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. , '+. United States Department of Agritultu re 0 NRCSConservationDService COLORADO FACT SHEET SILT FENCE What is a Silt This is a temporary barrier made of woven wire and fabric filter cloth Fence? (Geotextile) that is used to catch sediment-laden runoff from small areas of disturbed soil such as following a fire. There are many brands of silt fence available that lack the woven wire support and they are not recommended for the uses descibed below. When is a Silt Silt fences are used for specific situations. Major considerations are Fence Used? slope, slope length, and the amount of drainage area from which the fence will catch runoff. Here are some design considerations: Slope Steepness Maximum Slope Length 2:1 (50%) 50 feet 3:1 (33%) 75 feet 4:1 (25%) 125 feet 5:1 (20%) 175 feet < 5:1 (<20%) 200 feet Drainage Area Limitation. The area that contributes runoff to be caught by the silt fence should not be greater than 1/2 acre for 100 feet offence. Location Limitation. Silt fences should be installed on the contour of a slope. Silt fences should not be installed across drainage ways, swales, gullies, ditches or other areas of concentrated water flow. What Materials are Fence Posts. Posts should be at least 36 inches long. Wood posts Needed? should be of hardwood with a minimum cross sectional area of 3 inches. Steel posts should be standard "T" or "U" section and should weigh no less than 1 pound per linear foot. Wire. Wire fence should be at least 14 gage with openings no larger than 6 inches by 6 inches. Geotextile Fabric. The fabric should have the following minimum material properties Geotextile Property Minimum Value Test Method Grab Tensile Strength 90 lbs. ASTM D1682 Elongation at Failure 50 % ASTM D1682 Mullen Burst Strength 190 psi. ASTM D3786 Puncture Strength 40 lbs. ASTM D751 (mad) Equivalent Opening Size 40 - 80 US Std Sieve Sizes Ultraviolet Radiation Stability 90 ASTM G26 The NaNral Resources Conservation Service Drovides leadership m a partnership effort to help People conserve, maintain, and improve our natural resources and environment.