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

Runoff Treatment Control Measure Fact SheetStormwater PlanterDesign CriteriaDesign criteria for stormwater planters are listed in Table SP-1. A Design Data Summary Sheet (TableSP-3) is provided at the end of this fact sheet.Table SP-1. Stormwater Planter Design CriteriaDesign Parameter Criteria NotesTributary drainagearea≤ 1 acreIdeally suited for small areas such as parking lot islands, perimeter buildingplanters, street medians, roadside swale features, and site entrance orbuffer features. Can be implemented on a larger scale, provided the WQVand average depth requirements are met.Design volume WQV See Appendix E in this Design ManualDesign drawdown time 12 hrs Period of time over which WQV drains from planter.Design averagesurcharge depth (d s )Containment curb(if applicable)Inlet curb cuts(if applicable)Topsoil layerSand-peat layer6-12 in.height >6 in.≥ 12 in.wide6 in.(minimum)18 in.(minimum)Design to deter skateboarding and satisfy ADA requirementsGravel layer 9 in. ASSHTO #8 Coarse AggregateFilter fabricMinimum widthUnderdrain(as required)30 in.3-4-inchperforatedpipeTo prevent clogging and promote flow spreading. Pavement should beslightly higher than swale. Include energy dissipaters.Sandy loam topsoil. Deeper layer recommended for better vegetationestablishmentDesign mix to achieve approx. 3-4 inches/hr infiltration rate and provide 12hour drawdown; check with permitting agency for verification.Between sand/peat and gravel layersFor all flow-through planters, planters within 10 ft. of a building foundation,and infiltration planters where underlying soils have lower permeability thanthe planter’s sand/peat media layerOverflow device Varies Connect to storm drain system. See Figures SP-1 and SP-2 forrecommended designs. Alternative designs may be allowed; check withpermitting agency.WaterproofingmembraneRequired for planters adjacent to building foundations.Design ProcedureStep 1 – Calculate Water Quality Volume (WQV)Using the calculations given in Appendix E, determine the contributing area and stormwater qualitydesign volume, WQV, based on a 12-hour drawdown period.Step 2 – Design average surcharge depth (d s )Select the average WQV depth between six (6) and twelve (12) inches. Average depth is defined as watervolume divided by the water surface area of the planter.Stormwater Quality Design Manual for the Sacramento and South Placer RegionsMay 2007SP-3