2007-012A - Laserfiche WebLink

Home Browse Search

r Chapter 4 - Best Management Practices for Erosion and Sediment Control Installation In the calm water of lakes or ponds (Type I installation) it is usually sufficient to merely set the curtain end stakes or anchor points (using anchor buoys if bottom anchors are employed) , then tow the curtain in the furled condition out and attach it r to these stakes or anchor points . Following this , any additional stakes or buoyed anchors required to maintain the desired location of the curtain may be set and these anchor points made fast to the curtain . Only then , the furling lines should be r cut to let the curtain skirt drop . 2 . In rivers or in other moving water (Type II and Type III installations) it is important to set all the curtain anchor points. Care must be taken to ensure that anchor points ' are of sufficient holding power to retain the curtain under the expected current conditions , before putting the furled curtain into the water. Anchor buoys should be employed on all anchors to prevent the current from submerging the flotation at the ' anchor points . If the moving water into which the curtain is being installed is tidal and will subject the curtain to currents in both directions as the tide changes, it is important to provide anchors on both sides of the curtain for two reasons: r a) Curtain movement will be minimized during tidal current reversals . b) The curtain will not overrun the anchors pull them out when the tide reverses. When the anchors are secure , the furled curtain should be secured to the upstream anchor point and then sequentially attached to each next downstream anchor point until the entire curtain is in position . At this point, and before unfurling , the 'lay" of the curtain should be assessed and any necessary adjustments made to the anchors . Finally, when the location is ascertained to be as desired , the furling lines should be cut to allow the skirt to drop. 3 . Always attach anchor lines to the flotation device not to the bottom of the curtain . The anchoring line attached to the floatation device on the downstream side will provide support for the curtain . Attaching the anchors to the bottom of the curtain could cause premature failure of the curtain due to the stresses imparted on the middle section of the curtain . 4 . There is an exception to the rule that turbidity curtains should not be installed across channel flows ; it occurs when there is a danger of creating a silt buildup in the middle of a watercourse , thereby blocking access or creating a sand bar. Curtains have been used effectively in large areas of moving water by forming a very long-sided , sharp "V" to deflect clean water around a work site, confine a large part r of the silt-laden water to the work area inside the "V" and direct much of the silt toward the shoreline . Care must be taken , however, not to install the curtain perpendicular to the water current. 5 . See Plate 4 .45c for typical installation layouts . r 4-121 r