ABSTRACT
The processes underlying sediment transport at grain scale are not fully understood. A method to scale down the mechanics from stream reach to bedforms and further to grains and vice versa, remains to be developed. In this study we recorded sediment transport over bedforms and initial sand waves in a laboratory study, in unsteady and non-uniform conditions. High-frequency imaging was used to obtain local measurements of the flux. Importantly, flow patterns and sediment transport were not disturbed during the measurement recordings. Particle velocities were measured using particle image velocimetry (PIV) and the volume of particles in motion is determined from a combination of image processing methods. Transport increases over the bedform. We quantify the variations over different dune shapes and sizes, and perturbations from superposed features. The observed variability in the local sediment fluxes indicate that the transport quickly responds to the unsteady and non-uniform flow over the bed.
