What mechanism do detention systems mainly employ?

Detention systems are designed primarily to manage stormwater by temporarily holding it before gradually releasing it into the environment. This mechanism helps control the rate and volume of runoff, reducing the potential for flooding and erosion downstream. By capturing excess stormwater during heavy rains and releasing it at a controlled rate, detention systems provide critical time for sedimentation and filtration processes to occur, which improves water quality.

The other options suggest actions that do not align with the primary function of detention systems. For instance, containing water permanently would be characteristic of a retention system rather than a detention system, as retention systems are designed to keep water in place indefinitely. Absorbing water focuses on the infiltration aspect, which is not the main mechanism of detention systems that explicitly hold and release water. Lastly, evaporating water does not encapsulate the intended function, which is more about management through storage rather than loss via evaporation. Thus, the emphasis on holding water and then releasing it efficiently captures the essence of what detention systems do.