2025 CSDMS meeting-100
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Flow-driven bedload: A numerical study of monodisperse and bidisperse grain kinematics
Anshul Yadav,
(He/Him),University of Rochester Rochester New York, United States. ayadav3@ur.rochester.edu
Rachel Glade, University of Rochester Rochester New York, United States. rglade@ur.rochester.edu
The kinematics of sediment grains on a riverbed govern bedload transport, influencing water quality, aquatic ecosystems, river morphology, and landscape evolution. Previous studies suggest that hop distance distributions exhibit Gaussian-like behavior for large hops and exponential-like behavior for a mixture of short and long hops. Assuming flow hydraulics as the primary driver of these variations in hops, we numerically investigate the effects of flow conditions on the ensemble distributions of hop distances, particle velocities, travel times, and resting durations. This was done through high-fidelity simulations using coupled fluid dynamics/discrete element method (CFDEM), which integrates LIGGGHTS with OpenFOAM. For monodisperse grains (0.5 mm), hop distances follow a Weibull distribution, while velocity distributions are exponential, with scale factors increasing with flow strength. The relationship between streamwise hop distances and travel times follows Lx ∼ Tpα, with α ranging from 1.50 to 1.76. Travel times exhibit an exponential distribution, whereas resting times follow a Weibull distribution, both with scale factors increasing under higher flow conditions. For bidisperse grains (0.5 mm and 1 mm), the velocity distributions of each grain size independently follow an exponential distribution, while the combined velocity distribution conforms to a hypoexponential distribution - a weighted sum of exponential distribution of both sizes. This result suggests that, despite mechanical interactions between grains, the velocity distributions of each grain size remain statistically independent. These findings provide insight into the probabilistic nature of bedload transport and the role of flow dynamics in shaping sediment motion.
Keywords: Velocity distribution, hop distance, travel time, resting time
