Author(s): Alexandre Duarte; Koen Blanckaert; Anton J. Schleiss
Keywords: Open-channel bends; Secondary circulation; Bank roughness
Abstract: In foregoing experiments on flow in open-channel bends, a complex flow pattern was observed near the outer bank, which is relevant for the design of bank protection schemes in river restoration projects. This paper investigates the influence of outer bank roughness on the flow pattern in a sharp laboratory open-channel bend with rectangular cross-section by means of high-resolution three-dimensional velocity measurements with an Acoustic Doppler Velocity Profiler. In all experiments, the pattern of cross-stream circulation is characterized by the existence of center-region cell and a counter rotating outer bank cell that strongly determine the downstream velocity pattern. With increasing outer bank roughness, the outer bank cell amplifies and widens considerably. It exerts a protective effect on the outer bank. The widening of the outer bank cell with increasing roughness of the outer bank crushes the center region cell in towards the inner bank, but does not significantly modify the evolution of its strength around the bend. Research is currently extended by investigating the effects of different inclinations of the outer bank.