Plastic debris in waves: an experimental study

Plastic waste in the ocean is one of the most consequential issues of humankind. Statistics show that approximately 12 million tons of plastic are dumped into the ocean and a total of 268,940 tons of plastic consisting of 5.25 trillion particles are distributed over the surface every single year (Jambeck, 2015). However, little knowledge has been acquired about the effect of local wave on plastic particle movement. In this study, the issue of local wave effect has been studied to investigate the trajectories and distribution of the plastic particles on the free water surface. A series of model tests have been performed. For regular wave tests, factors including a single and a flock plastic, different frequencies are considered, and for irregular wave tests, five different sea states are taken into consideration. The experimental results showed a correlation between the wave frequency and the final position of the plastic particles. Specifically speaking, under the circumstance of fixed altitude, when the frequency is higher than 1.2Hz, the majority of the particles will end up on shore, and a higher frequency will lead to a faster landing. Similar phenomenon was observed in the irregular wave test, where the possibility of landing at lower sea states are higher than that at higher sea states. Results and observations gained from this research can contribute to our understanding of the marine pollution issue and help predicting the landing time of waste in coastal area as well as creating a more accurate estimation of the distribution of ocean plastic in seabed.