Author(s): T. Ganz; F. Schoberl
Linked Author(s): Friedrich Schöberl
Keywords: Flow instabilities; Steep rivers; Stepped rivers; Mudflow
Abstract: Steps or cascade-drops are common measures for reducing flow energy and preventing bed erosion in torrents. In such a stepped reach of a steeper alpine river in Austria flow instabilities occurred during a flood. This study aims at analysing the boundary conditions responsible for the observed wave trains, which developed spontaneously from stable flow, in a scale model 1:40. The experimental device consists of a straight, trapezoidal channel furnished with cascadedrops of constant step geometry. The slope of the flume is adjustable up to 10% inclination and the maximum discharge amounts to 70 l/s. Significant parameters influencing the emergence of flow instabilities are the flow discharge, slope and geometry of the cascades. The main characteristics of the self-generated wave trains are the increase of wave amplitude along the flume and the appearance of flow instabilities between a lower and an upper limit of flow discharge. With decreasing slope these limits coincide. Moreover, the investigations reveal the evolution of the maximum wave height depending on the available development length and the influence of the bed geometry on the wave formation.
Year: 2003