Abstract

An experimental analysis of the dynamics of avalanches for different stages of development and turbulent flow conditions is introduced. Experiments were conducted in a laboratory flume using clear-water conditions and a video camera placed within an acrylic cylinder. The results of a proper orthogonal decomposition of the pre-processed image sequences highlighted the existence of two types of sand avalanches: Type I corresponding to a narrow and vertically long-advancing slide, and Type II characterized by an elongated and short-advancing pattern. Temporally speaking, sand avalanches were triggered aperiodically, resembling the behaviour of the horseshoe vortex system. The frequency of occurrence of avalanches decreased with time, while the estimated volume of mobilized sand increased in the same period. The sand slide magnitudes and associated inter-avalanche time were Log-Pearson 3 distributed. Sand avalanches are an important scour mechanism, which depending on the flow intensity contribute to about 40% to 60% of the scoured volume.