EFFECT OF SUBMERGED VANE SHAPE ON LOCAL SCOUR AND SEDIMENTATION PATTERNS IN ALLUVIAL CHANNELS

The technique of submerged vanes (Iowa vanes) is a new and efficient method for sediment management in rivers. This method has positive environmental effects. The performance and efficiency of a submerged vane is related to its shape. In the past, using of simple rectangular vanes was common. Recently some studies are in progress to reduce the vanes dimension and optimize their shape. The ultimate goal is to lower the costs and improve the vanes performance by reduction of local scour that occurs around the submerged vanes. The present paper attempts to address these issues. In the present study, physical hydraulic model testing was performed to investigate four shapes of vanes: a simple rectangular vane, and three vanes that are beveled at leading edge of θ=30°, 45°, and 60° with respect to the base, respectively. The experiments were carried out at four Froude numbers of Fr = 0.14, 0.16, 0.18, and 0.20. Clear water scour occured at Fr = 0.14 and 0.16 and live bed scour arised at Fr = 0.18 and 0.20. Results determine the performance and effectiveness of the vanes based on local scour occurred around the vanes and sedimentation pattern at downstream of the vanes. Results showed that maximum decrease of the depth of scour hole, for θ =60° and respect to the baseline rectangular vane, was 33%, 49%, 43% and 28% at Fr = 0.14, 0.16, 0.18 and 0.20 respectively. The maximum reduction of scour depth at leading edge of the vanes was observed at θ =60°. The estimated decreases were 41%, 48%, and 61% at Fr of 0.14, 0.16 and 0.18 respectively. At Fr = 0.2 the scour depth at the leading edge of the vane reduced to zero.