthemiddleYangtzeRiverisalargeseasonallylakewithannualstagefluctuationabout12.9m.Theparticularhydrologicalconditionsfosterrichbiodiversityandisrecognizedasanimportanteco-regionforglobalconservation.Inspiteofitsimportance,thealteringofhydrologicalregimeresultingfromthehumanactivities(e.g.theThreeGorgesReservoir,TGR)andglobalclimatechangesisthreateningtheecosystemofwetland.Inthispaper,wehavedevelopedatwo-dimensionalmodelbasedonshallowwaterequationswithaccuratewaterfronttrackingperformance.ThemodelwasappliedtosimulatecomplexinundationprocessinDongtingLake.Thenitsimplicationforwetlandvegetationwasanalyzed.2.Modelingmethod2.1.ShallowwaterequationsWeusethetwo-dimensional(2D)hydrodynamicmodelbasedonshallowwaterequationstosimulatewaterflowsinwetlands.Theconservativeformof2Dshallow-waterequationsareformulatedas:txyFUGUUBU(1)wherexandyareCartesiancoordinates;TTxyhhuhvhqqUisthestatevariablevectoroftheequation(wherehiswaterdepth,anduandvarethevelocitiesinxandydirections,respectively);T220.5huh