Active interactions between turbulence and bed load: Conceptual picture and experimental evidence

This paper reports results from experiments with simultaneous measurement of areal bed-load sediment concentration and water velocity (horizontal and vertical components) made at 1.5 particle diameters above the mean bed. The same spatial and temporal scales were employed to measure the kinematic properties of flowing water and sediments. The obtained data, covering a range of low sediment discharges, were analyzed in terms of bulk statistics, autocorrelation and cross-correlation functions, and quadrant decomposition of fluctuations. At the lowest transport rates, the motion of sediment particles was found to be mostly associated with sweep events. However, with increasing flow rate and bed-load discharge, the process mechanics changed, and the transport of sediments was also found to be significantly correlated with ejections. The obtained results are integrated into a conceptual picture attempting to bridge previous depictions of the bed-load transport mechanics.