Experimental investigation on the effect of length, space and shape of Gabion Groynes on local scouring depth

Protecting the river bank by using groynes is very common in river engineering projects. Spur dikes makes flow path to be modified. Because of the concentration of flow in middle part of the river side is washed out. Settling spur dikes in the flowʼs direction lead to a local scour in the spur dike side and the change in the bed topography. In this investigation a laboratory movable bed flume with 18 m length, 1.5 m width and 0.8 m depth was used. To study local scour near the head of unsubmerged gabion groynes, the groynes were constructed perpendicular to the flumeʼs wall. Two shapes of groynes (L shape and T shape), two constriction ratios(20% and 30%) and four ratios of space to length (S/L), were used with one constant bed material and one constant bed slope with three different discharges. Since the reduction of flow velocity between two consequent groynes, causes sedimentation and bank protection, all of the experiment were repeated withconstant bed. In this experiment the flow velocity and the pattern of streamlines between consequent groynes were investigated with more details. Based on the experiments result for L shape groyne S/L=3 and for T shape groyne S/L=4 is recommended as the most suitable S/L ratios. Regarding the type and shape of groyne, T shape groyne indicated the least scouring depth.