2008-009 (6) - Laserfiche WebLink

Home Browse Search

r. nt Practices for Erosion and Sediment Control Chapter 4 - Best Mara eme Silt fences composed of a wire support fence and an attached synthetic filter fabric slaw 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. fettering efficiencies for sandy sediments , there is considerable variation among both woven and non-woven fabrics when filtering the finer silt and clay particles . w Desia�riter�a 1 , No formal design is required for many small projects and for minor and incidental applications . Forchannel flow applications refer to FOOT Standard Index 102 , Chart 1 (plate 4. 06a) for guidance on recommended spacing, 2 . Filter barriers shall have. an expected usable life of 3 months .oans They where .applicable in ditch lines, around drop , inlets , and at temporary .. construction changes,the earth contour and runoff characterinuous istics :and where low or moderate flows (not exceeding 1 cfs) (0 .03 rn / sec. are szpecfed. 3. Silt fences, because they have much lower permeability thanburlap filter barriers , r have their applicability 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 6 months . gotruction Specifications Materials y , Synthetic filter fabric shall be a pervious sheet of propylene, nylon, polyester, or polyethylene yarri . Synthetic filter fabric shall contain ultraviolet ray inhibitors and -� stabilizers to provide. a: minimum 6 months of. expected usable construction life at a temperature range of 0°. F to 120° F` (17d to 49.. r, 2. Burlap shall be 10 ounces per square. yard (340 gfm) fabric. 3 . Posts for silt fences shall be either 4 inch (10 cm) diameter wood , or 1 . 33 pounds „ 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). • 4-23