A detention basin is a structure which is designed to assist with flood control and water management. Detention basins can take a variety of forms, and can be seen in many regions of the world. They are often constructed during periods of new development, in which the amount of impermeable surfaces in an area is increased, potentially creating a flood risk which needs to be offset with a detention basin.
The purpose of a detention basin is to temporarily hold an overflow of water, thereby allowing water to accumulate in a safe, controlled area if unusual amounts of water are present. These structures can be useful for seasonal flood management as well as protection against rare serious storms. They are typically designed to fill and drain with the assistance of gravity, reducing the amount of maintenance required and ensuring that they will work without the need for electrical or mechanical systems.
Dry pond or dry detention basins are designed to be dry most of the time. They consist of recessed areas which may be lined with landscaping, with several inlets for water. As water starts to rise, it enters the inlets, filling the detention basin. Once water levels fall again, the water in the basin is gently pulled out. Often, filtration systems are installed to keep debris out, in which case it is important to periodically inspect the grates, gravel beds, or other filtering methods used to confirm that they are clear.
Retention basins, wet detention basins, or extended detention basins are all terms used for detention basins which stay wet year round. The water level in the detention basin can rise and fall over the course of the year, but some water always remains present. Marshy plants may also be present, creating habitat for animals and adding to flood control, as marshy areas can help contain floodwaters. This type of detention basin can also be used to manage water quality by trapping impurities before water is routed to another location.
These structures can be added to a community for flood control is flooding is an issue of concern, and they may also be constructed whenever new development occurs. In some regions, there are specific laws about how, where, and when detention basins are to be built, with the goal of keeping communities safe and reducing the risk of damage from flooding. In areas undergoing climate shift, building such structures can be especially critical for safety, to allow the community to keep up with changing rainfall levels.