Question

General data for this problem to be used in the rational method approach and the water balance: The 25-yr IDF curve for a 19,955 m2 watershed area is given by the equation I = A/(B+t) where I is the average rainfall intensity in mm/h, t is the rainfall duration in minutes, A = 22,000 and B = 80. Area has composite runoff coefficient C=0.82 and time of concentration tc= 20 min = 0.3333 h. For the special case of the current problem, let time to peak = time of concentration = rainfall duration and let the time base of the rational method triangular hydrograph = 40 min = 0.6667 h. The rational method is used to determine the peak flow rate required to design the stormwater system at the outlet system.

Determine:

a) The 25-yr design rainfall intensity in cm/h for rainfall duration = 20 minutes.

b) The surface runoff peak flow based on the rational method in m3 /s for rainfall duration.

c) Total precipitation depth (cm) from rainfall event.

d) The precipitation volume (m3 ) from rainfall event.

e) The runoff depth (cm) generated from this runoff hydrograph.

f) Then determine the corresponding runoff volume (m3 )

g) Compare the precipitation depth (part c) and volume (m3 ) (part d) with the runoff ones generated in the hydrograph of part (e) and

(f). Explain what you see from these value

Answer 1