Laboratory Investigation on the Effect of Spur Dike Permeability on the Scour Hole Dimensions

Spur dike use is one of the most common structural methods for improvement and bank protection in river engineering. This structure is generally built across the river from the bank towards centerline in order to protect the banks from erosion and to increase sedimentation along the protected banks. However، the scour hole around the nose of the structure is formed due to reducing flow width and increasing velocity and shear stress. In order to investigate the effect of permeability of spur dikes on scour hole dimensions، experiments were carried out in a laboratory flume with 7. 3m length، 0. 56m width and 0. 6m depth. Four quantities of permeability including 0% (impermeable)، 30%، 40% and 50% with four Froude numbers at constant flow depth (0. 15m) were conducted and all experiments were carried out with clear water. of the bed sediments was equal to 0. 7mm. Dimensional analysis was applied to produce the related non-dimensional parameters and by using the measured data and regression analysis a few equations for estimating scour hole dimensions were developed. The results showed that with increasing Froude number the scour hole dimensions increased up to 1. 5 times (in non permeable condition). The maximum scour hole depth increased up to 4 times، whereas the spur dike permeability decreased from 50% to 0%. The scour hole dimensions for the first and second spur dikes were also decreased by increasing the spur dike permeability.