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(A) Event hydrograph routing methods shall be used to calculate design runoff volumes for site runoff facilities. The methods must be HEC-1, (SCS methodology), HEC-HMS, TR-20, or TR-55 tabular method. For sites of 40 acres or more the methods used must be acceptable to FEMA. Event methods shall incorporate the following assumptions:
(1) Antecedent moisture condition = 2;
(2) Appropriate Huff rainfall distribution; and
(3) 24-hour duration storm with a 1% probability (100-year frequency) of occurrence in any one year as specified by Illinois State Water Survey Bulletin 70 Northeast Sectional rainfall statistics.
(Ord. 06-0383, passed 3-15-06)