The Impact of Intermittency on Bed Load Sediment Transport

Abstract

Sediment transport by wind and water shapes many of Earth's landscapes. Models that predict how rapidly a flow can move sediments are essential for understanding the evolution of Earth's surface (Anderson & Anderson, 2010; Bridge & Demicco, 2008), mitigating risks posed by natural hazards, designing engineering structures that will interact with moving sediment (

Fluid‐Driven Transport of Round Sediment Particles: From Discrete Simulations to Continuum Modeling

“…Overall, in terms of the q* versus τ* transport relation, the DEM-LBM simulations are consistent with the experiments. At the lowest Shields number simulated, τ* = 0.023 ( 𝐴𝐴 𝐴𝐴 * 𝑐𝑐 found to be 0.026 ± 0.002 (Benavides et al, 2021)), we observe strong intermittency (see Movie S1). With the standard initialization, the transport of particles eventually ceases, giving q* = 0 (marked as 0.002 in Figure 3a due to semi-log).…”

“…See Appendix B for more details. Deal et al (2021) and Benavides et al (2021) conducted bedload sediment transport experiments with glass spheres in a narrow flume, and recorded high-speed videos of the grains, allowing for precise tracking. This provides abundant details of the particle motion.…”

“…To ensure the fluid velocity in the Discrete Element Method-Lattice Boltzmann Method (DEM-LBM) simulations, it is correct is crucial to recover the transport relation of the sediment particles. In the flume experiments (Benavides et al, 2021;Deal et al, 2021), the flumes are narrow and tall so that the cross-sectional fluid streamwise velocity far from the granular bed can be approximated by the law of the wall when fully developed. According to the law of the wall, the velocity near the wall (viscous sublayer, y + < 10.8) is linear to the wall distance u + = y + with y + = y w u τ /ν f , 𝐴𝐴 𝐴𝐴𝜏𝜏 = √ 𝜏𝜏𝑤𝑤∕𝜌𝜌𝑓𝑓 and u + = u/u τ , where y w is the distance to the closest wall of the channel and τ w is the wall shear stress.…”

“…In the following discussion of the particle-scale simulations, we first introduce the DEM-LBM numerical method. Second, we present simulations matching the conditions of flume experiments (Benavides et al, 2021;Deal et al, 2021) to provide a relevant many-particle test of the methodology. Third, we present wide wall-free (WWF) simulations in order to study the factors that can potentially cause the variability seen in experimental transport data on gentle slopes.…”

“…Then it is quantified as a "rotation stress" whose profile is examined in different transport stages and further correlated to the transport relation. Our work here is benchmarked by flume experiments (Benavides et al, 2021;Deal et al, 2021) in which grain-scale motions were tracked. (b) What is (not) responsible for the variability in the observed sediment transport relation?…”