1). As part of your contract with the City of Denver, you must estimate peak run
ID: 117601 • Letter: 1
Question
1). As part of your contract with the City of Denver, you must estimate peak runoff flow from precipitation on the Bronco's new football stadium a) Select a runoff coefficient (table 11.3, pg. 408) b) Calculate peak discharge (Q CIA) c) What is the maximum runoff if they tarp the whole field? You have the following information: Area of field = 1 1,250 yards* 2.3 acres Maximum probable precipitation -0.5 inch/hour for 48 hours All of the runoff discharges at one point A separate drainage system has been designed for the stands Qp = CIA where 2p- the peak runoff rate (cfs) C = the runoff coefficient (assumed to be dimensionless) I-the average rainfall intensity (in/hr) for a storm with a duration equal to a critical period of time tc = the time of concentration (see Chapter 9) A = the size of the drainage area (acres) CI the average net rain intensity (in/hr) for a storm with duration =Explanation / Answer
Rational Equation: Q=CIA
The Rational equation requires the following units:
Q = Peak discharge, cfs
C = Rational method runoff coefficient
I = Rainfall intensity = 0.5 inch/hour
A = Drainage area = 2.3 acre
a) The Rational method runoff coefficient, C can be taken as 0.20, the least among the playgrounds and maximum among the lawn as a football field is typically a grassed playground.
b) Therefore, Q = 0.2*0.5*2.3 = 0.23 cfs
c) If the whole field is tarped the Rational method runoff coefficient, C goes up to a maximum of 0.95-0.98 as there will still be some leakages here and there.
Considering C=0.98,
Q = 0.98*0.5*2.3 = 1.127 cfs
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