Slide 38 of 52
Notes:
Bioretention is a design variation of filtering practices that warrants special discussion due to subtle, yet important, differences in design criteria. The bioretention concept was originally developed by the Prince George's County, Maryland, Department of Environmental Resources in the early 1990's as an alternative to traditional stormwater treatment structures. Bioretention treats stormwater runoff using a conditioned planting soil bed and planting materials to filter runoff stored within a shallow depression. The method combines physical filtering and adsorption with biological processes. The system consists of a flow regulation structure, a pretreatment filter strip or grass channel, a made sand bed, pea gravel overflow curtain drain, a shallow ponding area, a surface organic layer of mulch, a planting soil bed, plant material, a gravel underdrain system, and an overflow system.
While the land consumed by bioretention is relatively high compared with other filtering practices (5 to 10% of the impervious cover draining to it), bioretention typically replaces traditional landscaping that would have occupied this space. In addition, regular maintenance can be provided by commercial landscaping companies, and the �planting hole� provided by the bioretention area often increases the survival rates of landscaping as compared with traditional parking lot islands.
