Detention & Retention

Stormwater detention basins are specifically designed and engineered to receive and temporarily hold large amounts of stormwater to protect areas from flooding.  Detention facilities can keep existing drainage systems from exceeding capacity.  New sites and development, which typically increase impervious surfaces and thus increase velocity of run-off, use detention basins to mitigate the effects of flooding.

Design

Storage facilities can be either constructed above ground or placed below ground as a vault. Buried vaults can be prefabricated concrete, corrugated aluminum, polyethylene, or fiberglass structures.  Design and performance criteria for stormwater detention and water quality treatment is typically found in the state and local water quality manuals.

Detention vs. Retention:  The Difference

DETENTION- short-term storage of stormwater.
The objective of a detention facility is to regulate the runoff from a given rainfall event and to control discharge rates to reduce the impact on downstream stormwater systems.

RETENTION– permanent storing of stormwater indefinitely.
Water is stored until it is lost through percolation, taken in by plants, or through evaporation.

Detention Design Models & Tools