Bank protection at the outer side of curved channels by an undulated macrorough concrete wall

Systematic hydraulic model tests were performed in a 90° curved channel with an undulated wall at the outer bank. The outer wall consisted of trapezoidal elements of 0.1 m depth and 0.33 m length. Three discharges (150, 180 and 210 l/s) and three bed slopes (0.35, 0.5 and 0.7%) with a wide grain size distribution of the bed sediments (dm = 8.7mm) were tested. The following parameters for subcritical flow conditions were studied: bed morphology, water level, sediment transport, longitudinal water velocities and grain sorting across the bend. Based on the experiments, two principal scour holes could be identified. Compared to the case of a smooth wall (without undulations) the depth of the two scour holes was significantly reduced. The reduction was about 20% at the first hole and 40% at the second one. The scour location was also influenced by the undulations. Compared to the smooth wall the two scour holes were shifted by 10° in downstream direction.