Author(s): Christine Sindelar; Petr Lichtneger; Helmut Habersack
Keywords: Submerged groynes; Secondary currents; ADCP; Navigation
Abstract: In this paper the effect of repelling groynes on hydrodynamics and morphodynamcis was investigated for three different submergence levels und controlled near-natural conditions. If forms part of a larger study in which attracting groynes and scaling effects are additionally studied. The experiments were carried out in the BOKU research channel in Vienna which is run with Danube water. The flow rate was Q = 5.2 m³/s, the Froude number was 0.29 and the Reynolds number was 10⁶. The bed material was composed of gravel with a mean diameter of dm = 47 mm. It mimics the coarser fractions of the Danube bed material near Vienna. The ratio water depth to groyne height H/h ranged from 1.47 (low) to 4.4 (high). Mean velocities and strength of the secondary currents were measured and analyzed. All groyne designs redirect high streamwise velocities away from the bank. This effect increases with decreasing submergence. All groyne designs induce a clockwise-rotating motion in the groyne field which is strongest for H/h = 1.47. In contrast, the risk of scouring near the groyne tip is minimal for H/h = 4.4. While repelling groynes are mainly used to support bank stabilization, attracting groynes may serve the opposite purpose: to enhance bank erosion thus reducing the effects of river bed degradation and allowing morphodynamic processes. The research work continues to test attracting groynes at different relative submergence.