A storm event occurred on Falls Creek Watershed that produced a rainfall pattern of 5 cm/hr for the first 10 min, 10 cm/hr in the second 10 min, and 5 cm/hr in the next 10 min. The watershed is divided into three subbasins (see Fig. P4-14), with the unit hydrographs given in the following table. Subbasins A and B had a loss rate of 2.5 cm/hr for the first 10 min and 1.0 cm/hr thereafter. Subbasin C had a loss rate of 1.0 cm/hr for the first 10 min and 0 cm/hr thereafter. Using a simple lag routing method (time shift the hydrograph by K), determine the storm hydrograph at point 2. Assume a lag time K of 30 min.

Ten-Minute Unit Hydrographs

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2 Subbasin A Subbasin B Subbasin C Time 2 Time Time (min(m(m/s) (minms) m /s 10 20 30 40 50 60 16.7 33.4 50.0 40 33.4 16.7 10 20 30 10 10 15 20 25 10 30 20 60 70 80 20 15 10 60 15 90 100 100