Hamilton County Soil and Water Conservation District

EARTHWORK ADMINISTRATION

Detention Basins

Detention Basins retrofitted with a slow release device are one of the best management practices in containing sediment at the construction site. They are almost always strategically located at the lowest elevation on the site where runoff flows to and a majority of times serve as the last line of defense before sediment laden runoff leaves the site. The slow release device is usually a perforated riser pipe wrapped with geotextile and retrofitted into the release structure of the basin. The slow release device allows ponding of the runoff before it is released into receiving streams and waterways. The ponding has a twofold effect. It allows for detention and settling time for the soil particles and also slows down the flow of the runoff and deflects the energy which causes sediment also to settle at the runoff and ponded water interface. It is also proven that installing baffles along the runoff path in front of the slow release device improves the basin’s efficiency in trapping the sediment and makes maintenance of the basin easier. To be effective, detention basins equipped with slow release devices should be installed first before any substantial clearing or at least at the earliest possible time during the construction project. As part of a good maintenance schedule, a basin should be mucked out if the accumulated silt reaches 40 % of the basin capacity. This would make better efficiency of the basin and also restore its capacity.

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