chapter7-环境水文学

'April30,2009PrincipleofHydrology,BNU1Chapter7HydrographAnalysisProf.ZongxueXU April30,2009PrincipleofHydrology,BNU2ObjectivesUnitHydrographT-hourUHInstantaneousUHDimensionlessUHUHtransformationUHApplication April30,2009PrincipleofHydrology,BNU3UnitHydrograph(UH)Definition(Sherman,1932):Ifagivenone-dayrainfallproducesa1-in.depthofrunoffoverthegivendrainagearea,thehydrographshowingtheratesatwhichtherunoffoccurredcanbeconsideredaunitgraphforthatwatershed. April30,2009PrincipleofHydrology,BNU4UnitHydrograph(UH)AnotherdefinitionThehydrographthatresultsfrom1in.ofrainfallexcessgenerateduniformlyoverthewatershedatauniformrateduringaspecifiedperiodoftime. April30,2009PrincipleofHydrology,BNU5BasicAssumptions1in.ofrainfallexcessAuniformspatialdistributionofrainfalloverthewatershedArainfallexcessratethatisconstantwithtimeAspecificdurationofrainfallexcess April30,2009PrincipleofHydrology,BNU6UnitHydrograph(UH)Remarks:Aunithydrographisthehydrographofdirectrunoff(excludingbaseflow)Aunithydrographisproducedby1.0inchofnetrain(thetotalrunoffafterabstractions) April30,2009PrincipleofHydrology,BNU7UHClassificationT-hourUH(TUH)InstantaneousUH(IUH)DimensionlessUH(DUH) April30,2009PrincipleofHydrology,BNU8T-HourUnitHydrographDefinition:Thehydrographthatresultsfromastormwithaconstantdepthofrainfallexcessof1in.overadurationofThours.ExampleA2-hrunithydrographwouldhavea1.0-in.volumeproducedbya2-hrnetrainfall. April30,2009PrincipleofHydrology,BNU9InstantaneousUHDefinitionAspecialcaseoftheT-hourUH,withthedurationofrainfallexcessbeinginfinitesimallysmall April30,2009PrincipleofHydrology,BNU10DimensionlessUHDefinitionAdirect-runoffhydrographwhoseordinatesaregivenasratiosofthepeakdischargeandwhosetimeaxisisdefinedastheratioofthetimetothepeak April30,2009PrincipleofHydrology,BNU11UnitHydrographinChinaTimeperiod:T-hour:1-,3-,6-,12-,24-hour,etc.Unitnetrain:10mm April30,2009PrincipleofHydrology,BNU12ImplicitAssumptionImplicitAssumptioninUHRainfallisdistributedinthesametemporalandspatialpatternforallstorms April30,2009PrincipleofHydrology,BNU13DerivationofUHSelectionofstormsStormsoccurringindividually,thatis,simplestormstructureStormshavinguniformdistributionofrainfallthroughouttheperiodofrainfallexcessStormshavinguniformspatialdistributionovertheentirewatershed April30,2009PrincipleofHydrology,BNU14ConvolutionIntegralU(t):Time-distributedUHx(t):Computedtimedistributionofrainfally(t):Timedistributionofdirectrunoff April30,2009PrincipleofHydrology,BNU15DiscreteFormofConvolutionProcess April30,2009PrincipleofHydrology,BNU16StepstoDevelopUHAnalyzethestreamflowhydrographtopermitseparationofsurfacerunofffrombaseflowEstimatethetotalvolumeofsurfacerunoff(directrunoff)fromthestormproducingtheoriginalhydrograph,theareaunderthehydrographafterbaseflowisremoved April30,2009PrincipleofHydrology,BNU17StepstoDevelopUHDividetheordinatesofthedirectrunoffhydrographbytotaldirectrunoffvolume,andplottheseresultsversustimeasaunitgraphCalculatetheeffectivedurationofrunoff-producingrainforthisunitgraphfromthehyetographofthestormeventused. April30,2009PrincipleofHydrology,BNU18S-Hydrograph April30,2009PrincipleofHydrology,BNU19S-HydrographApplication April30,2009PrincipleofHydrology,BNU20InstantaneousUnitHydrograph(IUH)AnotherdefinitionThehydrographofrunoffthatwouldresultif1in.ofwaterwerespreaduniformlyoveranareainaninstantandthenallowedtorunoff. April30,2009PrincipleofHydrology,BNU21SyntheticUnitHydrographGammadistribution April30,2009PrincipleofHydrology,BNU22HydrographRoutingPurposesPredictthetemporalandspatialvariationsofahydrographasittraversesariverreachorreservoirClassification(physicalprocessequationofmotion)HydrologicapproachHydraulicapproach April30,2009PrincipleofHydrology,BNU23SummariesUnitHydrographUHderivationUHapplication April30,2009PrincipleofHydrology,BNU24Questions&Suggestions? April30,2009PrincipleofHydrology,BNU25SeeYouNextWeek!'