What refers to runoff that is temporarily held to manage flow rates and enhance water quality?

The term that refers to runoff that is temporarily held to manage flow rates and enhance water quality is detention. Detention systems capture stormwater runoff and store it for a short period, allowing for controlled release. This process helps to reduce peak flow rates during rainfall events, which can prevent downstream flooding and erosion. Additionally, by holding the water temporarily, detention facilities can enhance water quality through sedimentation and biological processes, ultimately allowing cleaner water to be discharged into receiving bodies.

In contrast, retention refers to practices that store water permanently, maintaining a pool of water year-round, which is different from the temporary holding implied in the question. Conveyance pertains to the transportation of water through systems such as pipes and channels rather than holding it. Storage could be used in a more general sense, but it does not specify the temporary aspect that is crucial for effective stormwater management.