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

Runoff Treatment Control Measure Fact SheetConstructed Wetland BasinDescriptionWest David Pond. Photo: Larry Walker AssociatesA constructed wetland basin is an earthen basintreatment system with a permanent pool of waterthat includes four zones: a forebay, an open-waterzone, a wetland zone with aquatic plants, and anoutlet zone. The basin contains an area above thepermanent pool to retain runoff from thestormwater quality design storm (water qualityvolume or WQV) and slowly release excess waterover a specified drawdown period. Constructedwetland basins provide a significant naturalamenity to a community. The basin pictured islocated near Village Homes in Davis.Siting Considerations• Tributary Drainage Area: Up to 100 acres.• Soil Type: Most appropriate for Type C and D soils. For TypeA and B soils, use an impermeable (e.g., clay) liner.• Topography: Not appropriate on fill or steep slopes.Vector Considerations• Potential for mosquitoes exists due to permanent water pool.However, proper design of permanent pool zones, routinevegetation management, and introduction of mosquito fish willminimize the risk.Advantages• Reduces stormwater discharge to surface waters during moststorm events.• Reduces peak flows during small storm events.• Can provide wildlife habitat, high aesthetic value and passiverecreational opportunities.POLLUTANT REMOVALEFFECTIVENESSSedimentNutrientsTrashMetals*Bacteria*Oil and GreaseOrganics*HighMediumHighHighHighHighHigh*The following are target pollutants forSacramento area: copper; lead; mercury;pathogens; diazinon; and chlorpyrifosSource: CASQA California StormwaterBMP Handbook, January 2003Limitations• Supplemental water supply or perennial base flow is required to maintain the permanent pool.• Public safety related to access must be considered; security fencing is generally required by mostpermitting agencies in urban settings.• Will typically require five years to establish.General Maintenance Recommendations (Moderate to High)• Inspect basin annually in early spring.• Periodically remove debris from inlet and outlet structures, and wetland basin itself.• Regularly harvest vegetation and stock with mosquito fish for mosquito control.• Remove accumulated sediment from forebay and other water zones as needed.• Inspect seasonally for abnormal algae growth and address as needed.Stormwater Quality Design Manual for the Sacramento and South Placer RegionsMay 2007CWB-1