A
detention basin or
retarding basin is an excavated area installed on, or adjacent to, tributaries of
rivers,
streams,
lakes or
bays to protect against
flooding 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. Some detention ponds are also "wet ponds" in that they are designed to permanently retain some volume of water at all times. 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.