Slide 1 of 52
Stormwater filtering systems refer to a diverse group of techniques that treat stormwater runoff for water quality. One common thread is that each utilizes some kind of filtering media, such as sand, soil, gravel, peat or compost to filter pollutants entrained in stormwater runoff. Second, filtering systems are typically applied to small drainage areas (five acres or less). Third, filtering systems are designed solely for pollutant removal. Flows greater than the water quality treatment volume are bypassed around the filter to a downstream stormwater management facility. Filtering systems incorporate the following four basic design components in every application: (a) inflow regulation that diverts a defined flow volume into the system; (b) a pretreatment technique to capture coarse sediments; (c) the filter bed surface and unique filter media, and (d) an outflow mechanism to return treated flows back to the conveyance system and/or safely handle storm events that exceed the capacity of the filter.
This slide show presents basic design guidance for stormwater filtering systems, which include surface sand filters, perimeter filters, organic filters, underground filters, pocket sand filters, and bioretention. The design criteria are similar for all of the variations of filters. For a more detailed discussion, please refer to the 1996 Center for Watershed Publication entitled: “Design of Stormwater Filtering Systems.”