Dirtwork term
Detention Basin
also called: detention pond, dry pond
Excavated basin sized to temporarily hold stormwater and release it slowly to a downstream system.
A detention basin is a hole dug in the ground, sized to capture peak storm runoff from a watershed and release it slowly through a controlled outlet, usually a small pipe or weir. The point is to flatten the storm peak so downstream systems (creeks, storm sewers, culverts) don't get overwhelmed.
Unlike a retention pond, a detention basin is usually dry between storms, it fills during heavy rain and empties within 24 to 72 hours. Required on most commercial site developments and many subdivisions to satisfy city or county stormwater rules.
Sizing is by engineering calculation based on watershed acreage, expected storm return interval (10-year, 25-year, 100-year), and the allowed release rate. We dig to engineer-stamped quantities and elevations. Maintenance is a real ongoing item, sediment that drops out in the basin has to be removed every few years or storage volume is lost.
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Related terms
Other words that come up alongside this one
Retention Pond
Excavated pond that holds water permanently, with storage capacity above the normal pool for storm events.
Watershed
The area of land that drains to a single low point, every drop of rain that falls inside it ends up at the same place.
SWPPP
Federal/state-required plan for keeping sediment, debris, and pollutants out of waterways during construction.
Culvert
Pipe or box buried under a road, driveway, or fill that lets water pass from one side to the other.
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