Stormwater Quality Design Manual (May 2007) - City of Sacramento ...

Runoff Treatment Control Measure Fact SheetWater Quality Detention Basins• Maximize residence time by placing the inlet and outlet on opposite ends of the basin. Ensuringthe length is at least three times the width, as measured down the center of the flow path. Forpermanent ponds, incorporate additional features to maximize residence time, such as:• Contouring the basin bottom to baffle flows and promote mixing.• Using islands or peninsulas.• If possible, designing the deepest point to be at least 8 ft. deep.• Incorporate access. See step 5.• Incorporate a concrete low flow channel in dry basins (see Figures DB-4 and DB-5).• Consider an aquatic bench with emergent vegetation around the perimeter of wet ponds andpermanent pools to help with water quality and to provide a safety feature.See Figure DB-4 for an example of a dry extended detention basin.Figure DB-3. Basin Criteria to Control Stormwater PollutionDry-Extended Detention BasinStorm discharge: release 75% of WQV in aminimum of 24 hours, 100% of WQV within48 hours total.Dry weather treatment: vegetated gravel bedor other approved feature.WQV*Wet BasinStorm discharge: based on the downstreamdrainage systems capacityDry weather treatment included in permanentpoolWQV*Combination BasinStorm discharge: release 75% of the 0.5WQV in a minimum of 24 hours, 100% of the0.5 WQV within 48 hours total.Dry weather treatment included in permanentpoolWQV**WQV is the Water Quality Volume per Appendix EStormwater Quality Design Manual for the Sacramento and South Placer RegionsMay 2007DB-5