An extreme rainstorm has occurred at the Dry Creek watershed. The intensity of r

Question

An extreme rainstorm has occurred at the Dry Creek watershed. The intensity of rainfall excess (k) is shown below. Also shown is the i-hour unit hydrograph for Dry Creek. Assume the baseflow in the creek at the time of the storm is a constant 15 cfs. The area under the direct runoff hydrograph is given as 2 x 10 cubic ft. Time (hr) 1-hr UH (cfs) 0 80 120 60 20 4 Time (hr) ie (in/hr) 0-2 2-4 1.0 Use this information to determine the following. (a) The watershed area in mi-. (b) The direct runoff hydrograph (in cfs) in tabular form. Please do not draw the hydrograph. (e) The peak discharge of the streamflow hydrograph.

Explanation / Answer

Effectife rainfall in 0-2 hrs=2inch=1/6ft

Effectife rainfall in 2-4 hrs=3inch=1/4ft

Total Effectife rainfall =5/12ft

Area of watershed = A=(area under drh)/(total effective rainfall)

A=4.8*107 ft2 = 1.7218 mi2    Answer(a)

3

Hence, Peak streamflow discharge hydrograph = 46.667ft/s

*hope you like the solution*

Time(hr) UH of 1hr(cfs) S Curve addition S Curve offset S curve Y DRH due to 1/6ft rain in 2hr(cfs) DRH due to 1/4ft rain in 2hr(cfs) Resulting DRH(cfs) Base flow in(cfs) streamflow hydrograph(cfs) 0 0 0 - 0 0 0 0 15 15 1 80 0 80 - 80 6,67 0 6.67 15 21.67 2 120 80 200 0 200 16.67 0 16.67 15 31.67

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60 200 260 80 180 15 10 25 15 40 4 20 260 280 200 80 6.67 25 31.67 15 46.67 5 0 280 280 260 20 1.67 22.5 24.17 15 39.17 6 - - 280 280 0 0 10 10 15 25 7 - - - 280 0 0 2.5 2.5 15 17.5 8 - - - 280 0 0 0 0 0

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