Silt Fence

Silt Fence, sometimes (misleadingly) called a “filter fence,” is a temporary sediment control device used on construction sites to protect water quality in nearby streams, rivers, lakes and seas from sediment in stormwater runoff. Silt fences are widely used on construction sites throughout North America due to their low cost and simple design.

Design and installation
Silt fences are perimeter controls, typically used in combination with sediment basins and sediment traps, as well as erosion controls, which are designed to retain sediment in place where soil is being disturbed by construction processes.

Our line of silt fences typically consist of a synthetic filter fabric stretched between a series of wooden or metal fence stakes along a horizontal contour level. The stakes are installed on the downhill side of the fence, and the bottom edge of the fabric is trenched into the soil and backfilled on the uphill side. The stormwater slowly passes through the fence while depositing its sediments on the uphill side of the fence. The fence is not designed to concentrate or channel stormwater. The fence is installed on a site before soil disturbance begins down-slope from the disturbance area.

Sediment is captured by silt fences primarily through ponding of water and settling, rather than filtration by the fabric. Sand and silt tends to clog the fabric, and then the sediments settle in the temporary pond.

Effectiveness
Silt fence fabrics tested in laboratory settings have shown to be effective at trapping sediment particles. Silt fences may perform poorly for a variety of reasons, including improper location (e.g. placing fence in an area with concentrated stormwater flows), improper installation (e.g. failure to adequately embed and backfill the lower edge of fabric in the soil) and lack of maintenance. The fabric may become damaged with holes and tears if construction materials are stored next to or on top of the fence. During various phases of construction at a site, a silt fence may be removed relocated and reinstalled multiple times. It may be difficult to maintain effectiveness of a silt fence under such operating conditions. Location of fences in areas with high flows may lead to fence failures. Some state agencies recommend an installation technique called “static slicing” as an improved method for ensuring effectiveness and longevity of a silt fence system on a construction site.

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