Which terrain should silt fences never be placed on?

Which terrain should silt fences never be placed on?

• A. A well-vegetated hillside
• B. Flat ground
• C. Low slope areas
• D. A Hill

Answer: (D)

Silt fences are placed across a slope to slow sheet runoff and allow sediment to settle behind the barrier; they work best on level ground or gentle slopes where water velocity remains low and flow can be intercepted effectively. On a hill, runoff becomes concentrated and moves quickly downslope, which can overwhelm and fail the fence—causing overtopping, trench erosion, or sediment bypass—so it’s not a reliable placement there. The other terrains listed are more workable for silt fences because they minimize the risk of rapid, concentrated flow, whereas a hill creates conditions that defeat the device.

Silt fences are placed across a slope to slow sheet runoff and allow sediment to settle behind the barrier; they work best on level ground or gentle slopes where water velocity remains low and flow can be intercepted effectively. On a hill, runoff becomes concentrated and moves quickly downslope, which can overwhelm and fail the fence—causing overtopping, trench erosion, or sediment bypass—so it’s not a reliable placement there. The other terrains listed are more workable for silt fences because they minimize the risk of rapid, concentrated flow, whereas a hill creates conditions that defeat the device.