What is a bioretention area?

A bioretention area, also called a rain garden, is a stormwater treatment system that is a depression integrated into the landscape.

How does a bioretention area work?

A bioretention area captures runoff from an impervious surface and allows that water to infiltrate through the soil media. As the water infiltrates, pollutants are removed from the stormwater runoff through a variety of mechanisms including adsorption, microbial activity, plant uptake, sedimentation, and filtration. Some of the incoming runoff is temporarily held by the soil of the bioretention area and later "leaves" the system by way of evapotranspiration or exfiltration to the ground water. Specific information on pollutant removal processes can be found in publications. An animation depicting the overall process can be viewed here.

How effective are they at removing pollutants?

Bioretention areas have been found to remove metals, nutrients, sediment, and fecal coliform, provided they are situated, designed, constructed, and maintained appropriately. For more information on pollutant removal, please visit our publications page.

Can I construct one for my home?

Yes! In many cases, rain gardens (or simple bioretention areas) can be incorporated into a yard landscape without much difficulty. Visit the Backyard Rain Gardens site for more information.