Product Code Database
A detention basin or retarding basin is an excavated area installed on, or adjacent to, tributaries of , , or to protect against and, in some cases, downstream erosion by storing water for a limited period of time. These basins are also called dry ponds, holding ponds or dry detention basins if no permanent pool of water exists.
Detention ponds that are designed to permanently retain some volume of water at all times are called . In its basic form, a detention basin is used to manage water quantity while having a limited effectiveness in protecting water quality, unless it includes a permanent pool feature.
A basin functions by allowing large flows of water to enter but limits the outflow by having a small opening at the lowest point of the structure. The size of this opening is determined by the capacity of underground and downstream and washes to handle the release of the contained water.Dykehouse, Terry, P.E. Jones and Edmunds, Gainesville, FL. "Retention Ponds and Detention Ponds, The Recovery Process."
Frequently the inflow area is constructed to protect the structure from some types of damage. Offset concrete blocks in the entrance spillways are used to reduce the speed of entering flood water. These structures may also have debris drop vaults to collect large rocks. These vaults are deep holes under the entrance to the structure. The holes are wide enough to allow large rocks and other debris to fall into the holes before they can damage the rest of the structure. These vaults must be emptied after each storm event.
Research has shown that detention basins built with real-time control of the outflow from the basin are significantly more effective at retaining total suspended solids and associated contaminants, such as heavy metals, when compared to basins without control.
While basic detention ponds are typically designed to empty within 6 to 12 hours after a storm, extended detention (ED) dry basins improve the basic detention design by lengthening the storage time, for example, to 24 or 48 hours. Longer detention allows for more settling of suspended solids, resulting in higher-quality water.
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