Detention basin

Functions and design

Detention basins are storm water best management practices that provide general flood protection and can also control extreme floods such as a 1 in 100-year storm event. The basins are typically built during the construction of new land development projects including residential subdivisions or shopping centers. The ponds help manage the excess urban runoff generated by newly constructed impervious surfaces such as roads, parking lots and rooftops.

A basin functions by allowing large flows of water to enter but limits the outflow by having a small opening at the lowest point of the structure. The size of this opening is determined by the capacity of underground and downstream culverts and washes to handle the release of the contained water.

Frequently the inflow area is constructed to protect the structure from some types of damage. Offset concrete blocks in the entrance spillways are used to reduce the speed of entering flood water. These structures may also have debris drop vaults to collect large rocks. These vaults are deep holes under the entrance to the structure. The holes are wide enough to allow large rocks and other debris to fall into the holes before they can damage the rest of the structure. These vaults must be emptied after each storm event.

Research has shown that detention basins built with real-time control of the outflow from the basin are significantly more effective at retaining total suspended solids and associated contaminants, such as heavy metals, when compared to basins without control.

Extended detention basin

A variant basin design called an extended detention dry basin can limit downstream erosion and control of some pollutants such as suspended solids. This basin type differs from a retention basin, also known as a "wet pond," which includes a permanent pool of water.

While basic detention ponds are typically designed to empty within 6 to 12 hours after a storm, extended detention (ED) dry basins improve the basic detention design by lengthening the storage time, for example, to 24 or 48 hours. Longer detention allows for more settling of suspended solids, resulting in higher-quality water.

References

References

1. (December 2021). "Dry Detention Ponds". U.S. Environmental Protection Agency.
2. Atlanta Regional Commission. Atlanta, GA. [http://www.georgiastormwater.com/vol2/3-4-1.pdf "Georgia Stormwater Management Manual."] {{webarchive. link. (2008-04-10 Section 3.4.1: "Dry Detention / Dry ED Basins." August 2001.)
3. March 04. "Green Infrastructure: How to Manage Water in a Sustainable Way".
4. Dykehouse, Terry, P.E. Jones and Edmunds, Gainesville, FL.[http://www.florida-stormwater.org/pdfs/pondsarticle.pdf "Retention Ponds and Detention Ponds, The Recovery Process."] {{webarchive. link. (2008-04-10)
5. "Enviro-Stormwater Management".
6. "Ecohydraulic-driven Real-Time Control of Stormwater Basins". Universite Laval.
7. 1-57278-039-8. Chapter 5.
8. James Worth Bagley College. [https://wayback.archive-it.org/all/20080410222514/http://www.abe.msstate.edu/csd/p-dm/all-chapters/chapter4/chapter4/det-basin.pdf "Detention Basins."] Chapter 4: Best Management Practices. Agricultural and Biological Engineering, College of Agriculture and Life Sciences.
9. Minnesota Pollution Control Agency. [http://proteus.pca.state.mn.us/publications/swm-ch5.pdf "Stormwater Detention Ponds."] {{webarchive. link. (2008-04-10 Chapter 5, Minnesota State Permit Guidance Document.)