Definition  
In Sustainable Landscape Construction, the authors define Parking lot bioswales as “linear, planted drainage channels [that] move stormwater runoff as slowly as possible along a gentle incline, keeping the rain on the site as long as possible and allowing it to soak into the ground”. Different systems may be used in accomplishing this goal; the most common are biofiltration swales and filter strips, defined below.

Biofiltration swale:
Vegetation lined channel where water flows at a shallow depth and relatively slow velocity through vegetation but generally does not infiltrate. Best suited to treat runoff that has been collected and concentrated, such as at the outfall to a peak rate runoff control facility.

Filter strips:
Areas covered by vegetation over which dispersed runoff sheet flows at a very shallow depth. Filter strips are well suited to treating runoff from impervious areas such as parking lots, where frequent gaps in the curb provide dispersed inflow points to the filter strip.

Rain garden:
Unlike a biofiltration swale, a rain garden retains water and allows for infiltration. Water is cleansed by vegetation and soil systems.

Note: Some newer technologies, such as the Stormwater Treatment Train, are referenced at the end of this document.