Extention basin

An extention basin or extension basin is a composite of a stormwater detention basin and other stormwater storage basins, linked by defined flow control panels and bypass systems. While the detention basin portion is used to control peak flows, the other stormwater storage basins are usually used for treatment of pollutants in stormwater, or for the reduction in stormwater runoff by infiltration. It was discovered in 2001 that the total storage volume for all the basins can be computed and then minimized by high-level, mathematical optimization procedures in addition to standard hydraulic principles.
The EPA has deemed that pollutants in stormwater have an adverse impact on streams, river, lakes and ponds, therefore, the federal government, in the Clean Water Act amendments, has required every State to comply with water quality standards leading to State Regulations, for example, in , California, to control both stormwater peak flows and stormwater quality. The extention basin is a structural measure that allows developers to meet the State Stormwater rules. It operates, typically, over storm frequencies in the range of 1 year to 100 year but there is no limit to the actual range of operation.
The extention basin is desirable since it minimizes total storage while performing the same detention functions. A detention basin stores flow and releases a small portion of the flow over time. The extention basin performs the same function but uses less land area than a detention basin. In the example in the image, the conventional detention basin requires substantially more storage, as can be seen by the larger difference between the falling limbs of the existing and final outflow hydrographs.
An additional characteristic of the extention basin is its ability to provide output hydrographs whose shape and time to peak is very close to the natural drainage basin timing prior to the land use changes (see Image). As a result, the extention basin can be used to make proposed land use changes nearly hydrologically transparent in the drainage system.
Detention basins are used worldwide (e.g. French studies) to control peak flows where flooding must be controlled though the extention basin is only evident in the United States as of 2010.

Main Menu

See Also

Main Menu