Paper Title
Effects of Groynes 'S Widthes to Control Sedimentation in A 90 Degree Arch

One of the effective and cost-effective ways to protect the banks of rivers in the places of arches is to use groynes. In the present research, the effect of a series of non-submersible groynes with an angle of placement (90° vertical groynes), relative to the outer wall of the arch with two lengths of 15% and 25% of the channel width, on the distribution of average velocity and shear stress in the mild 90 degree arch with a ratio of 𝐑/𝐁=4, width 0.7 meters and water depth 0.14 meters. The results of the study showed that the presence of a series of groynes causes the uniformity of the upstream speed and the transfer of the high-speed area from the vicinity of the outer wall to the middle of the channel to the inner wall. The bed shear stress is increased due to the presence of groynes and the increase in the length of groynes increases it to about 1.5 times the shear stress upstream of the arch, but it does not have much effect on the location of the occurrence of shear stress. Keywords - Rectangular groyne, flow pattern, secondary flow, 90 degree arc, Numerical model.