A simple and effective way to add pretreatment to any Biofiltration area is with the Rain Guardian™ .
Rain Guardian™ keeps trash, leaves and other debris out LID/GI Systems such as swales, filtration basins, infiltration basins, and bioretention systems. Rain Guardian simplifies maintenance by collecting sand, leaves, grass clippings, and other debris in a confined location. Rain Guardians make pretreatment maintenance quick and easy, while improving the water quality benefits of treatment practices. With efficient, simplified maintenance, Rain Guardians are a must for any rain garden.
Typical inlet options for BMPs include grass filter strips and rock inlets (see pictures to right), which are prone to erosion, require hours of maintenance, provide little or no pretreatment, and can actually cause water to bypass the practice because of their likelihood of clogging with debris. Properly designed dry filter boxes provide a stable inlet to the BMP, pretreat stormwater, drain and dry between rain events, and simplify maintenance by capturing sediment and debris in a chamber that requires less than five minutes to clean. It is important to note that a dry filter box is a maintenance tool for a BMP rather than a stand-alone BMP.
Dry filter boxes are positioned near the inlet of the BMP. Stormwater is most commonly directed into the dry filter box via a curb-cut and concrete inlet. Four stages of treatment provide effective removal of sediment and debris. Water first passes through a top grate, which captures leaf litter and coarse debris and then enters a main chamber where settling of heavier particles occurs. Even after the BMP fills to capacity, inundating the filter box, the top debris walls restrict floatable debris (e.g. leaf litter, seeds, garbage) from entering or exiting the BMP. A vertical filter wall contained within the dry filter box provides filtration of the stormwater and allows the chamber to drain and dry between rain events.
The dry filter box is a maintenance tool, while the BMP provides the desired water quality and water quantity benefits. All material captured by the dry filter box is contained in an easy to access and clean location right at the inlet of the BMP, allowing the BMP to function and provide water quality benefits as originally designed.