(A) In order to minimize runoff damage to downstream properties, sediment pollution of public and private waters, and hydraulic overloading of existing drainage facilities, the storm water runoff from a site after development shall not exceed the discharge from that site generated by single-family development (at a density of 3.5 units per acre). The amount of water to be retained shall be determined by the method described in the following divisions:
(1) Pre-development (equivalent to a single family at 3.5 units per acre). Calculate the site runoff based on a 25-year storm frequency and existing ground conditions using a coefficient of runoff based on C = 0.50.
(2) Post-development runoff. Calculate the proposed ultimate development runoff based on a 50-year frequency curve. Use a weighted coefficient of runoff based on the proposed development with C = 0.95 for impervious areas and C = 0.40 for unpaved and grass areas.
(3) Storage requirement. Provide on-site retention of storm water equal to the post-development runoff rate minus the single family runoff rate for a period of 30 minutes.
(4) Discharge from retention basin.
The discharge from the retention basin shall be equal to the computed single family runoff minus any flow discharging directly from the development site.
(B) Retention basins: standards and specifications. These standards apply to permanent and temporary storm water runoff, sediment, and debris basins formed by an embankment or excavation. These standards are limited to the installation of basins on sites where:
(1) Failure of the structure will not result in loss of life, damage to homes, or interruption of use or service of public utilities.
(2) The drainage area does not exceed 200 acres.
(3) The water surface at the crest of the emergency spillway does not exceed five acres.
(C) General notes.
(1) All computations are to be prepared by an engineer licensed in the Commonwealth of Kentucky and submitted to the Public Works Department for review.
(2) All detention areas and methods are to be approved by the Public Works Department.
(3) All detention ponds are to be fenced.
(Ord. O-28-84, passed 10-9-84)