Groynes Placement Angle Pattern to The Depth of Erosion at the River Bend

Abstract

Abstract— This study aims to determine the pattern of cribs collapse at river bends and the effect of the slope angle of the cribs not escaping the water as a cribs collapse control as well as sediment control in channels with various bend angles. The model was made in a channel 25 × 20 cm, a river length of 600 cm. Sediment distribution from fine sand that is not homogeneous and the flow is clear (clear water). The angle and distance of the cribs installation are varied. The cribs used in this experiment were 5 cribs with a tilt angle of 30° and 60°. Each treatment was observed with parameters related to erosion and sedimentation in the river bank bends, including velocity (v), time (t), depth of erosion (de), sedimentation (ds). The dimensional analysis method is used to see the relationship between dimensionless parameters with the Langhaar method. The results showed that the maximum relative sedimentation (ds5/t)max for the crib angle of 30° occurred in the fifth crib of 0.025 at a relative speed (v/t) of  0.06. While the maximum relative erosion depth (ds3/t)max for the tilt angle of 30° crib occurs in the first grout, which is 0.012 at a relative speed (v/t) of 0.0042. At the angle of 60° cribs, there is a maximum relative erosion depth (ds3/t) of 0.082 at a relative speed (v/t) of 0.006 on the third crib. The increasing of the relative velocity (v/t) the greater the value of the relative erosion depth (ds/t).