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<br />Basic steps in a Regional Study Using the Lhit Hydrograph Procedures of <br />HEC-l: <br /> <br />1. Collect precipitation and runoff information for B range of major <br />flood events in the region. Identify the watershed and subbasin boundaries <br />Dn a topographic map. Index points where discharge-frequency estimates are <br />desired should be located. The subbasins are chosen to include these index <br />points, desired hydrological components, and stream gage locations. Basins <br />adjacent are also used if they are hydrologically and meteorologically <br />similar. <br /> <br />2. Perform an HEC-l rainfall-runoff analysis to optimize the unit <br />hydrograph and loss-rate parameters for the gaged drainage areBS. <br /> <br />3. Correlate the unit hydrograph and loss-rate parameters with basin <br />characteristics and develop generalized relationships for these parameters. <br /> <br />4, Divide region into subbasins correspDnding to their hydrologic <br />characteristics and to the index points at which discharge-frequency <br />estimates are needed, and also to capture the spatial variations in <br />precipitBtion. <br /> <br />5, The generalized relationships developed in Step 3 are used to <br />compute parameters for the ungaged subbasins using measurable subbasin <br />characteristics. <br /> <br />6. A watershed sirulation using HEC-l is next performed for several <br />histDrical storm events. If the reconstituted runoff peaks and volumes at <br />downstream gages are silJ1ificantly different from observed hydrographs, the <br />unit hydrograph, loss-rate, and/or routing parameters rust be adjusted and <br />the analysis repeated. <br /> <br />2.3 Continuous SirulBtion with Historical'Precipitation'Data <br /> <br />An alternative method to the single event modeling approBch is <br />continuous sirulation with long term precipitation data after calibrating the <br />model with several years of continuous data. This approach could be used <br /> <br />8 <br /> <br />e <br /> <br />e <br /> <br />e <br />