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环境水文学chapter9

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环境水文学chapter9

  • 19页
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'June11,2009PrincipleofHydrology,BNU1Chapter9 StatisticalMethodsandFrequencyAnalysisProf.ZongxueXU June11,2009PrincipleofHydrology,BNU2ObjectivesProbability,frequency,returnperiodProbabilitytheoryappliedtohydrologyProbabilitydistributionappliedtohydrologyFrequencyanalysisPearsonTypeIIImethod June11,2009PrincipleofHydrology,BNU3RandomVariablesDefinitionAvariablethatdemonstratesvariabilitythatisnotsufficientlyexplainedbyanalyticalmeasuresofphysicalprocessesExamplesPrecipitationRunoff… June11,2009PrincipleofHydrology,BNU4Continuous/DiscreteRandomVariablesContinuousvariablesRandomvariablesthatmaytakeonallvaluesintherangeofoccurrence,includingfiguresdifferingonlybyaninfinitesimalamountDiscretevariablesRandomvariablesthatarerestrictedtospecific,incrementalvalues June11,2009PrincipleofHydrology,BNU5ProbabilityDistributionDefinitionAgraphofprobabilityinwhichrandomvariables,eithercontinuousordiscrete,arecharacterizedbythedistributionofprobabilitiesattachedtothespecificvaluesthatthevariablemaytakeon. June11,2009PrincipleofHydrology,BNU6CumulativeDistributionFunctionDefinition(CDF)AgraphoftheprobabilitythatanyoutcomeinXislessthanorequaltoastated,limitingvaluex. June11,2009PrincipleofHydrology,BNU7StatisticsMeanVariance/standarddeviationCoefficientofvariationSkewness/Cofficientofskewness June11,2009PrincipleofHydrology,BNU8Mean/VarianceMeanVarianceStandarddeviationsCoefficientofvariation June11,2009PrincipleofHydrology,BNU9CoefficientofSkewnessForsymmetricaldistribution:Cs=0Forrightskewness:Cs>0Forleftskewness:Cs<0 June11,2009PrincipleofHydrology,BNU10ContinuousProbabilityDistributionNormaldistributionLognormaldistributionGammadistribution June11,2009PrincipleofHydrology,BNU11NormalDistributionNormaldistributionStandardnormaldistribution June11,2009PrincipleofHydrology,BNU12LognormalDistribution June11,2009PrincipleofHydrology,BNU13PearsonIIIDistributionPearsonIIIdistributionhasbeenwidelyusedintheflooddesigninChina June11,2009PrincipleofHydrology,BNU14FrequencyAnalysisDefinitionThefrequencyofahydrologiceventistheprobabilitythatsomevalueofadiscretevariablewilloccurorsomevalueofcontinuousvariablewillbeequaledorexceededinanygivenyearMethodsStraightforwardplottingtechniqueFrequencyfactormethod June11,2009PrincipleofHydrology,BNU15PlottingFormulasCaliforniaWeibullChegadayev June11,2009PrincipleofHydrology,BNU16FrequencyAnalysisEvaluatedatahomogeneityRankthedataindescendingmagnitudeCalculateplottingpositionP,andplotthedataonprobabilitygraphpaperCalculatethepopulationstatisticsandplotthecumulativedistributionfunctionComparepopulationstatisticswithregionalvaluesandadjustthefrequencycurveifappropriateSelectpopulationprobabilitydistribution June11,2009PrincipleofHydrology,BNU17SummariesProbabilityStatisticsDistributionFrequencyanalysisPlottingpositionProbabilitygraphpaper June11,2009PrincipleofHydrology,BNU18Questions&Suggestions? June11,2009PrincipleofHydrology,BNU19SeeYouLater!'

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