Vegetated Swale

Also Known As: Grassed Swale, Vegetated Swale (Lined)



Vegetated swales are shallow, open channels that are designed remove pollutants such as sediment by physically straining and filtering water through vegetation within the channel. As stormwater runoff flows along these channels, it is treated through vegetation slowing the water to allow sedimentation, filtering through a subsoil matrix, and/or infiltration into the underlying soils. Additionally, swales can serve as conveyance for storm water and can be used in place of traditional curbs and gutters; however, when compared to traditional conveyance systems the primary objective of a vegetated swale is filtration and water quality enhancement rather than conveyance. Some designs also include infiltration through subsurface soil media, or underlying soils to reduce peak runoff volume during storms.

Vegetated swales are effective for removing

  • Total suspended solids and sediment
  • Oil and grease
  • Organics
  • Metals
  • Organics


Siting and Design:

Drainage AreaSoil Infiltration RateWater Table SeparationDepth to bedrockFacility slopeInflow rate
< 2 ac<> 0.5 in/hr if < 0.5 in/hr, install UD)> 2 ft> 10 ft (if > 2 but < 10 ft, install UD)< 4%Mulch: 1 cfs,
Grass: 3 cfs



TaskFrequencyMaintenance Notes
Inlet inspectionTwice annuallyCheck for sediment accumulation and erosion within the swale.
Mowing2–12 times/yearFrequency depends on location and desired aesthetic appeal.
Watering1 time per 2–3 days for first 1–2 months; sporadically after establishmentIf drought conditions exist, watering after the initial year may be required.
Fertilization1 time initiallyOne time spot fertilization for “first year” vegetation.
Remove and replace dead plants1 time/yearWithin first year 10 percent of plants may die. Survival rates increase with time.
Check damsOne prior to the wet season and monthly during the wet seasonCheck for sediment accumulation and erosion around or underneath the dam materials.
Miscellaneous upkeep Tasks include trash collection and spot weeding.



BMPRetrofit ($/sq ft)O&M ($/sq ft/yr)Retrofit with Underdrain ($/sq ft)New Construction ($/sq ft)New Construction with Underdrain ($/sq ft)
Vegetated Swale6.17120.772.418.11
Vegetated Swale (Lined) 124.74 9.66