, Australia Detention basins are storm water
best management practices 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
urban 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
culverts 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. Research has shown that detention basins built with real-time control of the outflow from the basin are significantly more effective at retaining
total suspended solids and associated contaminants, such as
heavy metals, when compared to basins without control. ==Extended detention basin==