What should runoff velocities be kept at to effectively manage stormwater on-site?

To effectively manage stormwater on-site, runoff velocities should be kept low to facilitate retention. When runoff velocities are low, water has a greater chance of being absorbed into the ground rather than quickly flowing off the site. This retention allows for better infiltration of water into the soil, which can help recharge groundwater aquifers, reduce the risk of erosion, and limit surface runoff that might carry pollutants into nearby water bodies.

Low velocities are also beneficial in minimizing the potential for erosion of soil particles, which could occur with faster moving water. Additionally, managing water at lower velocities allows for better treatment of stormwater through natural processes, such as sedimentation and filtration, further enhancing water quality before it is discharged.

In contrast, high or variable velocities can lead to increased sediment transport and erosion, which can negate water quality benefits and impact the surrounding environment negatively. Therefore, aiming for low runoff velocities is crucial in stormwater management practices.