A hydrograph for a 4,250-acre basin is shown in the accompanying sketch. The given hydrogr...

A hydrograph for a 4,250-acre basin is shown in the accompanying sketch. The given hydrograph actually appeared as a direct runoff hydrograph from the basin, caused by net rain falling at an intensity of 0.20 in./hr for a duration of 5 hr, beginning at t = 0.

(a) Determine the excess release time of the basin.

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(b) What percentage of the drainage basin was contributing to direct runoff 4 hr after rain began (t = 4)?

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(c) Use your response to part (b) to determine Qp, as shown in the sketch. Do not scale Qp from the drawing.

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(d) Note that rain continued to fall between t = 3 and t = 5. Why did the hydrograph form a plateau between t = 3 and t = 5, rather than continue to rise during those 2 hours?