Experimental Investigation on the Effect of Length and Angle of Groynes on Velocity and Shear Stress Distribution in a 90 Degree Bend

Groynes structures are among effective and common hydraulic structures for bank protection along bends. In the present paper, the effects of series of groynes along a 90 degree mild bend on flow characteristics such as flow and shear stresses distribution have been investigated. Tests were carried out in a bend flume having 0.7 m width, the R/B ratio for the channel bend is 4 and depth of flow for all test kept constant 0.14 m. Groynes were non-submerged and they have been used in three different lengths which are 15, 20 and 25% of channel width and three different angles including 60, 90 and 120 degrees. Also the distance between spurs was equal to 3 times of their length. The analysis of data showed that the high velocity zone moves toward center of channel and inner wall. The relative shear stresses were significantly increased by increasing the length of spure dikes and theirs elongation causes the relative shear stress multiplication up to 6 times. However, the length and angle of spurs have not had significant effect on the position of the maximum relative shear stresses along the bend. Nevertheless, the maximum relative shear stresses happened in a cross section between 70 to 80 degrees of the bend (almost end of the bend) for all experiments.