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W :er 4 - Best Mana for Erosion and Sediment Control Silt fences composed of a wire support fence and an attached synthetic filter fabric slow the flow rate significantly but have a higher filtering efficiency than burlap. Both woven and non -woven synthetic fabrics are commercially available. The woven fabrics generally display higher strength than the non -woven fabrics. When tested under acid and alkaline water conditions, most of the woven fabrics increase in strength. There are a variety of reactions among the non -woven fabrics. The same is true of testing under extensive ultraviolet radiation. Permeability rates vary regardless of fabric "type. While all of the fabrics demonstrate very, high. filtering efficiencies for sandy sediments, there is considerable variation among both woven and non -woven fabrics when filtering the finer silt and clay particles. Desia�n Catena No formal design is required for many small projects and for minor and incidental applications. For. channel flow applications refer to FOOT Standard Index 102, Chart 1 (Plate 4.06a) for guidance on recommended spacing.' Filter barriers shall have. an expected usable life of 3 months, ons wile a They . applicable in ditch lines, around drop, inlets, and at temporary .. construction changes, the earth contour and runoff chardcferinuous istimand where low or moderate flows (not exceeding 1 cfs) (0.03 rn / sec.} areszpecfed. Silt fences, because they have much lower permeability thanburlap filter barriers, have their app.licability limited to situations in which only sheet or overland flows are expected. They normally cannot filter the volumes of water.generated by channel flows, and many fabrics do not have sufficient structural strength tosupport the weight of water ponded behind the fence line. Their expected usable life is E months. 2. 3. r r✓ go truction Specifications Materials Synthetic filter fabric shall be a pervious sheet of propylene, nylon, polyester, or polyethylene yarii: Synthetic filter fabric shall contain ultraviolet ray inhibitors and stabilizers to provide. a: minimum of 6 months of. expected usable construction life at a temperature range of 0°. F to 120° F` (17C to. 49P Burlap shall be 10 ounces per square. yard (340 gfm) fabric. 3. 4 inch (10 cm}diameter wood, or 1.33 pounds Posts for silt fences shall be either „ per linear foot (2 kg/m) steel with a minimum length of 5 feet (1.5 m). Steel posts shall have projections for fastening wire to them. 4. Stakes for filter barriers shall be 1" x 2" (2.5 x 5 cm) wood (preferred), or equivalent metal with a minimum length of 3 feet (90 cm). 2. to 4-23