THE ORIGIN OF SAND BARS AND THEIR DEVELOPMENT PROCESS IN FLUME EXPERIMENTS

Abstract

 Although many studies have been conducted on sand bars, the origin of sand bars and the mechanism of their development are still unknown. In this study, we measured the formation process of sandbars with the crossing patterns that occur from flat beds in the very early stage with high spatial resolution and high frequency. We quantified the migrating speed of the sand waves during this process based on the measurement. The results show that the migrating speed of the sand waves at the initial stage have a spatial distribution and that their transverse component is non-negligible in relation to the deformation of the sand waves. It was found that with changes in migrating speed, the high wavenumber sand waves gradually merged into the low wavenumber sand waves that are generally recognized as sandbars. These results suggest that, in the experimental cases conducted in this study, oblique crossing pattern is the origin of the sand bars.