Chapter7-环境水文学.ppt

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1、April 30,2009Principle of Hydrology,BNU1Chapter 7 Chapter 7 Hydrograph Hydrograph AnalysisAnalysisProf.Zongxue XUProf.Zongxue XUApril 30,2009Principle of Hydrology,BNU2ObjectivesUnit HydrographT-hour UHInstantaneous UHDimensionless UHUH transformationUH ApplicationApril 30,2009Principle of Hydrology

2、,BNU3Unit Hydrograph(UH)Definition(Sherman,1932):If a given one-day rainfall produces a 1-in.depth of runoff over the given drainage area,the hydrograph showing the rates at which the runoff occurred can be considered a unit graph for that watershed.April 30,2009Principle of Hydrology,BNU4Unit Hydro

3、graph(UH)Another definitionThe hydrograph that results from 1 in.of rainfall excess generated uniformly over the watershed at a uniform rate during a specified period of time.April 30,2009Principle of Hydrology,BNU5Basic Assumptions1.1 in.of rainfall excess2.A uniform spatial distribution of rainfal

4、l over the watershed3.A rainfall excess rate that is constant with time4.A specific duration of rainfall excessApril 30,2009Principle of Hydrology,BNU6Unit Hydrograph(UH)Remarks:A unit hydrograph is the hydrograph of direct runoff(excluding base flow)A unit hydrograph is produced by 1.0 inch of net

5、rain(the total runoff after abstractions)April 30,2009Principle of Hydrology,BNU7UH ClassificationT-hour UH(TUH)Instantaneous UH(IUH)Dimensionless UH(DUH)April 30,2009Principle of Hydrology,BNU8T-Hour Unit HydrographDefinition:The hydrograph that results from a storm with a constant depth of rainfal

6、l excess of 1 in.over a duration of T hours.ExampleA 2-hr unit hydrograph would have a 1.0-in.volume produced by a 2-hr net rainfall.April 30,2009Principle of Hydrology,BNU9Instantaneous UHDefinitionA special case of the T-hour UH,with the duration of rainfall excess being infinitesimally smallApril

7、 30,2009Principle of Hydrology,BNU10Dimensionless UHDefinitionA direct-runoff hydrograph whose ordinates are given as ratios of the peak discharge and whose time axis is defined as the ratio of the time to the peakApril 30,2009Principle of Hydrology,BNU11Unit Hydrograph in ChinaTime period:T-hour:1-

8、,3-,6-,12-,24-hour,etc.Unit net rain:10 mmApril 30,2009Principle of Hydrology,BNU12Implicit AssumptionImplicit Assumption in UHRainfall is distributed in the same temporal and spatial pattern for all stormsApril 30,2009Principle of Hydrology,BNU13Derivation of UHSelection of stormsStorms occurring i

9、ndividually,that is,simple storm structureStorms having uniform distribution of rainfall throughout the period of rainfall excessStorms having uniform spatial distribution over the entire watershedApril 30,2009Principle of Hydrology,BNU14Convolution IntegralU(t):Time-distributed UHx(t):Computed time

10、 distribution of rainfally(t):Time distribution of direct runoffApril 30,2009Principle of Hydrology,BNU15Discrete Form of Convolution Process April 30,2009Principle of Hydrology,BNU16Steps to Develop UH1.Analyze the streamflow hydrograph to permit separation of surface runoff from base flow2.Estimat

11、e the total volume of surface runoff(direct runoff)from the storm producing the original hydrograph,the area under the hydrograph after base flow is removedApril 30,2009Principle of Hydrology,BNU17Steps to Develop UH3.Divide the ordinates of the direct runoff hydrograph by total direct runoff volume

12、,and plot these results versus time as a unit graph4.Calculate the effective duration of runoff-producing rain for this unit graph from the hyetograph of the storm event used.April 30,2009Principle of Hydrology,BNU18S-HydrographApril 30,2009Principle of Hydrology,BNU19S-Hydrograph ApplicationApril 3

13、0,2009Principle of Hydrology,BNU20Instantaneous Unit Hydrograph(IUH)Another definitionThe hydrograph of runoff that would result if 1 in.of water were spread uniformly over an area in an instant and then allowed to run off.April 30,2009Principle of Hydrology,BNU21Synthetic Unit HydrographGamma distr

14、ibutionApril 30,2009Principle of Hydrology,BNU22Hydrograph RoutingPurposesPredict the temporal and spatial variations of a hydrograph as it traverses a river reach or reservoirClassification(physical process equation of motion)Hydrologic approachHydraulic approachApril 30,2009Principle of Hydrology,BNU23SummariesUnit HydrographUH derivationUH applicationApril 30,2009Principle of Hydrology,BNU24April 30,2009Principle of Hydrology,BNU25