2008 005 Ordinance - Laserfiche WebLink

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(2) The perimeter of all permanent pool areas deeper than 4 feet shall be surrounded by an aquatic bench that extends at least 8 feet and no more than 15 feet outward from the normal water edge. The 8 feet wide portion of the aquatic bench closest to the shoreline shall have an average depth of 6 inches below the permanent pool to promote the growth of aquatic vegetation. The remainder of the aquatic bench shall be no more than 15 inches below the permanent pool to minimize drowning risk to individuals who accidentally or intentionally enter the basin, and to limit growth of dense vegetation in a manner that allows waves and mosquito predators to pass through the vegetation. The maximum slope of the aquatic bench shall be 10 (H) to 1 (V). The aquatic bench shall be planted with hearty plants comparable to wetland vegetation that are able to withstand prolonged inundation. (3) A forebay designed to allow larger sediment particles to settle shall be placed at basin inlets. The forebay volume shall be equal to at least 10% of the water quality volume (WQv). Alterative post-construction BMPs: The applicant may request approval from the Mayfield Village Engineer for the use of alternative structural post-construction BMPs if the applicant shows, to the satisfaction of the Mayfield Village Engineer and with prior written approval from Ohio EPA, that these BMPs are equivalent in pollutant removal and runoff flow/volume reduction effectiveness to those listed in Table 2. D. Storm Water Quantity Control: The Comprehensive Storm Water Management Plan shall describe how the proposed storm water management practices are designed to meet the following requirements for storm water quantity control for each watershed in the development: The peak discharge rate of runoff from the Critical Storm and all more frequent storms occurring under post-development conditions shall not exceed the peak discharge rate of runoff from a 1-year, 24-hour storm occurring on the same development drainage area under pre-development conditions. Storms of less frequent occurrence (longer return periods) than the Critical Storm, up to the 100-year, 24-hour storm shall have peak runoff discharge rates no greater than the peak runoff rates from equivalent size storms under pre-development conditions. The 1, 2, 5, 10, 25, 50, and 100-year storms shall be considered in designing a facility to meet this requirement. The Critical Storm for each specific development drainage area shall be determined as follows: a. Determine, using a curve number-based hydrologic method that generates hydrographs, or other hydrologic method approved by the Mayfield Village Engineer, the total volume (acre-feet) of runoff from a 1-year, 24-hour storm occurring on the development drainage area before and after development. These calculations shall meet the following standards: (1) Calculations shall include the lot coverage assumptions used for full build out as proposed.