Bioretention & Rain Gardens

Bioretention areas are shallow stormwater basins that utilize engineered soils and vegetation to capture and treat stormwater runoff. They are utilized to capture stormwater runoff from relatively small areas of impermeable surface (< 5 acres).

Bioretention areas typically consist of a ponding area covered by an organic or mulch layer with native herbaceous and woody plant installed in an engineered planting soil bed. Water flows from the contributing drainage area through a grassed strip to the ponding area.

Under the planting bed, gravel and perforated pipe underdrain carry water away that has filtered through the bed. Areas with high infiltration soil may not require this under-drain system.

Residential bioretention areas, usually known as rain gardens, may be constructed by excavating a small depression to hold and infiltrate water from downspouts, driveways or other impervious surfaces.

In all bioretention areas, deep rooted native grasses and sedges should be utilized to prevent erosion and increase infiltration.

View a list of herbaceous species applicable to bioretention basins:

• Downloadable Specifications
• Plant List