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CFr.TK1N q I;, SFnIMFNT CoNTRO1 <br />SC I SILT FI=NCE <br />Limitations • <br />• Maximum drainage area is one-quarter acre per 100 feet of silt fence <br />length; the maximum slope length behind the barrier is 100 feet;; and <br />the maximum gradient behind the barrier is 50 percent (2:1). <br />• Under no circumstances should silt fences be constructed in live <br />streams, swages, or ditches. <br />• On steep slopes, care should be given to placing the fence <br />perpendicular to the general direction of the flow. <br />• Silt fences should not be used in areas where rocky soils will prevent <br />keying in the filter fabric. <br />Materials <br />• The filter fabric shall conform to the requirements described in <br />Section 420 of CDOT's Standard Specifications for Road and Bridge <br />Construction. Minimum height of the filter fabric shall be 36 inches. <br />• The use of joints should be minimized to improve the strength and <br />efficiency of the barrier. <br />• Posts for silt fences shall be metal or hard wood with a minimum <br />length of 42 inches. Wooden posts shall have a minimum diameter or <br />cross section of 1-74 inches. Metal posts shall be "studded tee" or "U" <br />type with a minimum weight of 1.33 lbs/ft, and they shall be <br />protected against corrosion. Metal posts shall. have projections for <br />fastening wire. <br />• When used, wire fence reinforcement for the filter fabric should be a <br />minimum of 36 :inches in height and a minimum of 14 gauge, with a <br />maximum mesh. spacing of 6 inches. <br />Installation <br />• Drive posts vertically into the ground to a minimum depth oi:18 <br />inches, and excavate a trench approximately 6 inches wide and 6 <br />inches deep along the line of posts and upslope from the barrier (see <br />Figure SC 3.2). Not less than the bottom 1 foot of the filter fabric shall <br />be buried into this trench. The trench shall be backfilled and the soil <br />compacted. <br />• When joints are necessary, filter cloth shall be spliced together only at <br />a support post and securely sealed (see Figure SC 3.3 ). <br />• The filter materials shall be fastened securely to metal or wooden <br />posts using wire ties, or to the wood posts with 3l4-inch long #9 he.;Ivy- <br />duty staples. The filter fabric shall not be stapled to existing trees. <br />• Posts shall be spaced a maximum of 10 feet apart. For channel flow <br />applications, the posts shall be spaced a maximum of 3 feet apart. <br />5-49