Bioretention is a soil and plant-based stormwater management best management practice (BMP) employed to filter runoff from developed communities. Bioretention is a critical component of Low Impact Development (LID). LID is a philosophy of development in which steps are taken to maintain predevelopment hydrology, as near a possible. All green space is made functional to keep storm water onsite, to minimize runoff by maximizing infiltration, and to employ natural processes for the minimization of runoff.
Also known as a rain garden, a bioretention facility consists of a porous soil covered with a thin layer of mulch. A stand of various grasses, shrubs, and small trees is established to promote evapotranspiration, maintain soil porosity, encourage biological activity, and promote uptake of some pollutants. Runoff from an impervious area is directed into the bioretention facility. The water infiltrates through the plant/mulch/soil environment, providing the treatment.
Typically, bioretention practices are integrated throughout a land development project and are strategically placed to intercept runoff near the source. Originally designed to provide an element of water quality control, recent studies have shown that quantity control can be achieved as well. Bioretention systems function similar to infiltration/filtration practices with the added advantage of aesthetically pleasing landscaping in the form of a dense vegetative cover.
Bioretention systems can be designed to mimic natural hydrologic processes that occur in vegetated areas to absorb and filter water through evapotranspiration and soil filtering mechanisms. Through wastewater treatment experiences and literature research, it has long been recognized that soils and plant materials can successfully filter pollutants from water.
