Experimental Study on Nearshore Transport of Buoyant Plastic Particles Under Irregular Waves

The dynamics of plastic debris in coastal areas is a complex phenomenon influenced by multiple processes, including wave breaking and coastal currents. These processes govern key outcomes such as beaching, recirculation, and along-shore or cross-shore transport of plastics. This study presents an experimental investigation of the transport velocity of macro- and mesoplastics under random wave conditions using a laboratory wave flume. Three types of plastic particles with different shapes, sizes, and densities were tested in nine hydrodynamic scenarios. The transport velocity of each sample was analysed in terms of dimensionless parameters using video analysis. Results show a strong correlation between particle buoyancy (expressed through the Dean number) and transport dynamics. The most buoyant particles show higher transport velocities up to about 9 times the wave-induced Lagrangian fluid particle velocity in deep water, while the most inertial particles show a transport velocity equal to or lower than the fluid particle velocity. These results will help improve predictive models of plastic dispersion and accumulation in coastal areas, providing useful insights for mitigation and remediation strategies.