Research on Dimensionless Unit Hydrograph and Time of Concentration for Maryland Watersheds
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2021-08-31
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Edition:SPR-B Final Report (Aug 2018–Aug 2021)
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Abstract:Observed data from 100 rainfall-runoff events on 54 watersheds in Maryland and Delaware were used to investigate two watershed characteristics: the dimensionless unit hydrograph (DUH) and time of concentration (Tc). Streamflow hydrograph data were obtained from US Geological Survey gaging stations. Event hyetographs were generated from US Weather Service NEXRAD Radar Stage III data (DPR) using a method developed in this study. The gamma-function form of the Natural Resources Conservation Service unit hydrograph was assumed. For each event, an optimization method was used to determine the time to peak and gamma parameter (related to the Peak Rate Factor, PRF) that give the best-fit direct runoff hydrograph when convolved with the rainfall excess hyetograph. Tc was estimated by differentiation of the unit hydrograph. Efforts to predict PRF and Tc using watershed properties, and to update an existing regression equation, were inconclusive. Future investigations will focus on improving the event baseflow separation and determination of rainfall excess.
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