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A broad, shallow, gently sloped channel for conveying stormwater runoff. It may be lined with vegetation, compost, riprap, or other material and is designed to slow runoff velocity, trap particulates, and promote infiltration. Vegetated swales are often referred to as bioswales, enhanced swales, or water quality swales.

  • Dry swale (bioswale)—incorporates additional elements in the design. Water treatment is aided by a soil bed (natural or amended) with an underdrain system typically composed of a perforated pipe surrounded by gravel.
  • Wet swale—temporarily retains stormwater runoff, but unlike the dry swale, lacks an underdrain system. The wet swale is marsh-like and supports wetland vegetation that is adaptable to variable moisture conditions.