Difference between revisions of "Category:Level 3 - General information, reference, tables, images, and archives/Tables/Swales"

Category:Level 3 - General information, reference, tables, images, and archives/Tables/Swales

Photo of a dry swale. Courtesy of Limnotech.

Photo of a wet swale. Courtesy of Limnotech.

Stormwater step pool. Courtesy of Limnotech.

Swales are linear features that convey water but can be configured to address water quality and quantity and perform additional functions. There are three types of swale addressed in this manual.

• Dry swales, sometimes called grass swales, are similar to bioretention cells but are configured as shallow, linear channels. Dry swales function primarily as a conveyance BMP, but provide treatment of stormwater runoff, particularly when used in tandem with check dams that temporarily retain water in a series of cells. Dry swales with an underdrain and engineered soil media are considered a filtration. Dry swales with in-situ soils capable of infiltration, (A or B soils) are considered infiltration practices. Dry swales are designed to prevent standing water. Dry swales typically have vegetative cover such as turf or native perennial grasses.
• Wet swales occur when the water table is located very close to the surface or water does not readily drain out of the swale. A wet swale acts as a very long and linear shallow biofiltration or linear wetland treatment system. Wet swales do not provide volume reduction and have limited treatment capability. Incorporation of check dams into the design allows treatment of a portion or all of the Water Quality Volume within a series of cells created by the check dams. Wet swales planted with emergent wetland plant species provide improved pollutant removal. Wet swales may be used as pretreatment practices. Wet swales are commonly used for drainage areas less than 5 acres in size.
• Stormwater step pools are defined by design features that address higher energy flows due to more dramatic slopes than dry swales or wet swales. Using a series of pools, riffle grade control, native species vegetation and a sand seepage filter bed, flow velocities are reduced, treated, and, where applicable, infiltrated. The physical characteristics of the stormwater step pools are similar to Rosgen A or B stream classification types, where “bedform occurs as a step/pool, cascading channel which often stores large amounts of sediment in the pools associated with debris dams” (Rosgen, 1996). These structures feature surface/subsurface runoff storage seams and an energy dissipation design that is aimed at attenuating the flow to a desired level through energy and hydraulic power equivalency principles (Anne Arundel County, 2009). Stormwater step pools are designed with a wide variety of native plant species depending on the hydraulic conditions and expected post-flow soil moisture at any given point within the stormwater step pool.

This page (Category) provides links to tables that provide information on swales.