Bioswales are added to sites to remove silt and pollution from stormwater runoff. Similar to bioretention areas and rain gardens, bioswales are a variation of the traditional grassland swale seen throughout Broward County.
Bioswales consist of depressed land that serves as linear drainage areas. They are shallow, naturally or artificially formed ditches that are filled with vegetation, compost or another natural water filter. They are designed to maximize the time water spends traveling through them, which allows more contaminants to be trapped. Bioswales are different from traditional swales because a fabricated soil bed replaces the native soil with a sand/soil mix that meets permeability requirements. They also include native grasses and plants with deep root structures. These plants slow the flow of water and enhance filtration.
Bioswales are commonly used in parking lots, where water is filtered from the pavement into the depression and travels the length of the lot before being released into the watershed or a storm sewer.
- An increase in groundwater recharge because more water can infiltrate the soil.
- A reduction in the volume of runoff water on a site by almost 30 percent.
- Combined treatment and transportation of stormwater.
- An increase in the aesthetic value of yards and neighborhoods.
- Bioswales must be functional, maintainable and attractive to ensure long-term success.
- While similar in design, bioswales are more linear than bioretention areas or rain gardens, and are designed for conveyance.
- Only shallow slopes are effective. Steep slopes result in rapid travel and less filtration.
- Check for or consider installing dams that may enhance pollutant removal.
- They are primarily used for small sites and may not be effective on larger sites.
- Choosing the proper landscaping is critical to the performance of a bioswale:
- Select native vegetation with deep root structures.
- Select species that withstand the frequent and substantial water flow. Plants that can tolerate both wet and dry conditions may work best.
- Consider the flow path to maximize conveyance. Bioswales may be more linear or curvaceous, depending on site characteristics.
- Design the planting layout to allow for easy access and to facilitate periodic removal of sediments without significant disruption or removal of plant materials.
- A lack of consideration for these details can lead to failed plantings and site flooding.
See the Retrofit Considerations page for guidance when integrating bioswales into an existing water management system.
Bioswales divert stormwater from nearby impervious surfaces into a vegetated ditch that will filter out silt and pollution. Courtesy of Sue Donaldson, UNR Cooperative Extension
Incorporating functional green spaces into developments, like these infiltration gardens, increases property value and creates a more pleasant environment for living. Courtesy of Diana Guidry
The land is gently sloped away from the road to encourage water to percolate through the soil instead of overburdening a storm drain. Courtesy of Eric Livingston