Designing swales


Swales are incorporated into sustainable drainage systems for small developments or in rural locations, to provide a limited amount of stormwater or run-off storage. They are typically grassed, or can be vegetated with reeds or other aquatic plants that will absorb or treat contaminated water before discharge to a watercourse.


Lake Superior, a resource from Duluth, Minnesota, offers a swales toolkit that covers this drainage feature in some detail.

A grassed swale is a graded and engineered landscape feature appearing as a linear, shallow, open channel with trapezoidal or parabolic shape. The swale is vegetated with flood tolerant, erosion resistant plants.

The design of grassed swales promotes the conveyance of storm water at a slower, controlled rate and acts as a filter medium removing pollutants and allowing stormwater infiltration.

When properly designed to accommodate a predetermined storm event volume, a grassed swale results in a significant improvement over the traditional drainage ditch in both slowing and cleaning of water.

In swales, stormwater is slowed by strategic placement of check-dams that encourage ponding and these ponds in turn facilitate water quality improvements through infiltration, filtration and sedimentary deposition. Collected stormwater is expected to drain away through the soil within several hours or days.

Google image search also provides lots of useful diagrams and photos of typical swale designs. has several categories that can prodvide a useful source of products when specifying swale designs and other drainage features.
Ground engineering



One Response to “Designing swales”

  1. SUDS resources and publications for designers « External Works Says:

    […] Swales are a graded, engineered feature that appear as a straight, shallow, open channel. They are planted with vegetation that is tolerant to flooding and resistant to erosion. […]

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