An Underground Water Detention Structure Helps in Control of Stormwater Runoff
An excess of stormwater on a developed site can result in floods or other inconveniences. Stormwater detention vaults can function as an underground water detention system that can greatly help to provide the best management practice for stormwater.
These structures, largely built underground, help to manage and control the stormwater that would otherwise flow to nearby surface waters and cause erosion or flooding in streams and rivers. You can even have such structures built over the ground in the form of detention ponds that will temporarily store the stormwater so that it prevents localized flooding. These structures, detention vaults or detention ponds, also serve to help in reducing pollution as they can be made to act as settling basins that allow dirt and debris to settle in them before the excess water is led into natural courses.
During storms, impervious surfaces in built-up areas result in runoff that goes into waterways or storm sewers. When the storm event is large, the volume of runoff moves at increased rates, and this increases the potential for flooding in downstream areas, as well as act to erode watercourses. These detention ponds or vaults act as a temporary store for stormwater runoff, and this help to reduce the peak rate of runoff to streams or even storm sewers. This goes a long way in preventing localized flooding, reduces erosion of stream banks downstream, and also produces some water quality benefits.
These underground and overground water detention systems are designed to release all the water that they have captured over a period of time, and are not meant to act as permanent pools of water. The captured run-off can be released through outlet structures that can be pipes, weirs, orifices or risers, and their design provides for increased discharge from them as the water level in them increases. Extending the detention time for the water to remain in these structures allows for increased sedimentation of pollutants that improves the quality of water being discharged from them.
These water detention systems have to be downgradient to the built-up area and their floors need to be at least a couple of feet over the high water table, as otherwise groundwater can seep into them and reduce their capacity. These structures need to be at a fair distance from property lines so that this detained water does not have any effect on adjacent properties. For the same reason, they must also be at a substantial distance from wells and septic tanks.
An underground water detention system is primarily meant to delay the release of stormwater runoff, and need to be designed for the eventual release of the retained water. You can also have detention ponds that allow the water to infiltrate into the ground, while only the excess is allowed to drain out after the water has reached a certain level.
Underground vaults can be located under parking lots and this allows the entire developed plot area to serve the purpose behind the development. Detention ponds will result in a reduction of the land area in the property that can be used.