BIOSWALE
INSIDE THE FLOODPLAIN | OUTSIDE THE FLOODPLAIN

What Is It?

Cost: $58 per linear ft; $20-30 per sq ft
Applications: Parking lots, road/sidewalk drainage, residential/commercial buildings. Can be used in combination with other stormwater best management practices. Easily built into existing sites, though new construction can more easily take advantage of natural terrain and design for directing stormwater flows.
Service Life: Extensive, depending on continued maintenance.

Bioswales are similar to bioretention cells and rain gardens but instead channel stormwater into a trough filled with vegetation, compost or mulch, and rubble to reduce runoff, increase infiltration, and remove pollutants. Bioswales are often positioned alongside roads and parking lots to capture runoff. The swale’s side slopes should not exceed 33%, and longitudinal slope should not exceed 4% unless check dams are used to reduce flow velocity. Bioswales typically cost less than traditional curb and gutter systems, though their efficacy is dependent on proper siting, design, and construction, as well as continued maintenance. Moreover, bioswales can be ineffective during and become damaged by large storms, as high velocity flows can overwhelm the swale and erode vegetation. Vegetation used in bioswales should be flood tolerant, erosion resistant, salt tolerant, and native when possible. Bioswales can be used in combination with other stormwater best management practices to manage high stormwater flows.

Regular maintenance is required to ensure continued effectiveness and system longevity, including regular mowing and reseeding, as well as inspections for erosion, weed control, and trash removal. Proper snow and sand removal are necessary to ensure that bioswales continue functioning after winters in cold areas.

Benefits

  • Uses natural processes to reduce stormwater runoff volume, rate, and pollutants and increase soil and groundwater infiltration
  • Green spaces can improve urban air quality, contribute to lower urban air temperatures, and be aesthetically pleasing
  • Can be easily retrofitted during any landscape modification or parking lot/street resurfacing
  • Construction and maintenance costs of bioswales are often lower than those of conventional stormwater management systems

Drawbacks

  • Not suitable for heavy stormwater flows. Swales can be overwhelmed by large storms, and vegetation can be eroded by high velocity flows
  • Careful landscaping and maintenance required; poor landscaping and maintenance can result in ineffective drainage and could attract pests

Regulatory Impacts and Requirements

A summary of potential regulatory touchpoints follows below.
Bioswale

Financing Options, Incentives, And Rebates

Additional Resources

Project Examples

SAMPLE OF SUPPLIERS

SOURCES

Photo credit: The image is part of the public domain and available on Wikimedia Commons