A USDOT University Transportation Center

Detention and Retention Ponds

Detention and retention ponds, or basins, are common stormwater management methods that are used for flood control and diverting runoff.1,2 A retention (wet) basin has a permanent pool of water, while a detention (dry) basin is not always full with water. Detention ponds hold runoff for a short period of time, typically after a rain storm, and remain dry between storms. Dry detention ponds reduce runoff velocity and allows the water to be slowly released from the basin in order to prevent flooding. However, detention ponds do not typically improve water quality as well as retention ponds. Retention ponds maintain a pool of water and hold excess runoff following storms. These structures hold water for a longer period of time and allow finer pollutants to settle at the bottom. Wet retention ponds can naturally process water, create aquatic habitats, and be used recreationally.

Considering this strategy will help achieve the goal of the following objectives

  • Less Contamination
  • Less Emissions
  • Less Traffic Noise
  • Connectivity and Inclusion
  • Healthy Destinations
  • Less Traffic Violence
  • Active Transportation
  • Green Space

Transportation lifecycle phases

This strategy is associated with the following transportation lifecycle phases:

  • Construction
  • End of Life
  • Maintenance
  • Material Selection
  • Operations
  • Policy and Planning
  • Project Development

Who's involved

  • Drainage engineers
  • MPOs
  • Private developers

Detention and retention ponds, or basins, are common stormwater management methods that are used for flood control and diverting runoff.1,2 A retention (wet) basin has a permanent pool of water, while a detention (dry) basin is not always full with water.

Detention ponds hold runoff for a short period of time, typically after a rain storm, and remain dry between storms. Dry detention ponds reduce runoff velocity and allows the water to be slowly released from the basin in order to prevent flooding. However, detention ponds do not typically improve water quality as well as retention ponds.

Retention ponds maintain a pool of water and hold excess runoff following storms. These structures hold water for a longer period of time and allow finer pollutants to settle at the bottom. Wet retention ponds can naturally process water, create aquatic habitats, and be used recreationally.

How it Helps

As stormwater moves across roadways, driveways, and other surfaces, it can become polluted with various substances and is carried into waterways. Impervious structures, like concrete, do not allow for the absorption or treatment of runoff. However, retention ponds are an effective solution to control runoff quality by removing certain pollutants.3 By diverting and holding runoff into basins, detention and retention ponds can also prevent costly erosion and flooding consequences.

Implementing

Cost Considerations:

When deciding to construct either a retention or detention pond as a stormwater management strategy, it is important to consider the cost. Typically, detention basins are less expensive to implement due to their smaller size.1

Design Characteristics:

Both detention and retention ponds have advantages and disadvantages related to their design. Retention ponds require a large amount of land and may negatively impact water quality if they are improperly designed.2 Additionally, detention ponds may foster mosquito breeding grounds and decrease property value.1

Maintenance:

Detention and retention basins and the surrounding vegetation should be regularly maintained to ensure that water flow does not become blocked with debris.3 The basins should also be inspected for erosion damage and sediment buildup.

Examples

1) Denmark Study on Pollutant Removal Techniques

A Danish study that analyzed pollutant removal techniques for urban and highway runoff found that wet retention ponds are among the most effective and sustainable solutions. The study analyzed suspended solids, phosphorus, and heavy-metal removal percentages.

https://doi.org/10.1016/0048-9697(94)90275-5

1. Leber, B. (2015). Stormwater Basins: How Detention and Retention Ponds Work. Wessler Engineering. https://info.wesslerengineering.com/blog/stormwater-basins-detention-retention-ponds
2. TrapBag. Stormwater Containment. https://trapbag.com/stormwater-containment/
3. Sustainable Stormwater Management. (2009). Stormwater 101: Detention and Retention Basins. https://sustainablestormwater.org/2009/05/28/stormwater-101-detention-and-retention-basins/