2007-012A - Laserfiche WebLink

Home Browse Search

Chapter 4 - Best Management Practices for Erosion and Sediment Control 4.45 FLOATING TURBIDITY BARRIER Definition A floating geotextile material which minimizes sediment transport from a disturbed area adjacent to or within a body of water. Purpose To provide sedimentation protection for a watercourse from up-slope land disturbance where conventional erosion and sediment controls cannot be used , or from dredging or filling within the watercourse. Conditions Where Practice Applies Applicable to non-tidal and tidal watercourses where intrusion into the watercourse by construction activities has been permitted and subsequent sediment movement is _ unavoidable . Planning Considerations Soil loss into a watercourse results in long-term suspension of sediment. In time , the suspended sediment may travel large distances and affect widespread areas . A turbidity curtain is designed to deflect and contain sediment within a limited area and provide enough residence time so that soil particles will fall out of suspension and not travel to other areas . Turbidity curtain types must be selected based on the flow conditions within the water body, whether it be a flowing channel , lake , pond , or a tidal watercourse . The specifications contained within this practice pertain to minimal and moderate flow conditions where the velocity of flow may reach 5 feet (1 .5 m) per second (or a current of approximately 3 knots). For situations where there are greater flow velocities or currents , a qualified engineer and product manufacturer should be consulted . Consideration must also be given to the direction of water movement in channel flow situations . Turbidity curtains are not designed to act as water impoundment dams and cannot be expected to stop the flow of a significant volume of water. They are designed and installed to trap sediment, not to halt the movement of water itself. Inmost situations , turbidity curtains should not be installed across channel flows . In tidal or moving water conditions , provisions must be made to allow the volume of water contained within the curtain to change . Since the bottom of the curtain is weighted and external anchors are frequently added , the volume of water contained within the curtain will be much greater at high tide verses low tide and measures must be taken to prevent the curtain from submerging . In addition to allowing slack in the curtain to rise and fall , water must be allowed to flow through the curtain if the curtain is to remain in roughly the same place and maintain the same shape. Normally, this is achieved by constructing part of the curtain from a heavy woven filter fabric. The fabric allows the water to pass through the 4-115