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The following problem involves determining the size (storage volume) needed for a stormwater detention basin to reduce the peak discharge (outflow) after development to be no greater than the peak discharge observed before development in a 260 acre watershed. The process for doing so can be broken into three main tasks: (a.) Develop 20-min unit hydrographs using the triangular form of the NRCS synthetic hydrograph for the before and after development conditions assuming the time of concentration changes from 150 minutes before development to 83.6 minutes after development. Use a computational time step of 20 minutes to compute ordinates of each unit hydrograph. Provide your table of ordinates and a plot of each unit hydrograph, as well as any necessary calculations. (b.) Apply the lagging procedure to compute the runoff hydrographs corresponding to before and after development conditions which would occur in response to a storm yielding the depths of rainfall excess (i.e. AVR) tabulated below. Provide tables showing your application of the lagging procedure, the ordinates of the resulting runoff hydrographs, and plots of the hydrographs. Time (min) 0 AVR Before Development (inches) 0.0 AVR After Development (inches) 0.0 0.6 20 0.3 40 0.5 1.0 60 1.0 1.6 80 0.8 1.2 100 120 0.5 0.2 0.8 0.4 (c.) Compute the needed storage (ft?) for a detention basin to yield a peak discharge after development equal to the peak discharge before development. The following problem involves determining the size (storage volume) needed for a stormwater detention basin to reduce the peak discharge (outflow) after development to be no greater than the peak discharge observed before development in a 260 acre watershed. The process for doing so can be broken into three main tasks: (a.) Develop 20-min unit hydrographs using the triangular form of the NRCS synthetic hydrograph for the before and after development conditions assuming the time of concentration changes from 150 minutes before development to 83.6 minutes after development. Use a computational time step of 20 minutes to compute ordinates of each unit hydrograph. Provide your table of ordinates and a plot of each unit hydrograph, as well as any necessary calculations. (b.) Apply the lagging procedure to compute the runoff hydrographs corresponding to before and after development conditions which would occur in response to a storm yielding the depths of rainfall excess (i.e. AVR) tabulated below. Provide tables showing your application of the lagging procedure, the ordinates of the resulting runoff hydrographs, and plots of the hydrographs. Time (min) 0 AVR Before Development (inches) 0.0 AVR After Development (inches) 0.0 0.6 20 0.3 40 0.5 1.0 60 1.0 1.6 80 0.8 1.2 100 120 0.5 0.2 0.8 0.4 (c.) Compute the needed storage (ft?) for a detention basin to yield a peak discharge after development equal to the peak discharge before development