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BMP C233: Silt Fence <br /> Purpose Use of a silt fence reduces the transport of coarse sediment from a <br /> construction site by providing a temporary physical barrier to sediment <br /> and reducing the runoff velocities of overland flow. See Figure 4.19 for <br /> details on silt fence construction. <br /> Conditions of Use Silt fence may be used downslope of all disturbed areas. <br /> • Silt fence is not intended to treat concentrated flows, nor is it intended <br /> to treat substantial amounts of overland flow. Any concentrated flows <br /> must be conveyed through the drainage system to a sediment pond. <br /> The only circumstance in which overland flow can be treated solely by <br /> a silt fence, rather than by a sediment pond, is when the area draining <br /> to the fence is one acre or less and flow rates are less than 0.5 cfs. <br /> • Silt fences should not be constructed in streams or used in V-shaped <br /> ditches. They are not an adequate method of silt control for anything <br /> deeper than sheet or overland flow. <br /> Joints in filter fabric shall be spliced at <br /> posts.Use staples,wire rings or 2"x2"by 14 Ga.wire or <br /> equivalent to attach fabric to posts equivalent,if standard <br /> strength fabric used <br /> Filter fabric <br /> E <br /> N <br /> I-1 Ill n l-n i=1 i <br /> — 7'1-- �/ ... i <br /> 6'max T -u_ <br /> Minimum 4"x4"trench / -"i=ili <br /> Backfill trench with native soil <br /> Post spacing may be increased or 3/4"-1.5"washed gravel <br /> to 8'if wire backing is used <br /> 2"x2"wood posts,steel fence <br /> posts,or equivalent <br /> Figure 4.19—Silt Fence <br /> Design and • Drainage area of 1 acre or less or in combination with sediment basin <br /> Installation in a larger site. <br /> Specifications <br /> • Maximum slope steepness (normal (perpendicular) to fence line) 1:1. <br /> • Maximum sheet or overland flow path length to the fence of 100 feet. <br /> • No flows greater than 0.5 cfs. <br /> • The geotextile used shall meet the following standards. All geotextile <br /> properties listed below are minimum average roll values (i.e.,the test <br /> result for any sampled roll in a lot shall meet or exceed the values <br /> shown in Table 4.10): <br /> 4-94 Volume II— Construction Stormwater Pollution Prevention February 2005 <br />