Detention Retention Systems
Two different kinds of ponds are often used for flood control and stormwater runoff treatment:
wet ponds and dry ponds. Both systems function to settle suspended sediments and other solids
typically present in stormwater runoff. Wet ponds are also called retention ponds and they hold
back water similar to water behind a dam. The retention pond has a permanent pool of water that
fluctuates in response to precipitation and runoff from the contributing areas. Maintaining a pool
discourages resuspension and keeps deposited sediments at the bottom of the holding area.
Detention ponds are more common in the arid west and serve as important flood control
features. They are usually dry except during or after rain or snow melt. Their purpose is to slow
down water flow and hold it for a short period of time such as 24 hours. Urban areas rely on these
structures to reduce peak runoff rates associated with storms, decreasing flood damage.
