Question

1. A section of a downtown business area 35,400 ftdrains to a single stormwater inlet. The runoff coefficient for this drainage area has been estimated to be 0.72. Based of a specified design return and the time period of concentration of the drainage area, the design storm intensity has been determined to be 4.4 in/hr. Determine the peak runoff rate in cfs from this area to be used for the design of the storm water inlet. 2. Determine the drain size, the horizontal drainage pipe and the leader drainage pipe size for a 15,000 ft' roof area (1/4" slope per 12" of pipe) designed to have two drains on a building located in Houston, TX.

Answer 1

Solution 1 :- q = CiA

where C is a runoff coefficient

i is the rainfall intensity

A is the subcatchment area.

Area A, must be in acres for use in the Rational Method equation, a useful conversion factor is 43,560 ft²/acre is used.

  = (0.72)(4.4)(35400/43560) cfs

= 2.57 cfs