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

Runoff Treatment Control Measure Fact SheetVegetated Filter StripDesign ProcedureStep 1 – Calculate Water Quality Flow (WQF) (Flow-BasedControl Measure)Using the Appendix E in this Design Manual, determine thecontributing area and water quality design flow, WQF.Step 2 – Calculate minimum width of Vegetated Filter Strip(W VFS )The design minimum width of the Vegetated Filter Strip (W VFS )normal to flow direction is a determined from the design WQF andthe minimum application rate (q a ), as follows:W VFS = (WQF)/(q a )Early Design IsCritical!Vegetated Filter Stripsmust be located on thesite plan at the earliestpossible design phasewhen laying out thebuilding and parkingfootprints and before thesite grading plan isprepared.W VFS = (WQF)/0.005 cfs/ft (minimum)Step 3 – Determine the minimum length of Vegetated Filter Strip in the flow directionThe length of the filter strip in the flow direction must be a minimum of 25 feet. Greater lengths aredesirable, as somewhat better treatment performance can typically be expected.Step 4 – Determine design slopeSlope of the filter strip surface in the direction of flow should be between one (1) percent and four (4)percent to avoid ponding and channeling of flow. Terracing may be used to maintain a slope of four (4)percent in steeper terrain.Step 5 – Design inlet flow distributionIncorporate a device such as slotted curbing, modular block porous pavement, or other spreader devices atthe upstream end of the filter strip to evenly distribute flow along the top width. Concentrated flowdelivered to the filter strip must be distributed evenly by means of a level spreader as shown in FigureVFS-1.Step 6 – Select vegetationA full, dense cover of sod-forming vegetation is necessary for thefilter strip to provide adequate treatment.Select vegetation that:• Will be dense and strong enough to stay upright, even inflowing water;• Has minimum need for fertilizers;• Is not prone to pests and is consistent with IPM practices;• Will withstand being inundated for periods of time; and• Is consistent with local water conservation ordinancerequirements.Use the design datasummary sheet (TableVFS-3) provided at theend of this fact sheet torecord design informationfor review by the agencyplan reviewer.Do not use bark or similar buoyant material in the filter strip or around drain inlets or outlets.Step 7 – Design outlet flow collectionProvide a means for outflow collection and conveyance (e.g., grass channel/swale, storm drain, gutter).Stormwater Quality Design Manual for the Sacramento and South Placer RegionsMay 2007VFS-3