Bioretention Systems are shallow vegetated depressions, often referred to by a variety of names, such as bioinfiltration areas, biofilters, rain gardens, bioswales, or recharge gardens. They are very effective at removing pollutants and reducing stormwater runoff. These systems are designed to collect water in the depressions, where it ponds on the surface. This water is then used by the vegetation in evapotranspiration and infiltrated into the soil. Larger volume systems may be designed to include stone or sand beds for storage underneath the soil, in order to provide additional capacity.
Properly designed biorention practices mimic natural ecosystems through species diversity, density, and distribution of vegetation. The use of native species results in a system that is resistant to insects, disease, pollution, and climatic stresses.