Detention basin
Encyclopedia
A detention basin is a stormwater
management facility installed on, or adjacent to, tributaries of river
s, stream
s, lake
s or bay
s that is designed to protect against flood
ing and, in some cases, downstream erosion
by storing water for a limited period of a time. These basins are also called "dry ponds", "holding ponds" or "dry detention basins" if no permanent pool of water exists. Some detention ponds are also "wet ponds" in that they are designed to permanently retain some volume of water at all times. In its basic form, a detention basin is used to manage water quantity while having a limited effectiveness in protecting water quality
, unless it includes a permanent pool feature.
(BMPs) that provide general flood protection and can also control extreme floods such as a 1 in 100-year storm event. The basins are typically built during the construction of new land development projects including residential subdivisions or shopping centers. The ponds help manage the excess runoff generated by newly-constructed impervious surfaces such as roads, parking lots and rooftops.
A basin functions by allowing large flows of water to enter but limits the outflow by having a small opening at the lowest point of the structure. The size of this opening is determined by the capacity of underground and downstream culvert
s and washes
to handle the release of the contained water.
Frequently the inflow area is constructed to protect the structure from some types of damage. Offset concrete
blocks in the entrance spillways are used to reduce the speed of entering flood water. These structures may also have debris
drop vaults to collect large rocks. These vaults are deep holes under the entrance to the structure. The holes are wide enough to allow large rocks and other debris to fall into the holes before they can damage the rest of the structure. These vaults must be emptied after each storm event.
such as suspended solids
. This basin type differs from a retention basin
, also known as a "wet pond," which includes a permanent pool of water, and which is typically designed to protect water quality.
While basic detention ponds are often designed to empty within 6 to 12 hours after a storm, extended detention (ED) dry basins improve on the basic detention design by lengthening the storage time, for example, to 24 or 48 hours. Longer storage times tend to result in improved water quality because additional suspended solids are removed.
Stormwater
Stormwater is water that originates during precipitation events. It may also be used to apply to water that originates with snowmelt that enters the stormwater system...
management facility installed on, or adjacent to, tributaries of river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
s, stream
Stream
A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...
s, lake
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
s or bay
Bay
A bay is an area of water mostly surrounded by land. Bays generally have calmer waters than the surrounding sea, due to the surrounding land blocking some waves and often reducing winds. Bays also exist as an inlet in a lake or pond. A large bay may be called a gulf, a sea, a sound, or a bight...
s that is designed to protect against flood
Flood
A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...
ing and, in some cases, downstream erosion
Erosion
Erosion is when materials are removed from the surface and changed into something else. It only works by hydraulic actions and transport of solids in the natural environment, and leads to the deposition of these materials elsewhere...
by storing water for a limited period of a time. These basins are also called "dry ponds", "holding ponds" or "dry detention basins" if no permanent pool of water exists. Some detention ponds are also "wet ponds" in that they are designed to permanently retain some volume of water at all times. In its basic form, a detention basin is used to manage water quantity while having a limited effectiveness in protecting water quality
Water quality
Water quality is the physical, chemical and biological characteristics of water. It is a measure of the condition of water relative to the requirements of one or more biotic species and or to any human need or purpose. It is most frequently used by reference to a set of standards against which...
, unless it includes a permanent pool feature.
Functions and design
Detention basins are storm water best management practicesBest management practice for water pollution
Best Management Practices is a term used in the United States and Canada to describe a type of water pollution control. Historically the term has referred to auxiliary pollution controls in the fields of industrial wastewater control and municipal sewage control, while in stormwater management ...
(BMPs) that provide general flood protection and can also control extreme floods such as a 1 in 100-year storm event. The basins are typically built during the construction of new land development projects including residential subdivisions or shopping centers. The ponds help manage the excess runoff generated by newly-constructed impervious surfaces such as roads, parking lots and rooftops.
A basin functions by allowing large flows of water to enter but limits the outflow by having a small opening at the lowest point of the structure. The size of this opening is determined by the capacity of underground and downstream culvert
Culvert
A culvert is a device used to channel water. It may be used to allow water to pass underneath a road, railway, or embankment. Culverts can be made of many different materials; steel, polyvinyl chloride and concrete are the most common...
s and washes
Arroyo (creek)
An arroyo , a Spanish word translated as brook, and also called a wash is usually a dry creek or stream bed—gulch that temporarily or seasonally fills and flows after sufficient rain. Wadi is a similar term in Africa. In Spain, a rambla has a similar meaning to arroyo.-Types and processes:Arroyos...
to handle the release of the contained water.
Frequently the inflow area is constructed to protect the structure from some types of damage. Offset concrete
Concrete
Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...
blocks in the entrance spillways are used to reduce the speed of entering flood water. These structures may also have debris
Debris
Debris is rubble, wreckage, ruins, litter and discarded garbage/refuse/trash, scattered remains of something destroyed, or, in geology, large rock fragments left by a melting glacier etc. The singular form of debris is debris...
drop vaults to collect large rocks. These vaults are deep holes under the entrance to the structure. The holes are wide enough to allow large rocks and other debris to fall into the holes before they can damage the rest of the structure. These vaults must be emptied after each storm event.
Extended detention basin
A variant basin design called an extended detention dry basin can limit downstream erosion and control of some pollutantsWater pollution
Water pollution is the contamination of water bodies . Water pollution occurs when pollutants are discharged directly or indirectly into water bodies without adequate treatment to remove harmful compounds....
such as suspended solids
Suspended solids
Suspended solids refers to small solid particles which remain in suspension in water as a colloid or due to the motion of the water. It is used as one indicator of water quality....
. This basin type differs from a retention basin
Retention basin
A retention basin is used to manage stormwater runoff to prevent flooding and downstream erosion, and improve water quality in an adjacent river, stream, lake or bay. Sometimes called a wet pond or wet detention basin, it is an artificial lake with vegetation around the perimeter, and includes a...
, also known as a "wet pond," which includes a permanent pool of water, and which is typically designed to protect water quality.
While basic detention ponds are often designed to empty within 6 to 12 hours after a storm, extended detention (ED) dry basins improve on the basic detention design by lengthening the storage time, for example, to 24 or 48 hours. Longer storage times tend to result in improved water quality because additional suspended solids are removed.
See also
- Best management practice for water pollutionBest management practice for water pollutionBest Management Practices is a term used in the United States and Canada to describe a type of water pollution control. Historically the term has referred to auxiliary pollution controls in the fields of industrial wastewater control and municipal sewage control, while in stormwater management ...
- Retention basinRetention basinA retention basin is used to manage stormwater runoff to prevent flooding and downstream erosion, and improve water quality in an adjacent river, stream, lake or bay. Sometimes called a wet pond or wet detention basin, it is an artificial lake with vegetation around the perimeter, and includes a...
- Stream restorationStream restorationStream restoration or river restoration, sometimes called river reclamation in the UK, describes a set of activities that help improve the environmental health of a river or stream. Improved health may be indicated by expanded habitat for diverse species and reduced stream bank erosion...
- Sustainable urban drainage systemsSustainable urban drainage systemsSustainable Drainage Systems , sometimes known as Sustainable Urban Drainage Systems , are designed to reduce the potential impact of new and existing developments with respect to surface water drainage discharges.-Background:...
- Sustainable Flood Retention Basin
- Balancing lakeBalancing lakeA balancing lake is a term used in the U.K. describing an element of an urban drainage system used to control flooding by temporarily storing flood waters...
External links
- Detention vs. retention - Project Brays (Harris County, Texas)
- Maintaining Your BMPs: A Guidebook for Private Owners & Operators in Northern Virginia