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

Runoff Treatment Control Measure Fact SheetConstructed Wetland BasinStep 3 – Determine Basin Depths and Surface AreasDistribution of the wetland area is needed to achieve desired biodiversity. Distribute component areas asindicated in Table CWB-2.a. Estimate average depth of permanent pool (D avg ) including all zonesb. Estimate the water surface area of the permanent pool (A pp ) based on actual V ppA pp = V pp / D avgc. Estimate water surface elevation of the permanent pool (WS Elev pp ) based on site elevations.Table CWB-1. Constructed Wetland Basin Design CriteriaDesign Parameter Criteria NotesDesign volume WQV See Standard Calculation Fact SheetMaximum drawdown time for WQV 48 hours Based on WQVMinimum permanent pool volume 75% Percentage of WQVLiner Clay Required in areas with very permeable soils (e.g.,Types A, B)Inlet/outlet erosion control – Provide energy dissipaters to reduce velocity, subjectto the approval of the permitting agencyForebayVolumeAreaDepthLiner5-10%5-10%4 ftPercentage of WQVPercentage of permanent pool surface areaMinimumConcrete, to facilitate maintenanceOpen-water Zonea. Area (including forebay)b. DepthWetland Zonea. Areab. DepthOutlet Zonea. Areab. Depth10-50%4 ft50-70%0.5-1 ft5-10%3 ftPercentage of permanent pool surface areaMinimumPercentage of permanent pool surface area30 to 50% should be 1.0 ft deepPercentage of permanent pool surface areaMinimumSurcharge depth above permanent pool 2 ft MaximumBasin length to width ratio 2:1 Minimum (larger preferred)Basin freeboard 1 ft MinimumWetland zone bottom slope 10% MaximumEmbankment side slope (H:V) 4:13:1Side slopes (H:V) 5:1(or steeper) InsideOutside (without retaining walls)Maintenance access ramp slope (H:V) 10:1 or flatterMaintenance access ramp width 5-20 ft Minimum. Paved with concrete or porous pavement,subject to approval of permitting agencyStormwater Quality Design Manual for the Sacramento and South Placer RegionsMay 2007CWB-3