Extended detention ponds Depressed basins that temporarily store a portion of stormwater runoff following a storm event. May be berm-encased area, excavated pond or tank. Water is controlled by means of a hydraulic control structure to restrict outlet discharge. Wet ponds Similar to the extended detention pond except that a permanent volume of water is incorporated into the design. Soluble pollutant removal is enhanced by biological processes.
Wet ponds can have aesthetic and recreational value, as well as offering flood-control benefits.
An excavated trench lined with a filter fabric and backfilled with stone to form an underground basin. Runoff is diverted to the trench and either exfiltrates into the soil, or enters a perforated pipe underdrain and is routed to an outflow facility. Smaller trenches are used for water quality, while larger trenches can offer stormwater quantity control. Infiltration basins Similar to infiltration trenches, except that they are generally used for larger drainage areas and water is stored in a visible pond. Normally designed to capture the first flush runoff volume for smaller catchments than extended detention ponds.