Experimental Study on Effects of Permeability and Spur Dike Series Length on Scour-Hole Dimensions in a 90° mild bend under non-submerged conditions

River changes happen due to the periodic erosion and sedimentation along river bed, destruction and widening of river banks, movement of the meandering pattern and flow direction, changing of river form (braided, sinusoidal, and straight), and shortcut or diversion of river path. One of the common hydraulic structures for erosion controlling in river bend is spur dike. Ezzeldin et al (2007) conducted experiments on a permeable spur dike to investigate the effect of the fluctuation ratio and the angle of attack on the scour hole dimensions. Based on the obtained results, for the same flow conditions and the degree of tightness, a 30-degree angle has been found to have a good effect on scour depth reduction in the nose and controlling coastal erosion. Nasrollahi et al (2008) examined the experimental investigation on the scouring hole around permeable and impermeable spur dikes. Based on the dimensional analysis, the important parameters affecting the scour hole are Froude number, permeability of the spur dike, and the ratio of flow depth to the length of the spur dike, the ratio D50 to the spur dike length and the channel width-to-length ratio. The results showed a significant reduction in the maximum permeability of scour depth compared to an impermeable spur dike, and there were also relationships for maximum scour depth.