2006-016 Ordinance - Laserfiche WebLink

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,., Ordinance No. 2006-16 (1) Through a site hydrologic study approved by the local municipal permitting authority that uses continuous hydrologic simulation and local long-term hourly precipitation records or (2) Using the following equation: (A) WQ~ = C * P * A / 12 where: WQ~ =water quality volume in acre- feet C =runoff coefficient appropriate for storms less than 1 inch (see Table 1) P = 0.75 inch precipitation depth A =area draining into the BMP in acres Table 1 Runoff Coefficients Based on the Type of Land Use Land Use Runoff Coefficient Industrial & Commercial 0.8 High Density Residential (>8 dwellings/acre) 0.5 Medium Density Residential (4 to 8 dwellings/acre) 0.4 Low Density Residential (<4 dwellings/acre) 0.3 Open Space and Recreational Areas 0.2 (d) Where the land use will be mixed, the runoff coefficient should be calculated using a weighted average. For example, if 60% of the contributing drainage area to the storm water treatment structure is Low Density Residential, 30% is High Density Residential, and 10% is Open Space, the runoff coefficient is calculated as follows (0.6)(0.3) +(0.3)(0.5) +(0.1)(0.2) -- 0.35. (e) An additional volume equal to 20 percent of the WQ~ shall be incorporated into the BMP for sediment storage and/or reduced infiltration capacity. The BMPs will be designed according to the methodology included in the Ohio Rainwater and Land Development manual, ODOT Post-Construction storm water standards, or other manual that is acceptable to Ohio EPA. (f) BMPs shall be designed such that the drain time is long enough to provide treatment, but short enough to provide storage available for successive rainfall events as described in Table 2 below Table 2: Target Draw Down (Drain) Times for Structural Post-Construction Treatment Control Practices Best Management Practice Drain Time of WQv Infiltration 24 - 48 hours Vegetated Swale and Filter Strip 24 hours Extended Detention Basin (Dry Basins) 48 hours 12