Efficiency of Hanging Silt Curtains in Crossflow

Abstract

When dredging in sensitive environments, efforts have to be made to limit the free dispersal of suspended fine sediment from the dredging spill. The use of hanging silt curtains as an environmental mitigation measure is especially widespread. Despite frequent application, their ability to reduce turbidity levels through vertical diversion of sediment-laden currents remains the subject of debate. This paper addresses a series of laboratory measurements and numerical model simulations to determine the efficiency of hanging silt curtains, defining a new efficiency parameter. The model was validated against the laboratory experiments. Model simulations focusing on vertical diversion of the sediment-laden current suggest that hanging silt curtains do not have a favorable influence on the settling of suspended sediment when applied in crossflow. The diversion of currents underneath the curtain causes flow separation and intense turbulent mixing, which counteracts settling of suspended sediment particles. The results imply that the widespread application of hanging silt curtains should be reconsidered from a physical point of view.