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Chapter 4 - Best Management Practices for Erosion and Sediment Control Construction Specifications Materials 1 . Barriers should be a bright color (yellow or "international" orange are recommended) that will attract the attention of nearby boaters . 2 . The curtain fabric must meet the minimum requirements noted in Table 3 .27-A. 3 . Seams in the fabric shall be either vulcanized welded or sewn , and shall develop the full strength of the fabric. 4 . Floatation devices shall be flexible , buoyant units contained in an individual floatation sleeve or collar attached to the curtain . Buoyancy provided by the floatation units shall be sufficient to support the weight of the curtain and maintain *� a freeboard of at least 3 inches (8 cm) above the water surface level . (See Plate 4.45c) 5 . Load lines. must be fabricated into the bottom of all floating turbidity curtains . Type II and Type 111 must have load lines also fabricated into the top of the fabric. The top load line shall consist of woven webbing or vinyl-sheathed steel cable and shall have a break strength in excess of 10 ,000 pounds (4 .5 t) . The supplemental (bottom) load-line shall consist of a chain incorporated into the bottom hem of the curtain of sufficient weight to serve as ballast to hold the curtain in a vertical �. position . Additional anchorage shall be provided as necessary. The load lines shall have suitable connecting devices which develop the full breaking strength for connecting to load lines in adjacent sections (See Plates 4 .45a and 4 .45b which .. portray this orientation) . 6 . External anchors may consist of 2 x 4 inch (5 x 10 cm) or 2-1 /2 inch (6 cm) minimum diameter wooden stakes , or 1 . 33 pounds/linear foot (2 kg/m) steel posts when Type I installation is used ; when Type II or Type III installations are used , bottom anchors should be used . 7 . Bottom anchors must be sufficient to hold the curtain in the same position relative to the bottom of the watercourse without interfering with the action of the curtain . ,. The anchor may dig into the bottom (grappling hook, plow or fluke-type) or may be weighted (mushroom type) and should be attached to a floating anchor buoy via an anchor line . The anchor line would then run from the buoy to the top load line of the curtain . When used with Type III installations , these lines must contain enough slack to allow the buoy and curtain to float freely with tidal changes without pulling the buoy or curtain down and must be checked regularly to make sure they do not become entangled with debris. As previously noted , anchor spacing will vary with current velocity and expected wind and wave action ; manufacturer's recommendations should be followed . See orientation of external anchors and anchor buoys for tidal installation in Plate 4 .45b . i 4- 119