What is the key purpose of a detention basin?

The primary purpose of a detention basin is to store runoff temporarily. This temporary storage helps to manage the flow of stormwater and reduce the peak discharge rates that occur during heavy rainfall events. By holding back excess water, detention basins allow for a controlled release into the downstream drainage system, which helps to mitigate flooding, erosion, and water quality issues in receiving waters.

While filtering pollutants is important in stormwater management, this is not the primary function of a detention basin. Additional features, such as vegetative swales or sediment traps, are often integrated to enhance pollutant removal. Similarly, while increasing evaporation rates can be a secondary effect of a detention basin, it is not its main purpose. Recreational space is often considered an ancillary benefit but does not define the basin's essential function in stormwater management. Thus, the correct answer focuses on the basin's role in temporarily storing runoff.