Stormwater Control Measures: Wet Detention Pond

Also known as wet ponds, retention ponds are designed with a permanent pool of water to facilitate the treatment of stormwater. These ponds prevent downstream flooding and allow sediment, nutrients, heavy metals, and other pollutants, to settle out. Deep pools of water, micropools, and shallow marshes, are three common types of retention ponds.

More information on this Green Infrastructure Practice can be found in the Stormwater Management Manual.

GIP-06 Extended Detention

Wet Detention Pond Flow Graphic

Graphic showing how a wet retention pond works. Stormwater runoff from rain flows into the grass-covered wet pond through a pipe. Some water evaporates. Water stays in the pond. There is an overflow structure. When the pond is full, water overflows to a stream.

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. Small storms are usually retained within the pond and do not discharge through the outlet/overflow structure.

Maintenance

Property owners are responsible for inspecting and maintaining SCMs on their property.

Inspection and maintenance requirements for your specific SCM are filed with your property deed. These documents are available through the Metro Nashville Register of Deeds.

Typical inspection and maintenance concerns

Inspect for signs of erosion on the banks and ditches feeding and draining from pond.
Inspect the outlet structure for clogs and other functional or structural issues.
Look for trash or sediment build up within the pond.
For wet ponds with impermeable rubber liners, look for areas where the liner is washing out of the banks of the pond, especially near the water’s edge. Check for damage to any exposed liner either on the bank or within the basin.
Inspect the forebay area. Is there a lot of sediment accumulated? If the forebay is full of sediment, then your pond will eventually fill with sediment too.
Inspect the dam around the pond. Is it overgrown with woody vegetation (trees or shrubs)? Are there areas of seepage? Is there evidence of burrowing animals, such as groundhogs or muskrats?
If maintenance needs are identified during the inspection, ensure that service is performed in a timely manner to prevent larger problems from occurring in the future.