Silt Fencing

A Silt Fence is a temporary silt control device that helps to prevent the loss of silts from a site during rain, or other run-off events. Silt Fences are temporary silt control devices that are designed to prevent the release of silt from a construction site. Silt fences prevent silt contamination of sensitive areas such as neighboring properties, streams, and sewer catch basins.

 

A properly installed and maintained silt fence will collect silts before they can cause contamination requiring expensive clean up. Silt fences create a puddle behind the fence that acts as a "stilling basin" allowing silts to settle. Silt Fences are most often used on construction sites where the soil has been stripped of natural vegetation. Silt fences are manufactured with a woven geotextile fabric on wooden or steel posts. The fabric is attached to the post with staples or other suitable fasteners and then packaged for shipment. Placement of stakes varies with the region and the specifications of different jurisdictions, however spacing of 8 ft and 10 ft are common. Typical silt fences are 3 ft high with 4 ft stakes for anchoring.

 

Silt fences help to keep silts out of catch basins, streams and waterways, off of streets, and out of neighboring property. By preventing the loss of silt and sediment from the construction site to these sensitive areas cleanup costs are eliminated.

 

Silt fences must be installed properly to work. A small trench must be dug in the soil to anchor the bottom end of the fabric. The anchor trench is usually about 150 mm deep by 150 mm wide (6 inches by 6 inches). If the fabric is not anchored then the water can flow under the fence and the fence will not remove silts.

 

The bottom of the fabric is placed in this trench on the upstream side of the fence and then carefully backfilled. Adjacent lengths of silt fence are rolled together around the end posts. Silt Fences must also be periodically cleaned to remove collected silt and sediment. If silts and sediment are allowed to accumulate then the fence may be overwhelmed by the weight which can lead to failure of the fence. Most silt fence failures are caused by lack of maintenance. After each period of heavy run-off, silts will have accumulated behind the fence. If the accumulation of silt becomes too deep the weight will overwhelm the fence and allow the silts to escape.

 

To prevent this failure the collected silts should be removed from the back of the fence periodically. The fence fabric should also be rinsed of silts. Removing silt and washing down the fabric prevent silt accumulations from overwhelming the fence.