Strengths

  • Traps and breaks down common pollutants.
  • Improves water quality in surrounding waterbodies using soil, vegetation and microbes.
  • Reduces stormwater runoff and increases infiltration and groundwater recharge.
  • Increases green space and aesthetic appeal.
  • Provides habitat for aquatic and other wildlife.
  • Can be easily retrofitted during any landscape modification or parking lot/street resurfacing.
  • Construction and maintenance costs are often lower than those of conventional systems.

Limitation

  • A bioswale is primarily a conveyance system and must be designed to transport water of a specific storm severity without flooding.
  • Regular inspection of bioswales should be conducted to identify signs of erosion, accumulation of debris around structures and signs of excessive sedimentation.
  • Should not be installed in areas with high water tables where groundwater reaches the bottom of the swale.
  • Protects both the toe of slope and bank from the erosive force of water.
  • Impractical for areas with very flat grades or steep slopes.

Bioswale

Application: Aquifers, bridge abutments, drainage, roads, footpaths, stormwater outfall, wastewater treatment plants

Description: Bioswales are stormwater runoff conveyance systems that collect, infiltrate and treat stormwater runoff before releasing it to the watershed or storm sewer. They are linear ditches filled with vegetation, compost and/or riprap. The water flow path, along with the wide and shallow ditch, is designed to maximize the time water spends in the swale, which aids the trapping of pollutants and silt. The vegetation reduces water velocity, allowing it to accumulate in a bioswale, and filters suspended sediments. Microbes in the soil digest organic nutrients. The water then moves to another filtration level made of sand or rocks. If bioswales are constructed on porous soils, the stormwater detained in the trenches can infiltrate into the ground below. This allows the rainwater to recharge the groundwater below rather being flushed into the sewer system. Bioswales may be designed to contain check dams that facilitate pond formation, further increasing infiltration and decreasing stormwater flow.

Contribution to climate resilience: Bioswales detain stormwater before it is infiltrated or discharged downstream, thus improving water quality (by removing pollutants) and reducing erosion and other damage associated with runoff. They thus reduce the negative impacts of heavier rainfall and storms, which are expected to increase (in the wet season) with climate change.

Supplementary sources of information:

http://www.esf.edu/ere/endreny/GICalculator/BioswaleIntro.html

http://greencampsinitiative.org/wp-content/uploads/2015/04/bioswales1.pdf

http://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs144p2_029251.pdf

https://www.soils.org/discover-soils/soils-in-the-city/green-infrastructure/important-terms/rain-gardens-bioswales

https://www.columbus.gov/Templates/Detail.aspx?id=53960

Background image credit: Flickr

This resilience-building measure is sourced from the Water Resource Adaptation Guide (2019) published by the National Council for Sustainable Development at the Ministry of Environment in Cambodia. The full Guide is available to download at URL https://ncsd.moe.gov.kh/sites/default/files/2019-10/Water%20Resources%20Adaptation%20Guide_March%202019_En.pdf