The Critical Storm for a specific development area shall be determined as follows:
(a) The total volume of storm water runoff from a one year frequency 24 hour storm occurring on the development area before and after development shall be determined. The total runoff volume shall be determined by a "Peak Discharge Method" of calculation peak rate and total volume of runoff as described in the U.S. Soil Conservation Service's "Urban Hydrology for Small Watersheds,” Technical Release No. 55 and its latest editions, including all applicable supplements or other accepted methods as approved by the Village Engineer. This hydrologic method shall also be utilized for all detention basin inflow design calculations.
(b) Based upon the volumes calculated in subsection (a) hereof, determine the percent increase in volume of runoff due to the development and using this percentage, select the 24 hour Critical Storm from the following table.
If the percentage of increase in volume of runoff is: | ||
Equal to or greater than | Add less than | The Critical Storm for discharge limitation will be |
-- | 10 | 1 Year |
10 | 20 | 2 Year |
20 | 50 | 5 Year |
50 | 100 | 10 Year |
100 | 250 | 25 Year |
250 | 500 | 50 Year |
500 | -- | 100 Year |
(Ord. 1990-13. Passed 2-12-90.)