Roadside Guide to Clean Water: Vegetated Swales
Vegetated Swales at a Glance
Vegetated swales, sometimes also called bioswales, are contoured land areas or ditches covered in plants. They are designed to collect stormwater runoff and move it away from areas where it can't soak into the ground, such as a road, parking lot, or rooftop. Some look like straight channels, and others like meandering natural streams. Vegetated swales are typically planted with native plants, but sometimes they are covered in only turfgrass. They are often constructed with specialized soils that can naturally treat stormwater runoff. Sometimes barriers called check dams are constructed across the swale to slow water movement into pools and increase infiltration during larger storm events. Bioswales are aesthetically pleasing and can be installed instead of underground storm sewers or as part of a larger stormwater system.
How Vegetated Swales Work
By intercepting water running off large paved and developed areas, bioswales help improve water quality in many ways. Vegetated swales collect and slow stormwater runoff so the water can be taken in by plants and soak into the soil instead of flowing into the street and down a storm drain. The plants and soil trap, absorb, and filter pollutants found in stormwater runoff. By controlling the movement of the stormwater runoff, bioswales help prevent erosion. This helps prevent sediment and other pollutants, such as nutrients and heavy metals, from entering waterways. All of this results in lower water treatment costs and better public health. By restoring groundwater and decreasing water discharged into local creeks and rivers, vegetated swales reduce flooding and improve public safety. The native grasses and perennials in vegetated swales provide habitat for wildlife, including insects and pollinators. The plants also enhance and beautify the area.
Community Benefits of Vegetated Swales
- Flooding: Mitigates flooding
- Stormwater: Reduces stormwater runoff
- Groundwater: Recharges groundwater
- Pollution: Reduces pollution
- Habitat: Provides wildlife habitat
- Landscape: Beautifies the landscape
You can expect to find vegetated swales in urban, suburban, and rural settings.
How to Recognize Vegetated Swales
In agricultural fields, swale-like structures called grassed waterways are often used to help control the movement of excess water that can cause erosion. Visit "Grassed Waterways" to find out more.
Photo by Bob Nichols, USDA Natural Resources Conservation Service.
