Question

Consider a catchment that has a total area of 2.1 acres. Runoff from the entire catchment flows into one pipe inlet. Part of the catchment is a softball field (1.5 ac) and the other part is a set of paved tennis courts (0.6 ac). The softball field has a C value of 0.3 and a time of concentration of 7 minutes, and the paved area has a C value of 0.95 and a time of concentration of 2 minutes.

The IDF curve is given by i =100/(t_c+ 10) where i is in in/hr and t_c is in minutes. Determine the design storm intensity and flowrate for the following cases:

(a) The usual method based on the entire drainage area contributing to flow.

(b) A modified method that assumes that only the paved tennis courts contribute to flow.

(c) A different modified method that assumes a time of concentration of 2 minutes, and an approximation that the entire tennis court region contributes flow and 2/7 of the softball region contributes flow. Comment on the results and their impact on design. Is it always best to use method (a)? When would method (b) or (c) be better?

Answer 1