What Is a Detention Basin?
A detention basin is a critical disaster prevention facility designed to offset the reduced water retention capacity caused by urban development. As cities expand and natural land is developed, the ground’s ability to absorb rainwater diminishes. This leads to increased runoff into rivers and urban infrastructure, potentially causing human casualties and property damage during heavy rainfall. Detention basins, often constructed underground, serve to temporarily store this excess rainwater, thereby controlling runoff and mitigating flood risks.
Beyond basic detention basins, there are also facilities specifically designed for river flow control, such as recreational and regulating reservoirs. These reservoirs manage river levels by allowing overflow into the basin when river waters rise, with overflow levees built lower than the surrounding land.
Uses of Detention Basins
Historically, the abundance of forests and fields meant sufficient natural water retention. However, with increased urbanization and land conversion to residential areas, the direct runoff of rainwater into rivers has become more prevalent. Efforts to contain this runoff through concrete-lined rivers and channels have their limitations, as rivers can only handle a certain volume of water. Expanding river widths in urban areas is often impractical due to space constraints.
Detention basins, which can be constructed even in urban settings, offer a solution. They allow for multifunctional land use, such as building recreational facilities like baseball fields over them. Known for their flood control capabilities, these basins play a vital role in urban flood management.
Principles of Detention Basins
Detention basins come in various types, each suited to different urban environments and requirements.
- Moat: This involves excavating the ground surface to create a basin for rainwater storage. Overflow levees are designed to release excess water, helping to control flooding. The typical depth ranges from 1 to 5 meters.
- Underground Box: This type features a subterranean box-like structure for temporary water storage. Similar to the moat in its basic design, the box basin includes storage sections and overflow dikes, but its presence is less visible on the ground surface. The storage depth can range from 10 to 30 meters.
- Tunnel: Comprising intake and drainage stands, this type utilizes vertical shafts resembling tunnels for capturing and storing rainwater underground, followed by gradual discharge. These tunnels typically have diameters of 7 to 13 meters.
In mountainous regions, other forms of regulating reservoirs, like dams and pool basins, are often employed.