What type of runoff management structure holds water temporarily?

The correct choice is a detention basin, as it is specifically designed to temporarily hold runoff water and gradually release it at a controlled rate. This type of structure plays a critical role in managing stormwater by capturing excess precipitation and reducing the risk of flooding downstream. The primary function of a detention basin is to mitigate peak flow rates during and after a storm event, thus helping to manage the overall volume of water that enters drainage systems.

Detention basins generally have a defined outlet structure that allows for the controlled release of water, usually after the storm has passed, which contributes to reducing erosion and water quality impacts downstream. They typically are dry after significant rainfall, as the majority of the stored water is drained out as designed.

In contrast, a retention basin is designed to hold a certain water level permanently and is intended for long-term storage, which allows for the natural treatment of water over time. A storage tank holds water but does not typically deal with surface runoff management, while wetlands provide a more natural form of water treatment and habitat but are not explicitly designed for the temporary holding of stormwater runoff in a controlled manner like a detention basin.