4 th IAHR International Symposium on Hydraulic Structures, 9-11 February 2012, Porto, Portugal, ISBN: 978-989-8509-01-7 1 BANK PROTECTION AT THE OUTER SIDE OF CURVED CHANNELS BY AN UNDULATED MACROROUGH CONCRETE WALL A. Vela Giró 1 and A.J. Schleiss 2 1 INGENI SA, Lausanne, Switzerland, alexandre.velagiro@ingeni.ch 2 Laboratoire de Constructions Hydrauliques (LCH), EPFL, Lausanne, Switzerland anton.schleiss@epfl.ch Abstract: 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 (d m = 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. Keywords: channel bend, outer bank scour, bank protection, bed morphology. INTRODUCTION In valleys of the Alps and Pyrenees, rivers often pass through villages and cities. The lack of space between the river and the infrastructures requires protection by walls against floods and bank erosion. Due to bend effects, bend scour occurs near the outer bank. An extreme flood can erode the bank foundations and results in wall failure. Subsequently, uncontrolled erosion can propagate behind the failed wall and cause serious damages at buildings and infrastructures. The construction of an undulated concrete wall (Fig. 1) along the outer bank of a bend has the following advantages: 1. The undulations can reduce considerably the scour depth along the wall toe. 2. The undulations increase the constructional rigidity and stability of the wall. Even if there is scouring along the foundation, the wall undulations increase resistance against overturning by earth and water pressure behind the wall. 3. Without reducing the width of the river, the undulated wall can increase space for public use and favor architectural integration. Scour in bends has been investigated since a long time. Fargue, as one of the first researchers