Biofilters and bioswales are landscape elements designed to remove silt and pollution from surface runoff. Bioswales typically consist of a swaled drainage course filled with vegetation, compost, and/or riprap. They are designed to maximize the time water spends in them, aiding the trapping of silt and pollutants. A common application is around parking lots, which are used treat the parking lot runoff before releasing it to the watershed or storm sewer.
The following two documents provide excellent information on the design, construction, implementation, and maintenance of bioswales and other biofilter elements. These documents provide a practical approach for the stormwater engineer, allowing him to quickly implement these design elements into his engineering project designs.