Bioswales can improve water quality resources

The quality of local water resources is important to Michigan residents as part of a good quality of life, clean environment and strong economy.

This is a bioswale at the L.A. Zoo. By centering it, run off is collected from both sections of the parking lot.
This is a bioswale at the L.A. Zoo. By centering it, run off is collected from both sections of the parking lot.

For many years, Michigan’s lakes, rivers and streams were polluted to the point where many were not swimmable or fishable. Over the last decade, many of these water resources have seen remarkable improvement. Michiganders and tourists from other states are now attracted to Michigan waterways for their many recreational opportunities.

Precipitation can do three things when it lands on the ground during a rain, snow, hail or sleet event. Thinking back to grade school and the water cycle, we know it can evaporate back into the air, it can soak into ground becoming part of the groundwater found below the surface or it can run off directly into local rivers, streams, lakes and drainage ditches. Because water is a universal solvent, it picks up anything on the ground as it makes its way to the nearest surface water. That may be fertilizer, pesticides, oil, gas, trash. All of these go into our waterways along with the water runoff. As the amount of impervious surface increases (sidewalks, parking lots, driveways, roads, rooftops), the amount of land for infiltration decreases resulting in increased run off and potentially more pollution into our surface water.

A bioswale is one way to protect our surface waters by decreasing stormwater runoff. It is a gently sloping vegetative swale designed to slow and reduce stormwater runoff while filtering out pollutants. Bioswales are frequently placed at or near parking lots to capture pollutants from cars preventing it from being carried into nearby waterways after a storm. But bioswales can also be located near waterways to prevent stormwater runoff from entering there. The drainage path, along with the vegetation, is designed to maximize the amount of time stormwater remains in the bioswale. The longer stormwater can stay in the bioswale area, the more pollutants are filtered out.

The benefits of a bioswale on water quality include:

  • Protects local waterways from stormwater pollutants
  • Creates habitat for wildlife, including birds and butterflies,
  • Reduces non-point pollution by filtering stormwater
  • Reduces standing water (puddles) that can attract mosquitoes
  • Creates colorful gardens with a variety of flowers and plants year round
  • Requires little maintenance after establishment

Bioswales are usually planted with a variety of native plants. These are plants that have historically grown in the region. Native plants have deep roots so they can absorb stormwater and filter out pollutants, also known as “non-point source” pollution. Non-point source simply means the source of the pollutant cannot be easily identified. It can come from many sources. Point source pollution, conversely, means the pollution’s source can be identified, such as a failing septic system, a leaking storage tank, etc. Native plants also can create mini ecosystems that can provide food sources for wildlife and insects. Some common native plants that work well in bioswales include New England Aster, Red-twig Dogwood and Black-eyed Susan.

For more information on native plants, see Michigan State University Extension bulletin “Attracting Beneficial Insects with Native Flowering Plants” (E 2973) available at your County Extension office or online

Checkout the “Landscaping for Water Quality” booklet from the Department of Environmental Quality for more information on this topic. 

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