A detention basin is normally dry, constructed to store water temporarily to attenuate flows. This permits settlement of coarse solids within the drainage system. Outlets are normally designed to empty over a 24-hour period and the maximum depth of water should not exceed 3m, only occuring for the design storm.

As these features are normally dry, they may be used for other purposes when not required for drainage. A detention basin may also allow infiltration of water to the ground. Where further conveyance of flow is required, the base of the detention basin should be designed to drain freely to ensure that standing water is not left on the basin floor.