Detention or Retention?
Which One Is It?
Some terms and phrases used in the business of flood damage reduction seem to find their way through the public-at-large either being interchanged with similar terms or referred to altogether incorrectly.
DETENTION and RETENTION are two such terms.
Both detention basins and retention basins are ways in which flood damage reduction can be accomplished. Although the terms are sometimes used interchangeably, there are differences between them.
A DETENTION BASIN is an area where excess stormwater is stored or held temporarily and then slowly drains when water levels in the receiving channel recede. In essence, the water in a detention basin is temporarily detained until additional room becomes available in the receiving channel. Detention basins are used extensively in the Harris County region.
A RETENTION BASIN also stores stormwater, but the storage of the stormwater would be on a more permanent basis. In fact, water often remains in a retention basin indefinitely, with the exception of the volume lost to evaporation and the volume absorbed into the soils. This differs greatly from a detention basin, which typically drains after the peak of the storm flow has passed, sometimes while it is still raining. Additional uses for stormwater retention are to help recharge large underground water aquifers, a use that isn't practical in Harris County. Retention basins, for the sake of flood damage reduction, are not common in the Harris County region; they are popular in parts of the country that have soils more amenable to this type of flood damage reduction measure.
The short of it is this:
DETENTION is the temporary storage of excess stormwater.
RETENTION implies that stormwater is stored indefinitely.
Detention basins are engineered, constructed and utilized extensively within the Harris County Flood Control District drainage infrastructure. Retention is not. There are approximately 50 detention basins in operation with the District throughout Harris County, as well as hundreds of detention basins constructed by land development projects.