What is the general effectiveness of silt fence barriers?

What is the general effectiveness of silt fence barriers?

• A. They filter water completely and prevent ponding
• B. They do not filter water and are good for ponding
• C. They remove all sediment
• D. They replace other BMPs

Answer: (B)

Silt fences act as a temporary, low-cost sediment-control measure that slows runoff and creates a small backwater behind the fabric. This backwater allows some suspended sediment to settle out before the water continues off the site. Because of this design, they are not a true water filtration device and they do not remove all sediment from the runoff. Their effectiveness is limited to smaller flows; if water levels rise or the barrier is overtopped, sediment can bypass the fence. For this reason, they should be used in combination with other BMPs rather than as the sole control. This is why the statement that they do not filter water and are good for ponding best captures their general role: they mainly pond water to promote sediment deposition rather than providing complete filtration.

Silt fences act as a temporary, low-cost sediment-control measure that slows runoff and creates a small backwater behind the fabric. This backwater allows some suspended sediment to settle out before the water continues off the site. Because of this design, they are not a true water filtration device and they do not remove all sediment from the runoff. Their effectiveness is limited to smaller flows; if water levels rise or the barrier is overtopped, sediment can bypass the fence. For this reason, they should be used in combination with other BMPs rather than as the sole control. This is why the statement that they do not filter water and are good for ponding best captures their general role: they mainly pond water to promote sediment deposition rather than providing complete filtration.