Silt Fences

Finely woven fabric material used to detain water and sediments.

Purpose: Silt fences are installed to trap sediment in swales, small ephemeral drainages, or along hillslopes where other methods cannot be used. They provide temporary sediment storage. Silt fences are also installed to monitor sediment movement as part of effectiveness monitoring.

Relative Effectiveness: Excellent–38% Good–62% Fair –0% Poor–0% (Replies = 8).  Silt fences were considered “good” or “excellent” by interviewees. Most respondents felt they worked well in ephemeral channels, but not all. The size of the watershed above the fence may be important, and silt fences cannot handle debris flows or heavy sediment loads. They work better on gentler slopes, such as swales. Silt fences can be installed on rocky slopes where log erosion barriers would not achieve good ground contact. Sealing the bottom of the fence to the ground well is critical to effectiveness and seems to work best if a trench is dug behind the fence to trap sediment. Silt fences also effectively catch small rocks and ravel on slopes above buildings.

Implementation and Environmental Factors: As noted above, silt fences must be anchored and sealed to the ground to be effective. Sandbags can be used as anchors. Burying the bottom of the fence in a trench is also useful. Rockiness of the soil affects how well the toe of the fence can be buried. When used in ephemeral channels, silt fences must be cleaned out or they can fail and release the stored sediment all at once. They are useful for monitoring sediment movement, and can last several years before failing.