Silt fence

Silt Fence is a temporary sediment control device used in construction sites to protect water quality in nearby streams, rivers, lakes, and seas from sediment (loose soil) in stormwater runoff. Silt fences are widely used on construction sites in North America and elsewhere, due to their low cost and simple design. However, their effectiveness in controlling sediment can vary significantly, depending on the quality of their installation and maintenance.

Design and Function

A silt fence is essentially a porous barrier made of synthetic fabric, such as woven polypropylene, stretched between a series of wooden or metal posts driven into the ground. The fabric has the property of allowing water to pass through while trapping sediment. The trapped sediment settles out from the water, allowing cleaner water to flow out of the fenced area. Silt fences are designed to intercept and slow the flow of sediment-laden runoff, promoting sedimentation behind the fence.

Installation

Proper installation is critical for the effective functioning of a silt fence. The fence should be installed on a level contour to maximize runoff interception. The bottom edge of the fabric should be buried in the ground to prevent undercutting by runoff. Overlapping sections of the fence should face upstream to prevent water from flowing through the gaps. Regular maintenance is required to repair any damage and remove sediment accumulations.

Applications

Silt fences are primarily used in construction sites to prevent sediment from leaving the site and entering natural water bodies or storm drainage systems. They are also used around temporary stockpiles and other areas prone to erosion. While silt fences are effective for trapping finer particles, they are not suitable for controlling large water flows or for use as a stabilization measure on steep slopes without additional support.

Limitations

The effectiveness of silt fences can be limited by improper installation, lack of maintenance, and the nature of the site. They are not designed to withstand large volumes of water or heavy sediment loads. In such cases, additional or alternative erosion and sediment control measures may be necessary.

Environmental Impact

Silt fences can have a positive impact on the environment by preventing sediment pollution in water bodies, which can harm aquatic life and degrade water quality. However, the use of synthetic materials raises concerns about the environmental footprint of these barriers, particularly regarding the disposal of used fabric.

Regulations

In many jurisdictions, the use of silt fences and other sediment control measures is regulated by environmental protection agencies. Construction sites may be required to implement silt fences as part of their stormwater pollution prevention plans (SWPPP).

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