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BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

BEsT MANAGEMENT PRACTICEs HANDbooK - Tahoe BMP

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weeks); longer durations or extensive projects may require a double curtaindeployment. 56Table 8-18 details some of the common advantages and disadvantages associatedwith turbidity curtains.Table 8-18: Advantages and Disadvantages of using Turbidity CurtainsADVANTAGE• Are reasonably adequate at containingsediment and turbid water within thedisturbed area.• Can effectively localize the turbidity plumesand help reduce visual impacts.• Promotes the settling of fine sedimentswhich in turn lets some leached nutrientsre-adsorb and re-sequester.DISADVANTAGE• Susceptible to weather events and may fail ifleft exposed and unprotected.• Wind induced wave action must be minimalor will have limited effectiveness.• Not designed for long-term projects.Turbidity curtains subject to hydraulic turbulence due to the removal oraddition of water may be more prone to fail. If possible, direct hydraulic headtowards the operational area and away from the containment technology.Hydraulic head directed toward a curtained area will cause stress to itsanchoring and may lift or dislodge the weighted curtain bottom and impair itseffectiveness. It may prudent or necessary to divert turbulent flows away froma curtained perimeter to avoid any compromise to turbidity containment. 578.10.3 DESIGN CONSIDERATIONS AND PLANNINGSeveral variables determine the effectiveness of turbidity barriers, including thetype of dredging activity occurring, the quantity and type of material beingretained by the barrier (e.g. contaminated fine sediment); the materialcondition and construction of the barrier; the configuration of the areaenclosed by the barrier; and the method of deployment and attachment.Positioning of the turbidity barrier to capture and contain turbid water iscritical to the success of this control measure. Barriers must remain structurallysound and securely in place and operational throughout the dredging orconstruction activities. The turbidity curtain material must be totallyimpermeable when the construction or dredging activities are expected toresult in water quality impacts that exceed surface discharge standards for anextended duration of time.Water quality is usually most degraded towards the bottom of the watercolumn. 58 Turbidity barrier bottoms must be sufficiently anchored with56<strong>Tahoe</strong> Research Group, 1996, C.R. Goldman, John E. Reuter, Scott H. Hackley, Final Report,Impacts of Marina Dredging on Lake <strong>Tahoe</strong> Water Quality57USACE, 1995, Engineer Manual EM 1110-2-1810, Engineering and Design: Coastal Geology58USACE, 1995, Engineer Manual EM 1110-2-1810, Engineering and Design: Coastal GeologyCHAPTER 8: Shorezone Protective Structures and <strong>BMP</strong>sTRPA <strong>BMP</strong> Handbook8.10 Turbidity Curtains 2012Page 8-66

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