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r <br /> Chapter 4 - Best Management Practices for Erosion and Sediment Control <br /> In addition , a curtain installed in such a manner can "billow up" toward the surface <br /> under the pressure of the moving water, which will result in an effective depth which <br /> is significantly less than the skirt depth . <br /> r <br /> 7 . Turbidity curtains should be located parallel to the direction of flow of a moving body <br /> of water. Turbidity curtains should not be placed across the main flow of a <br /> significant body of moving water. <br /> 8 . When sizing the length of the floating curtain , allow an additional 10 - 20% variance <br /> in the straight line measurements . This will allow for measuring errors, make <br /> installing easier and reduce stress from potential wave action during high winds. <br /> 9 . An attempt should be made to avoid an excessive number of joints in the curtain ; a <br /> minimum continuous span of 50 feet (15 m) between joints is a good 'Yule of <br /> thumb ." <br /> r <br /> 10 . For stability reasons , a maximum span of 100 feet (30 m) between anchor or stake <br /> locations is also a good rule to follow. <br /> i <br /> 11 . The ends of the curtain , both floating upper and weighted lower, should extend well <br /> up into the shoreline, especially if high water conditions are expected . The ends <br /> r should be secured firmly to the shoreline to fully enclose the area where sediment <br /> may enter the water. <br /> 12 . When there is a specific need to extend the curtain to the bottom of the watercourse <br /> in tidal or moving water conditions , a heavy woven pervious filter fabric may be <br /> substituted for the normally recommended impervious geotextile . This creates a <br /> .. "flow-through" medium which significantly reduces the pressure on the curtain and <br /> will help to keep it in the same relative location and shape during the rise and fall <br /> of tidal waters . <br /> 13 . Typical alignments of turbidity curtains can be seen in Plate 4 .45c. The number <br /> and spacing of external anchors may vary depending on current velocities and <br /> i potential wind and wave action ; manufacturer's recommendations should be <br /> followed . <br /> i 14. Be certain that the type , location , and installation of the barrier is as shown on the <br /> approved plan and permit. Additional permits may be required in navigable <br /> waterways, especially when the barrier creates an obstruction . <br /> r <br /> i <br /> i <br /> 4- 117 <br /> r <br />