A 20 ha development site is wooded and has a permeability rate of 35 mm/h. The development creates 5 acres of pavement and turns another 5 acres into lawn, all hydraulically connected. The time of concentration is calculated at 30 minutes and 20 minutes for the pre- and postdevelopment conditions, respectively. Using the universal runoff model, developed by the author, estimate the required detention storage to produce 50% and 20% reductions in the peak rates of runoff for the 2- and 100-year frequency storms, respectively. The local IDF curves show the following rainfall intensities:

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Storm Frequency (years) Storm Duration Rainfall Intensity (mm/h) 2 20 50 30 40 100 20 120 30 80