Shields Diagram and the Incipient Motion of Microplastic Particles

This researchnewly shows that, when suitably generalized,the Shields diagram (as commonly used for sediments) can predict incipientmotion thresholds for both native sediments and foreign (microplastic)particles alike.

Incipient motion conditions for 57 regular (spheres,cylinders,disks, square plates, cubes, square prisms, rectangular prisms, tetrahedrons,and fibers) and eight irregular microplastic particle groups, havingvarious sizes and densities, are investigated in a circular flume.The present data set is combined with additional data from the literatureand systematically analyzed. A new framework is developed for predictingincipient motion conditions for foreign particles, accounting forvariations in static friction, hydraulic roughness, and hiding-exposureeffects. Via this framework, incipient motion conditions for microplasticparticles lying on a sediment bed are, for the first time, reconciledwith the classical Shields diagram.