Accurately modeling microplastic (MP) transport in rivers requires a deep understanding of their transport mechanisms. However, the transport behavior of microplastics (MPs) under moderate flow conditions, where their near-bed movement is intermittent, remains poorly understood. This study addresses this gap by conducting particle tracking experiments under flow conditions near the threshold of MP mobilization in open channel flows. The analysis focuses on the stochastic nature of MP streamwise movements. A statistical description for the key kinematic variables was developed, including MP streamwise velocity (vx), hop length (Lx), and hop duration (Ttr). The results showed that both Lx and Ttr followed exponential distributions and that a truncated Gaussian distribution provided the best fit for vx. Analysis of the relationship between Lx and Ttr revealed that, on average, approximately 60% of MP hops across all experimental cases corresponded to "long hops", which are characterized by Lx ∝ Ttr. Relative to pristine MPs, aged MPs had approximately 30% lower surface roughness, with negligible differences in the kinematic variables. In addition, the vx correlation time scales were comparable to the particle response times, showing that particle inertia contributes to the temporal persistence of vx variations and to the lagged adjustment of vx to fluid drag.
Yu et al. (Wed,) studied this question.