What options can be used for retention if it is needed on the site?

Retention on a site is a critical practice for managing stormwater runoff, which helps in reducing flooding and controlling pollution. Retention ponds and tanks are specifically designed to collect and hold stormwater runoff. They function by allowing sediments and pollutants to settle out before the water is gradually released or infiltrated over time.

Retention ponds typically feature a deeper basin that stores water and allows for natural processes such as sedimentation and biological treatment to occur. Retention tanks serve a similar purpose but are often used in areas where space is limited, providing a controlled environment for managing stormwater.

While permeable pavement allows for infiltration of rainwater to the underlying soil, it mainly facilitates drainage rather than retention. Trench drains and catch basins help with the initial collection and conveyance of stormwater but are not primarily designed for retention; they are more suited for directing water away from surfaces efficiently. Above-ground storage is a less common approach for retention compared to the more conventional systems of ponds and tanks, which are specifically engineered for this purpose.

Thus, the use of retention ponds and tanks is the most effective and appropriate choice for managing stormwater retention needs on a site.