What is a primary function that a silt fence cannot achieve?

A silt fence is commonly used in construction and land disturbance sites as a sediment control measure. Its primary functions include controlling sediment movement, providing a barrier to pollutants, and filtering runoff. However, controlling water velocity is not one of its effective functions.

While a silt fence can slow down water and promote sedimentation through its fabric, it is primarily designed to intercept sediment-laden runoff rather than manipulate water velocity effectively. When water flows over a silt fence, it may still carry some sediment with it, especially if the flow is too rapid or exceeds the design limits of the fence. In contrast, best management practices for controlling water velocity involve broader techniques such as properly designed check dams, outlet structures, or vegetative swales that can address the dynamics of surface water movement more effectively.

Therefore, recognizing that a silt fence is not intended to serve as a primary tool for managing water velocity clarifies why this option is the correct response.