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Vegetated Swales

Vegetated Swales

Vegetated Swales

Description: Vegetated swales are shallow open channels lined with dense vegetation designed to treat, attenuate, and convey excess runoff. Vegetated swales can replace curb or gutter systems and al- though they require more space, they manage runoff better.

Purpose: As the runoff flows along the length of the swale, the vegetation slows and filters the water allowing it to infiltrate into the ground. Where soils do not drain well, swales are typically lined and con- vey runoff to a drywell or infiltration trench. A swale can look like a typical land- scaped area. Vegetated swales can be designed to provide infiltration, but are primarily used to convey water.

How to:

The recommended slope for vegetative swales is 1-4%. For steeper slopes (up to 5%), check dams are recommended to reduce flow velocity and erosion potential. In areas of steep slopes, swales should run parallel to contours of the landscape. Swales may not be appropriate for highly sloped areas.

Grasses or sedges are typically used in vegetated swales, but other native plants can be used as well. Please refer to the Planting and Maintaining Vegetation Areas BMP for a list of recommended native species.

The bottom of a swale should be 2-4 feet above the seasonal high water table.
Outlet protection should be provided at the swale’s discharge point to pre- vent scour or erosion.