Silt Fences - Fencing to Control Erosion
Silt fence is a low-profile wire-reinforced synthetic fabric barrier designed to slow storm runoff from recently disturbed soil in construction or fire-damaged areas.
The fence is designed to allow water to go through while capturing silt and other small debris.The water approaches the fence in faster-moving concentrated streams, stops and pools behind the fence, seeps through the fence material, and leaves the fence line as a less destructive slow moving sheet of water.
Silt fencing is generally manufactured in heights of two to three feet. It is installed using metal or wood posts that have been sunk into the ground at a depth of 16 to 24 inches, four to six feet apart. Additionally, the bottom four to eight inches of the silt fence is buried beneath the soil line to prevent running water from creating a tunnel under the fence.
Silt fences are manufactured in three grades:
- Grade A silt fence is 36 inches high, and is designed for projects where erosion is a concern for 6 months or more. This is the standard grade for longer term projects such as erosion control after forest fires.
- Grade B silt fence is 22 inches high, and allows the same water throughput as Grade A fencing. This grade us usually used is for projects lasting less than six months, where hillsides are not steep, and where erosion will be quickly controlled with new plant growth, making it ideal for most construction sites.
- Grade C fence, also 36 inches high, is used where the amount or velocity of peak water flow is significantly higher than average. This silt fence allows up to 3 times more water than Grade A fence to pass through in the same time span.
Silt fencing should be periodically inspected for breaks or bulges. Construction regulations often suggest inspection prior to significant storm activity and within 24 hours after such activity. Any single break in the fence negates the effectiveness of the entire fence.