I am reviewing some calculations for peak discharge using the rational method from a 4 acre area. A statement in the calculations is that due to the steep slope of the drainage area (8.8%), which is not explained, the time of concentration can be neglected. I cannot find any backing for this statement. The calculation goes on to use a value for the rainfall intensity of 6 inches/hour and references the 24 hr/25 year storm event (Madison County, NE). I do not know if this is connected to the first statement or not. We do see this all the time where the rainfall intensity in the rational equation is mistaken for the 24 hr/25 year storm event from the maps incldued in TR-55.
Any suggestions would be great.
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