Study of the Effect of Effective Length Variations of Triangular-Shaped Vanes on Erosion and Sedimentation Pattern in a 90° Mild Bend

Application of structures of flow pattern modification is one of the erosion control methods in bends. Triangular vanes are among these structures which provide less scour depth compared to the other techniques such as spur dike. Since little information on erosion and sedimentation pattern around triangular vanes are available, this study was conducted to study the effect of structure effective length variations on erosion and sedimentation pattern. Therefore a triangular vane with different effective lengths (23.3, 17.5, 14 and 10 cm) was tested under different hydraulic conditions (Froude numbers 0.194, 0.214, 0.233 and 0.253). For all experiments, single triangular vane was installed with an angle of 30° relative to the upper bank and outside bend of flume in the 72° location which maximum scour depth is usually occurs. For all tests, flow depth was kept constant equal to 13 cm. At the end of each test bed topography was measured and from that the geometry of scour hole and point bar was measured. The results showed that maximum scour depth has been reduced by reducing of vane effective length. Variations of scour depth for low Froude numbers (0.194 and 0.214) was found to be more than high Froude numbers (0.233 and 0.253). Eroded sediments were transported downstream of vane and accumulated closed to the outer bank. The results showed that, in effective length 10 cm point bar distance from the beginning of vane was almost 0.8 times the effective length of vane for Froude number 0.233 and in effective lengths 14 and 10 cm was respectively, 1 and 2 times the effective length of vane for Froude number 0.253. In addition, minimum point bar distance from the outer bank has been reduced by reducing of vane effective length. For effective lengths of 14 and 10cm the point bar distance from the outer bank was almost 1.5-2 percent width of the flume.