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

Technical RequirementsVegetated SwaleDescriptionA vegetated swale is a wide, shallow, open channelplanted with dense, sod-forming vegetation anddesigned to accept runoff from adjacent surfaces.As the runoff slows and travels through thevegetation and over the soil surface, pollutants areremoved by a variety of physical and chemicalmechanisms, including sedimentation, filtration,adsorption, precipitation, and microbial degradationand conversion.Siting Considerations• Drainage area: 10 acres maximum per swale.• Longitudinal Bottom Slope: 0.5%-2.5%• Underdrains required for slopes less than 1%. For slopes up to5%, check dams can be used to reduce slopes to 2.5%.• Minimum Bottom width: 2 ft.• Side slopes: 3:1 or flatter.• Liners may be required in areas where swales may be impactedby hazardous materials or where spills may occur (e.g., retailgasoline outlets, auto maintenance businesses,processing/manufacturing areas).• Surface flow into swale preferred instead of undergroundconveyance.Vector Considerations• Potential for mosquitoes due to standing water will be greatly.reduced or eliminated if the swale is properly designed, constructed, and maintained.Advantages• Relatively inexpensive when used to replace part of a conventional storm drainage system andintegrated into site landscaping.• Provides both stormwater treatment and conveyance.• Reduces peak flows during small storm events.• Attractive and easy to maintain.Limitations• May conflict with water conservation ordinances related to landscape irrigation needs.• May not be appropriate for industrial sites or locations where spills may occur unless liner is usedto prevent infiltration.General Maintenance Recommendations (Low to Moderate)• Periodically remove debris and sediment from inlets and swale.• Repair/replace vegetation as necessary to maintain full cover and prevent erosion.• See table VS-2 for additional vegetation maintenance recommendation.POLLUTANT REMOVALEFFECTIVENESSSedimentNutrientsTrashMetals*Bacteria*Oil and GreaseOrganics*MediumLowLowMediumLowMediumMedium*The following are target pollutants forSacramento area: copper; lead; mercury;pathogens; diazinon; and chlorpyrifosSource: CASQA California StormwaterBMP Handbook, January 2003Stormwater Quality Design Manual for the Sacramento and South Placer RegionsMay 2007VS-1