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(A) The storage capacity and discharge rate shall be based upon the calculated volume and peak flow of the storm water runoff, respectively. The calculations for sites having an area of 100 acres or less shall be made using either the Illinois Manual for Soil Erosion and Sedimentation Control Method or the rational method. If the site is larger than 100 acres then the Engineer shall use the Illinois Manual for Soil Erosion and Sedimentation Control Method or if another method is desired to be used, the Engineer shall submit a proposed method of evaluation for the calculations for review and approval. The permitted discharge rate of storm water runoff shall be determined by calculating the rate of runoff for the site’s pre-and post-development conditions.
(B) The Engineer shall determine the most critical storm looking at three different time periods:
(1) The time of concentration;
(2) A one-hour storm; and
(3) A 24-hour storm.
(1999 Code, § 34-5-54)