Stormwater - Detention Basins |
How Detention Basins Work
Detention basins are located in or beside larger washes within the City of Sierra Vista (see Detention Basin Map). Detention basins work by capturing large amounts of fast moving water and releasing it slowly. This is accomplished by providing a large storage space for the water within the basin. Incoming water begins to fill the storage space within the basin during the first part of a storm. The basins are equipped with an outlet structure that releases the water more slowly than it comes in. As the storm progresses, the outlet structure causes the water to back up within the basin. When engineers design the basins, they are really performing a balancing act. They want to release the water as slowly as possible, but the more slowly it is released, the larger (and more expensive) the basin has to be. The designer has to balance these two components of the design to get the most efficient facility possible.
Detention basins help the community in two significant ways. As land is developed, the amount of impervious surface increases and the amount of vegetation decreases. Impervious surfaces are surfaces such as asphalt, concrete and rooftops that do not allow water to soak into the ground, which increases both the volume of water in the washes and the peak flow. By releasing water more slowly than it comes in, the detention basins reduce the peak flows and therefore reduce the danger of flooding downstream. Slowing the flow provides a second critical benefit to desert communities by increasing the contact time the water has in the bottom of the washes and the bottom of the basin, thereby giving runoff a greater chance to infiltrate back into the ground and recharge the aquifer. Increasing the chance for infiltration provides additional recharge to groundwater supplies. This reduces some of the “extra” runoff produced by development and stores it in the aquifer.
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All data reported by the City of Sierra Vista on this website has been provided by the agencies and groups responsible for water management within the Upper San Pedro sub-basin and reviewed by the Upper San Pedro Partnership. All information is consistent with the information provided by those agencies to the USGS for inclusion in the 2008 Section 321 Report to Congress.