水文学原理PPT课件

.,1,PhysicalHydrology,S.LawrenceDingman,.,2,WhoamI?,ZhangXiang68772303-601(office:0101609zhangxiang,.,3,Textbookandreferences,TextbookPhysicalHydrologyReferencesHydrologyforEngineersbyR.K.LinsleyHydrology:principles,analysisanddesignbyH.M.RaghunathHydrology:anintroductiontohydrologicsciencebyR.L.Bras水文学原理(一)胡方荣候宇光水文学原理(二)于维忠水文学原理芮孝芳,.,4,TimeArrange,Lecture:36classhourspart1and2:4classhourspart4:8classhourspart6:8classhourspart7:6classhourspart8:6classhourspart9:4classhoursLab:6classhoursforcomputer,.,5,TheFinals,Assignments(30%)Checkingonattendance(20%)Examination(50%),.,6,Attention!,Prepareyourcoursebeforehandwords,sentences,phasesNoabsenceisallowedDontbelateforclassReadasmuchaspossible,writeasmuchaspossible,usetheInternetforhelpasmuchaspossible,.,7,1IntroductiontoHydrologicScience,DEFINITIONANDSCOPEOFHYDROLOGYDEVELOPMENTOFSCENTIFICHYDROLOGYAPPROACHANDSCOPEOFTHISBOOK,.,8,1.1DEFFINTIONANDSCOPEOFHYDROLOGY,.,9,Hydrologyisbroadlydefinedasthegeosciencethatdes-cribeandpredictstheoccurrence,circulation,anddistri-butionofthewateroftheearthanditsatmosphere.TheglobalhydrologiccycleThelandphaseofthehydrologiccycle,.,10,WaterCycle,.,11,.,12,.,13,.,14,InterdisciplinaryScienceTomanagewaterresourcesandwaterrelatedhazardsEngineeringhydrology,economicsandrelatedsocialscienceforwater-resourcesmanagement,.,15,1.2DEVELOPMENTOFSCIENTIFICHYDROLOGY,5000-6000B.P.Pakistan,China,Egypt：Canals,levees,dam,well3800B.P.Egyptians:monitoringofriverflow2400B.PIndia:rainfallmeasurement,.,16,Theconceptofaglobalhydrologycycledatesfromatleast3000P.B(Nace1974),whenSolomonwroteinEcclesiastes1:7thatAlltheriversrunintothesea;yettheseaisnotfull;untotheplacefromwhencetheriverscome,thithertheyreturnagain.The18thcenturysawconsiderableadvanceinapplicationsofmathematicstofluidmechanicsandhydraulicsbyPitot,BeroulliChezy,Euler,andothersinEurope.Useofterm“hydrology”inapproximatelyitscurrentmeaningbeganabout1750.,.,17,Treatisesonvariousaspectsofhydrology,beginningwiththeEnglishmanNathanielBeard-moresManualofHydrologyin1862,appearedwithincreasingfrequ-encyinthelasthalfofthe19thcentury.Thehalfofthetwentiethcenturysawgreatprogressinmanyaspectofhydrologyand,withtheformationoftheSectionofScientificHydrologyintheInternationalUnionofGeodesyandGeophysics(IUGG,1992)andHydrologySectionoftheAmericanGeophysicalUnion(1930),thefirstformrecognitionofthescientificstatusofhydrology.,.,18,Thereare,infactgreatopportunitiesforprogressinphysicalhy-drologyinmanyareas,includingthedeterminationofregionalevapotranspirationrate,themovementofgroundwaterinrockfracture,therelationbetweenhydrologybehavioratdifferentscales,there-lationofhydrologyregimestopastandfutureclimatesandtheinteractionofhydrologyprocessesandland-formdevelopment(Eaglesonetal.1991).,.,19,Theabilitytounderstandandmodelhydrologicprocessesatcontinentalandglobalscaleisbe-comeincreasingimpor-tantbecauseoftheneedtopredicttheeffectsoflarge-scalechangesinlandandinclimate.FrompointtolargerInthelandphaseofthehydrologiccycle,itisinterestingthatdetailedfieldstudiestounderstandthemechanismsbywhichwaterentersstreamsbegantoproliferateonlyinthe1960s,pioneeredbyT.Dunneandothers.Thetemporalandspatialvariabilityofnaturalconditions,.,20,2BasicHydrologicConcepts,2.1PHYSICALQUANTITIESANDLAWS2.2HYDROLOGICSYSTEMS2.3THECONSERVATIONEQUATIONS2.4THEWATERSHED(DRAINAGEBASIN)2.5THEREGIONALWATERBALANCE2.6SPATIALVARIABILITY2.7TEMPORALVARIABILITY2.8STORAGE,STORAGEEFFECTS,ANDRESIDENCETIME,.,21,2.1PHYSICALQUNTITESANDLAWS,Hydrologyisaquantitygeophysicalscience,Inprinciple,thesenumericalvaluesofhydrologicvaluesaredeterminedbyeither1.counting,inwhichcasethequantitytakesonavaluethatisapositiveintegerorzero;or2.Measuring,inwhichcasethequantitytakesonavaluecorrespondingtoapointontherealnumberscalethatistheratioofthemagnitudeofthequantitytothemagnitudeofastandardunitofmeasurement.,.,22,Thebasicrelationsofphysicalhydrologyarederivedformfundamentallawsofclassicphysics,particularlythoselistedinTable2-1.,.,23,2.2HYHDROLOGICSYSTEM,SeveralbasichydrologicconceptsarerelatedtothesimplemodelofasystemshowninFigure2-1.TheouterdashedlineinFigure2-1indicatesthatanygroupoflinkedsystemscanbeaggregatedintoalargersystem;thesmallersystemscouldthenbecalledsubsystems.,.,24,.,25,2.3THECONSERVATIONEQUATIONS,Theamountofaconservativequantityenteringacontrolvolumeduringadefinedtimeperiod,minustheamountofthequantityleavingthevolumeduringthetimeperiod,equalsthechangeintheamountofthequantitystoredinthevolumeduringthetimeperiod.,.,26,(2-2),(2-3),AmountInAmountout=ChangeInstorage,(2-1),.,27,(2-4),(2-5),(2-6),.,28,Anotherversionoftheconservationequationcanbedevelopedbydefiningtheinstantaneousratesofinflow,i,andoutflow,q,as,(2-7),(2-8),(2-9),.,29,Equations(2-2),(2-6),and(2-9),arecalledwater-balanceequa-tionwhenappliedtothemassofwatermovingthroughvariousportionsofthehydrologiccycle;controlvolumesintheseappli-cationsrangeinsizefrominfinitesimaltoannualorlonger(Figure1-3).evaporationandsnowmeltenergy-balancetheconservationofmomentumfluidflow,.,30,2.4THEWATERSHED(DRAINAGEBASIN),Watershed(alsocalleddrainagebasin,riverbasin,orcatch-ment),definedastheareathatappearsonthebasisoftopographytocontributeallthewaterthatpass-esthroughagivencrosssectionofastream(Figure2-2).dividedrainagearea,2.4.1definition,.,31,.,32,Thusthewatershedcanbeviewedasanaturallandscapeunit,integratedbywaterflowingthroughthelandphaseofthehydr-ologiccycleand,althoughpoliticalboundariesdonotgenerallyfollowwatershedboundaries,water-resourceandland-useplanningagenciesrecognizethateffectivemanagementofwaterqualityandqualityrequireawatershedperspective.Thelocationofthestreamcrosssectionthatdefinesthewater-shedisdeterminedbythepurposeoftheanalysis.,.,33,Theconventionalmanualmethodofwatershedde-lineationrequiresatopographicmap(orstereo-scopicallyviewedaerialphotographs).Increasingly,topographicinformationisbecomingavailableintheformofdigitalelevationmodels(DEMs).Thisautomatedapproachtowatersheddelineationallowstheconcomitantrapidextractionofmuchhydrologicallyusefulinformationonwatershedcharacteristics(suchasthedistri-butionofelevationandslop)thatpreviouslycouldbeobtainedonlybyverytediousmanualmethods.,2.4.2Delineation,.,34,2.5THEREGIONALWATERBALANCE,Theregionalwaterbalanceistheapplicationofthewater-balanceequationtoawatershed(ortoanylandarea,suchasastateorcontinent).,.,35,2.5.1TheWater-BalanceEquation,.,36,(2-10),Ifweaveragethesequantitiesoverareasonablylongtimeperiod(say,manyyears)inwhichtherearenosignificantclimatictrendsorgeologicalchangesandnoanthropogenicinputs,orstoragemodifications,wecanusuallyassumethatnetchangeinstoragewillbeeffectivelyzeroandwritethewaterbalanceas,(2-11),.,37,runoff,RO;hydrologicproduction;,(2-12),(2-13),.,38,(2-14),Whenweassumethat,isnegligibleandwritethewater-balance,equationas,(2-15),.,39,Bothprecipitationandevaportranspirationcanbeconsideredtobeexternallyimposedclimaticboundaryconditions.This,fromEquation(2-15),runoffisaresidualordifferencebetweentwoclimatically-determinedquantities.2.5.2EstimationofRegionalEvaportranspirationPerhapsthemostcommonformofhydrologicanalysisistheestimationofthelong-termaveragevalueofregionalevapor-transpirationviathewater-balanceequation.,.,40,Itisusuallyassumedthatground-waterflowseitherarenegligibleorcanceloutandthatisnegligible,sothatequation(2-15)becomes,(2-16),Modelerror,whichreferstotheomissionofpotentiallysignifi-canttermformtheequation,andmeasurementinthequantitiesand,whichisunavoidable.,.,41,Ground-waterFlowsStreamsdraininglargerwatershedstendtoreceivethesubsur-faceoutflowsoftheirsmallerconstituentwatershed,sotheimportanceofground-waterout-flowgenerallydecreaseasoneconsiderslargerandlargerwatershed.,.,42,StorageChangeHydrologistsattempttominimizeitsvalueby(1)us-inglongmeasurementperiodsanda(2)selectingthetimeofbeginningandendofthemeasurementperiodsuchthatstoragevaluesarelikelytobenearlyequal.,.,43,MeasurementErrorAccuracyofRegionalPrecipitationValuesindividualgagesarealaveragesInregionsofthehighrelieforwithfeworpoorlydistributedgages,orforshortermeasurementperi-ods,theuncertainlycanbeconsiderablylarger.,.,44,AccuracyofStreamflowValuesWinter(1981)estimatedthatthemeasurementun-certainlyforlong-termaveragevaluesofstreamflowatagagingstationisontheorderof.(Theac-curacyofsuchmeasurementsisdiscussedfurtherinSectionF.2.4)whereisestimatedforlocationsothercarefullymaintainedgagingstations,theuncertaintycanbemuchgreater.,.,45,Potentialmeasurementerrorsareusuallyassumedtobedistri-butedsymmetricallyaboutthetruevalue(equalchanceofunder-orover-estimation)andtofollowthebell-shapednormaldistributiondescribeinAppendixC:thefutureameasuredvalueisfromthetruevalue(i.e.,thelargeristheerror),thesmallisprobabilitythatitwilloccur(Figure2-4).Thespread,orvariation,ofthepotentialmeasuredvaluesaboutthetruevalueisexpressedasthestandarddeviationofthepotentialerrors.,.,46,Thestandarddeviationsoftheerrorsduetomeasurementofthequantitiesarerelatedas,(2-17),“Iam100.p%surethatthetruevalueofprecipitationiswithinofthemeasuredvalue.”(2-18a),.,47,istheestimateofaverageprecipitationandistherelativeuncertaintyintheestimate(e.g,ifthemeasurementuncertaintyisstatedtobe10%,=0.1).Theabsoluteuncer-taintyinis.,(2-18b),.,48,Giventhatpotentialmeasurementerrorsfollowthenormaldistribution,wecanfindfromthepropertiesofthatdistribution,summarizedinTableC-5,thatthereisa95%probabilitythatanobservationwillbewithin1.96standarddeviationsofthecentral(true)value.,(2-19),.,49,(2-20),(2-21a),(2-21b),.,50,(2-22),(2-23),Assumetherelativemeasurementerrorsforprecipitationandstreamfloware=0.1and=0.05.,.,51,2.6SPATIALVARIABILITY,However,precipitationgagesareusuallyunevenlydistributedoveranygivenregion,andthepointvaluesarethereforeanun-representativesampleofthetrueprecipitationfield,Becauseofthis,andbecauseoftheimportanceofaccuratelyquantifyingvariablessuchasprecipitation,basicstatisticalconceptshavebeenincorporatedintospecialtechniqueforcharacterizingandaccountingforspatialvariability.,.,52,2.7TEMPORALVARIABILITY,Theinputs,storagesandoutputsinFigurearealltime-distributedvariablesquantitiesthatcanvarywithtime.Inparticular,thestreamflowrateatagivenlocationishighlyvariableintime.Fromthehumanviewpoint,thelong-termaveragestreamflowrate,ishighlysignificant:itrepresentsthemaximumrateatwhichwaterispotentiallyavailableforhumanuseandmanagement,andisthereforeameasureoftheultimatewaterresourcesofawatershedorregion.,.,53,Streamflowvariabilityisdirectlyrelatedtotheseasonalandinterannualvariabilityofrunoff(andhenceoftheclimateofprecipitationandevapo-transpiration)andinverselytotheamountofsto-rageinthewatershed.Humancanincreasewateravailabilitybybuildingstoragereservoirs,asdis-cussedinSection2.8and10.2.5.Humancanalsoattempttoincreasethrough“rain-making”(Sec-tion4.4.5)andtodecreasebymodifyingvegeta-tion(Section7.6.4and10.2.5).Thebasicapproachforconstructingandanalyzingsampleoftine-distributedvariables.,.,54,Eachvalueofwhichisassociatedwithaparticulartimeinasequencetimes,.Suchasequenceiscalledatimeseries.Sometime-seriesvariablesareobtainedbycountingforexample,thenumberofdayswithmorethan1mmrainineachyearataparticularlocation.Suchvariablesareinherentlydiscrete.Continuoustimetrace:theytakeonvaluesateveryinstantintime.,2.7.1TimeSeries,.,55,.,56,EXAMPLE2-2Table2-2lists,andFigure2-6plots,threetimeseriesdevelopedfromthecontinuousstreamflowrecordobtainatthestreamgagingstationoperatedbytheU.S.GeologicalSurveyontheOysterRiverinDurham,NH.Inallthreeplots,=1yr,andtheordinateisastreamflowrate,ordis-charge,However,thediscretizationofthecontinuousrecordwasdonedifferentlyforeachseries:Se-riesaistheaveragestreamflowfortheyear,seriesbisthehigh-estinstantaneousflowratesfortheyear,seriescisthelowestoftheflowratesfoundbyaveragingoverseven-consecutive-dayperiodswithineachyear.(Thesedataarealsointhespreadsheetfiletable2-2,xlsonthediskaccompanyingthistext.)Notethatthelinesconnectingthetime-seriesvaluesineachgraphdonotrepresentatimetracetheyserveonlytoconnectthepointvaluetoprovideavisualtoprovideimpressionofthenatureoftheseries.,.,57,.,58,Timeseriesareusuallytreatedasmoreorlessrepresentativesampleofthelong-termbehavioro