Dry and Wet Swales Sizing Criteria
Length, width, depth, and slope required to accommodate the WQV
Outlet structures sized to release WQV over 24 hours
Maximum depth of 18” for water quality volume, 12” average depth
Notes:
The detention/retention capacity of both dry and wet swales is governed by the runoff associated with the water quality storm. The swale length, width, depth, and slope should be designed to temporarily accommodate the WQv through surface ponding. For the dry swale, all of the surface ponding should dissipate within a maximum 24 hour duration. The outlet structure is sized to release the WQv over 6 hours. Using perforations in the bottom 6" of pipe. The soil media will have an infiltration capacity of at least a foot/day.
Swales should be designed to provide a shallow ponding depth for the WQv (a maximum depth of 18" for the WQv is recommended), safely convey the 2 year storm with design velocities less than 4.0 to 5.0 feet per second, and provide adequate capacity for the 10 year storm with a minimum of 6 inches of freeboard.