Wet ponds consist of a permanent pool of standing water that promotes a better environment for gravitational settling, biological uptake and microbial activity. Runoff from each new storm enters the pond and partially displaces pool water from previous storms. The pool also acts as a barrier to re-suspension of sediments and other pollutants deposited during prior storms. When sized properly, wet ponds have a residence time that ranges from many days to several weeks, which allows numerous pollutant removal mechanisms to operate. Wet ponds can also provide extended detention (ED) above the permanent pool to help meet channel protection requirements.
Designers should note that a wet pond is the final element in the roof-to-stream runoff reduction sequence, so one should be considered only if there is remaining Treatment Volume or Channel Protection Volume to manage after all other upland runoff reduction options have been considered and properly credited. Wet ponds may be allowed in certain coastal plain situations where the water table is within 3 feet of the ground surface.