What is a Silt Barrier?

Alan Rankin

A silt barrier, sometimes called a silt fence, is a device used in construction, landscaping, and earth-moving projects. The function of the barrier is to prevent silt, soil, and pollutants from draining off the site and into nearby sewers or bodies of water. Silt is the name for tiny particles of soil that are carried away by water, a process called erosion. A natural process, erosion can be increased when vegetation is disturbed or removed. Although it is called a silt barrier, the device is designed to capture other substances as well while allowing water to flow through.

A silt barrier may be installed to prevent soil disturbance of an area.
A silt barrier may be installed to prevent soil disturbance of an area.

Erosion occurs when rain or other water flows over soil, bearing away the small particles called silt. Vegetation has a natural diminishing effect on erosion, keeping most soil in place with roots and ground cover. Human construction and landscaping projects often remove this vegetation and its erosion protection. A heavy rain can carry away large amounts of soil from a construction site, along with chemicals, metal fragments, and other pollutants. A silt barrier is designed to impede this process when properly installed and used.

Construction companies may install silt barriers before starting work on a site.
Construction companies may install silt barriers before starting work on a site.

A silt barrier is made of a porous fabric called a geotextile. The pores in the fabric are small enough to filter out most solid particles from any water escaping the site. The barrier is erected along a likely erosion path such as a hillside. The lower edge is buried well below the surface of the ground and then reinforced so it will not be dislodged by heavy water flows; upright stakes at regular intervals keep the barrier erect. Silt and sediment gather against the barrier, where they can be processed back into the site’s land when the project is finished.

Specialized silt fences are used in areas where heavy runoff is expected. Another kind of silt barrier is designed for use in underwater construction. This barrier is taller than the depth of the water, effectively creating a wall to capture any sediment dislodged by the construction. It is weighted with chains at the bottom to prevent it from moving in the current. Specialists often supervise the installation of these silt barriers to customize them to the requirements of the site.

Regulatory agencies such as the U.S. Environmental Protection Agency (EPA) require the use of silt barriers to preserve the integrity of construction sites and nearby waterways. The EPA warns that a silt barrier must be carefully maintained to serve its purpose. The fragile fabric can often be damaged by construction equipment and improper care. Some silt fences must be moved several times during a project and may not be re-installed properly in the rush of activity. These factors can reduce a silt barrier’s effectiveness, with damaging long-term consequences.

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