At the Water Resources Institute of the University of Innsbruck experiments have been performed in an S-shaped trapezoidal channel with two bends and a slope of S = 0,01 ― with both fixed and erodible beds. Gravel with a mean diameter between 4,2 mm and 6,4 mm was used as bed material and for sediment feeding. Velocities were measured by means of a two-dimensional electromagnetic current meter. The analysis of the sxpriments yields a new function for the radial distribution of the depth-averaged longitudinal velocities that differs from the forced vortex approach. It is also shown that in the case of an erodible bed the redistribution of flow ― as a consequence of the evolution of scour on the outer and deposition on the inner bank ― leads to completely different radial velocity distributions compared with the initial bed.
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