Stormwater Control Measures: Bioretention

Also known as a rain garden, a bioretention basin is a depression that has been filled with native plantings, a special soil mix, and landscape material. It is strategically located on a property to collect and treat stormwater runoff from developed (impervious) areas such as parking lots and rooftops.

More information on this Green Infrastructure Practice, along with a list of native plants for bioretention, can be found in the Stormwater Management Manual GIP-01 Bioretention.

Bioretention Flow Graphic

Graphic showing how bioretention works. Stormwater runoff from rain flows into the bioretention. Water evaporates, water soaks into the special soil mix, and plants in the bioretention use the water. Possible underdrains in the soil allow the water to flow to the stormwater system or a stream.

Graphic showing how bioretention works. Stormwater runoff flows into the bioretention cell where most of the water infiltrates into an engineered soil made of sand, fines, and organic matter. Then the biological process of evapotranspiration occurs through plants within the cell. Excess water soaks into the surrounding soils and/or flows through underdrains to the stormwater conveyance system. Excess water from large storm events will safely flow out of the basin through the designated overflow structure.

Maintenance

Property owners are responsible for inspecting and maintaining stormwater control measures on their property.

Inspection and maintenance requirements for your specific stormwater control measure are filed with your property deed. These documents are available through the Metro Nashville Register of Deeds.

Typical inspection and maintenance concerns

Observe the bed. Do the plants look healthy? Is there any erosion? Is there any trash? Does the mulch or stone need to be replaced? If so, the old layer of mulch or stone should be removed as to not reduce ponding volume.
Inspect the outlet and inlets to ensure there is no sediment, trash, and/or vegetation growth which could result in a clogged outlet or inlet and improper draining.
Is there evidence of water bypassing the bioretention basin?
Visit the bioretention site within 48 hours of a rain storm, and see if there is ponding. If so, maintenance may be required.
Avoid fertilizers and pesticides
Avoid possibly compacting soil by not using heavy equipment, such as riding lawnmowers, on the basin
If maintenance needs are identified during the inspection, ensure that service is performed in a timely manner to prevent larger problems from occurring in the future.