Application of GRA Method in Optimization of Length and Location of Spur Dike in 90 Degree Bend

Spur dikes، as hydraulic structures، are used to protect river banks against scouring. Spur dike in river bends، where secondary flow causes more erosion around outer bank، can be used as a protection mean. When spur dikes are installed in a bend، a complicated flow pattern is formed، especially around the spur dike. Geometrical parameters of spur dike and bend plus hydraulic parameters of flow، affect flow pattern resulting from interaction of spur dike and bend. Understanding the effects of different parameters on spur dike operation and flow pattern will help the effectiveness of the spur dikes. In this paper، flow pattern around spur dike in a bend was simulated numerically by variation of length and location of spur dike at different hydraulic conditions. Then، considering hydraulic operation and structural stability of spur dike، GRA method was used for optimizing composition of length and location of spur dike at different Froude numbers. The results show that the length of spur dike is more effective than its location on spur dike operation. If stability of spur dike is taken into consideration، spur dike will have better operation when it is installed at any location with length of 25% of the channel width.