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Bioswale Illustration

Type of Development

New Development, Restoration


Hills, Valley


Long Term


Natural Habitat, Urban




Vary greatly depending on size.


Bioswales are long biorientation areas that allow stormwater to slow down and filter through the ground. They are usually large, long, curving areas of depressed land filled with thick rooted native plants and rocks placed near flood zones, and are best used in place of underground pipes and in areas untouched by concrete. Bioswales can be used on a small scale in residential neighborhoods or can cover hundreds of feet along floodplains or highways.

Illustration of urban ecosystem that supports biodiversity, water and soil cleaning, shade, carbon sequestration and cooling impacts.


Capture, store, and filter water efficiently into the ground while sequestering pollutants.


Bioswales direct rain and storm water to controlled locations in order to be captured, reducing flooding of impervious surfaces. They are attractive and require little to no maintenance. Bioswales are implementable on many different scales including the individual level. Bioswales can be built to divide pedestrians and cyclists from vehicular traffic, increasing everyone's safety. Their natural beauty increases community health and prosperity.


Sunlight, areas with high percolation rates, access to water runoff

Development Considerations

Percolation rates should be greater than 1 in/hour. A parabolic or trapezoidal shape is best with side slopes no deeper than 3:1. Graded side slopes, generally less than 2ft in depth a minimum bottom width of either 12 or 18 in. Maybe need a physical barrier ( grate, fence, high vegetation) to reduce injury risk among pedestrians and cyclists. Underground utilities may prevent space capacity.

Environmental Considerations

Native and ecologically suitable plants are extremely important. Water table needs to be considerably below the level of the bioswale. Rock or a grated pathways over biorientation area allow better accessibility to roads.

Maintenance Consideration

Maintenance is minimal due to native plants ability to self regulate. However, invasive plants need to be removed regularly and underdrains become clogged frequently. First years of implementation requires regular maintenance to ensure effectiveness.

Cost Considerations

Vary greatly depending on size.

Case Studies

Cover of the Moffett Park Specific Plan Urban Ecology Report

Moffett Park Specific Plan Urban Ecology

The Moffett Park Technical Plan lays out a city wide redevelopment of green infrastructure and Nature-Based Strategies that create habitats and natural corridors in order to reduce climate impacts and positively impact the community.

Aerial image of a pathway with green infrastructure on both sides and housing surrounding it.

Street Edge Alternatives (SEA) Street Pilot

Seattle Public Utilities reconstructed an entire city street to include green infrastructure throughout. The infrastructure included bioswales, tree canopies, pervious pavement and more.

Example sketch of what the bioswale may look like with trees, rain and water catchment areas.

Happy Valley Bioswale

The Happy Valley Bioswale in Ventura, CA is a massive example of what bioswales can achieve. The bioswale, 300 ft long in a horse shoe orientation, treats water runoff from 36 acres of the surrounding urban environment.

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