Silt fences are temporary barriers used at sites where the soil is likely to be disturbed by construction activities. They allow drainage while containing sediment. They are designed to protect nearby streams, creeks and other bodies of water from sediment contamination in stormwater runoff. They remain in place until a construction project is complete and the disturbed soil can be stabilized. They are generally made with porous fabric and metal or wood anchoring posts. Better quality silt fencing fabric is made from woven material with a high tensile strength and proper permeability.
Federal regulations, chiefly the Clean Water Act, require almost all construction sites engaged in activities that disturb one acre or more of soil to employ a permitted plan to deal with their stormwater runoff. Silt fencing is often an important component of such a plan. The Environmental Protection Agency (EPA) provides free guidelines for both developing a stormwater prevention plan and properly installing a silt fence. A silt fence is intended to control sheet or overland discharge. They are inappropriate in areas where water flow is concentrated.
Most commonly, silt fencing surrounds the perimeter of a construction project. It is rarely necessary to surround the entire site. The fencing should be placed on the downslope edge of the project, but not running up or down the slope of a hill. The idea is to create a ponding area to retain sediment. Long runs of fencing are problematic as water may pool, and then overflow containment, at the lowest point of a long segment. Using several shorter, j-hook segments will effectively contain runoff.Silt fencing can also be used within a construction site. It can be used for containment around soil stockpiles and temporary spoil areas. Smaller cleared areas might also require silt fencing. Some local governments require a double row of silt fencing if the site drains directly into a creek, pond, wetland, or similar body of water.
Silt fencing can be effectively utilized along (but not in or across) streams and small channels. This is especially important for culvert placement and removal projects. A streamside barrier can also act as a second line of defense for a particularly vulnerable stream or creek. Many municipalities and counties require silt fencing along creeks and channels if they are within 30 feet of a road construction project.
Silt fencing is also used in a severe storm and/or flood events. Cheap and relatively easy to quickly put in place, silt fencing can be used as a stop-gap measure when flood waters threaten to overflow a containment channel or sediment basin. It can also be effective when sediment-rich water begins to leak beneath an established silt berm.
Keeping sediment-filled flood waters from entering waterways is essential. On the short term, sediment can clog storm drains and cause additional flooding. Sediment filled waterways prevent the growth of natural vegetation and encourage the growth of toxic algae blooms. Sediment degrades the habitat of fish and other marine creatures. Simple containment measures, like silt fencing, can greatly reduce these negative outcomes.