Validating a universal model of particle transport lengths with laboratory measurements of suspended grain motions

Abstract

AbstractThe mechanics of sediment transport are of fundamental importance for fluvio‐deltaic morphodynamics. The present study focuses on quantifying particle motions and trajectories across a wide range of flow conditions. In particular, a continuous model is presented that predicts particle travel distances for saltation and suspension based on Rouse number and relative grain roughness. By utilizing a series of eight video cameras in a plexiglass flume direct measurements of the distributions of particle travel distances (excursion lengths) were obtained. To this end, experiments were carried out in dark under black lights with fluorescent painted plastic and quartz sand particles. For relatively high Rouse numbers indicating bed load dominant transport regime ( ), particle motion is governed by the effect of gravitational forces (settling velocities) and measured excursion lengths closely follow a Gaussian distribution. For , particle motion is equally subjected to both gravitational and turbulent forces. Consequently, measured excursion lengths exhibit a bimodal distribution with two distinct peaks. As turbulent fluctuations increase and dominate particle motion over gravity ( ), distributions of excursion lengths become unimodal and negative‐skewed with mean values deviating from the modes. The predicted trend of linearly increasing excursion lengths with decreasing Rouse numbers is consistent with measured excursion lengths across a wide range of Rouse numbers ). Furthermore, measured excursion lengths are observed to fit within the predicted range of excursion lengths with no significant difference between measured excursion lengths of plastic and quartz sand particles.