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

Runoff Treatment Control Measure Fact SheetStormwater PlanterHow does a Stormwater Planter work?A stormwater planter is designed to receive runoff from downspouts, piped inlets or sheet flow fromadjoining paved areas. A shallow surcharge zone above the vegetated surface temporarily stores runoff(the water quality volume or WQV). The runoff gradually infiltrates through the root zone of thevegetation and into the underlying sand/peat bed where it fills the pore spaces. A variety of naturalmechanisms remove pollutants from the runoff as it infiltrates through the root zone and is detained in thesand/peat bed before reaching a base layer of gravel.If infiltration to the underlying soil is not possible or desired, a flow-through stormwater planter with animpermeable bottom liner and underdrain should be used. The underdrain gradually dewaters thesand/peat bed over the drawdown period and discharges the runoff to the downstream storm drain system.If an infiltration planter is used, there is no impermeable bottom liner, and runoff percolates into theground. An underdrain may still be needed if the permeability of the underlying soils is lower than thesand/peat layer, but at least a portion of the treated runoff will infiltrate into the underlying soil. SeeFigures SP-1 and SP-2 for typical stormwater planter configurations.Other Names: Bioretention, Infiltration Planter, Flow-through Planter, Biofilter, Porous LandscapeDetention, Rain GardenPlanning and Siting Considerations• For infiltration type planters, consult a geotechnicalengineer about site suitability.• Select location where site topography is relatively flatand allows runoff drainage to the stormwater planter.• Integrate stormwater planters into other landscape areaswhen possible.• Stormwater planters may be located within landscapeareas as “rain gardens” and may have a non-rectangularfootprint to fit the site landscape design.• In expansive (C, D) soils, locate stormwater planters farEarly Design IsCritical!Stormwater planters must belocated on the site plan at theearliest possible designphase when laying out thebuilding and parkingfootprints and before the sitegrading plan is prepared.enough from structures to avoid damage to foundations (as determined by a structural orgeotechnical engineer). 10 feet is given as a rule-of-thumb on the first page of this fact sheet.Alternatively, use a flow-through stormwater planter.Parking lot rain garden, Kansas City, MOResidential rain garden, MinnesotaStormwater Quality Design Manual for the Sacramento and South Placer RegionsSP-2 May 2007