Bioswales for Stormwater Management

Photo © Aaron Volkening

Do you live in a community with expansive impermeable parking lots or on a street with dirt or grass along the sidewalk? These designs are known for being ineffective at absorbing the runoff from rainstorms. Bioswales may be a viable solution for your area.


Photo © Brenda VR

Bioswales are used as an alternative to storm sewers and are becoming increasingly common in urban areas–alongside roads, sidewalks, and in parking lots. Bioswales (you might have a clearer picture if you think of them as ditches) capture water and allow it to undergo a natural filtration process right there, rather than heading to a storm sewer.

Puddle Reflection

Photo © Lois Elling

As rain events occur, water “runs-off” impermeable surfaces like rock, asphalt, and concrete. It can either run into an out-of-the-way bioswale and be absorbed by the plants surrounding the impermeable or semipermeable surfaces, or it can find its way into a storm sewer.

Have a Bioswale to Map?

Photo ©

In the toolshed, choose “second” for mapping a habitat. Bioswales are lumped together with rain gardens and bioretention cells–all of which are considered “Stormwater Management”. Once you have mapped this area, you can tell us more about this habitat, like the specific type of feature that it is, the run-off source, the % native plants used, and the run-off source size.

Photo ©

Native grasses, shrubs, and flowers are often used for bioswale projects. Native plants often require less maintenance, provide habitat for local wildlife, and are excellent at controlling erosion during large rain events. Native plants are also adapted to the growing conditions of the region where the bioswale is installed, so they are more tolerant of local weather events.

Sidewalk Bioswale

Photo © Dianne Yee

Bioswales are recommended to be a parabolic or trapezoidal shape with slopes no steeper than 3:1 (3 feet horizontal to 1 foot vertical). The required size of the bioswale depends on the area it is being installed. The swale should be capable of handling the quantity of runoff in the designated area, or have an overflow system. This allows for water to effectively move and be absorbed by plants at a rate that can be handled for proper filtration.

Bioswale in construction

Photo © Darien Library

Coaxing new development into including bioswales is a great way to increase the sustainability of new buildings, and to reduce the drag of development on aging infrastructures. They are fantastic updates to existing neighborhoods without proper drainage as well, since they can be built without tapping into city infrastructure.

Curb Bioswale

Photo © Steven Vance

With some foresight, they can be built around existing infrastructure, providing relief to frequently backed-up storm sewers. The swale above likely replaces an area that use to have a persistent puddle.

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