Question

A 23-acre watershed undergoes development. The runoff coefficients (C) for pre-­development and post-development conditions are 0.2 and 0.4, respectively. The ­pre-­development and post-development times of concentration are 0.25 and 0.15 hour, respectively. Estimate the depth (in.) and volume (acre-ft) of detention storage required using the loss-of-natural-storage method. Assume that the IDF curve shown in Figure 2.4 applies and that the design policy requires control for a 10-year event. (Use Triangular Hydrograph Method)

Baltimore, Maryland 1903-1951 20.0 15.0 Note Frequency analvsis by method of extreme value after gumbel 10.0 8.0 6.0 Return period (years) 4.0 25 10 2.0 0.8 0.6 0.2 0.08 0.06 0.04 0.02 10 15 20 30 40 5060 2 3 4 5 6 8 1012 18 24 Hours Minutes Duration Figure 2.4 Rainfall intensity-duration-frequency (National Weather Service, 1961)

Answer 1

An sven cata rea lacre edeve monl ConditiO intensey.ufn /hr Assuni A3 acre -01 A.

h60min A 3 31 6 23 "오 21 16-Q 0 0i65 x 16.2

agao-03 A Q3 unoff 2 O IS X60 5 38. 2 3

386 n (umi O man 0.386, O-2여 12 12