Detention Pond
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Definition
A stormwater basin that temporarily holds runoff and releases it through an outlet structure at a controlled rate, draining to empty between storms. A retention pond, by contrast, holds a permanent pool of water.
Frequently Asked Questions
What is the difference between a detention pond and a retention pond?
A detention pond is dry between storms. It fills during a rainfall event and drains down through an outlet control structure, and its purpose is to limit peak discharge rate. A retention pond holds a permanent pool, releasing only through infiltration, evaporation, or a higher overflow, and it provides water quality treatment as well as rate control.
What controls how fast a detention pond drains?
The outlet control structure — usually some combination of an orifice plate, weir, or riser sized so the post-development peak discharge does not exceed the pre-development rate for the design storms. An emergency spillway handles events larger than the design storm.
Conclusion
Detention controls the rate at which stormwater leaves a site, which is what keeps development from pushing flooding downstream.
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