Two-dimensional simulation of plastic bottles transport in a urban reach of the Arno River

Abstract

Within the MINOSSE project (ManagINg plastic transpOrt in riverS and coaStal arEas), the 2D hydrodynamic numerical model ORSA2D_WT has been adapted to simulate the transport of plastic bottles, the most common macroplastic item transported in water bodies. Unlike smaller plastics, such as fragments or films, the shape and size of plastic bottles can significantly influence their inertia and fate. They may not follow flow velocity lines, so they must be modelled as discrete items, driven by the flow field and capable of interacting with surrounding elements (riverbed, riverbanks, bridge piers, vegetation, other debris of plastic or different nature). Thanks to the proposed 2D numerical approach, they are modelled as individual items floating on the water surface or being conveyed in the water column. The ORSA2D_WT model has been appled to simullate plastic bottles trajectories in a 7.6 km urban reach of the Arno River, during a winter event. Two different releases points were considered, the Affrco conflunece on the side of the river and a central point of the river close to the upstream section. The results of the model from the release points show a different behaviuor in the trajectories and in the stranding points. These first results qualitatively match the in situ observations, and show that the numerical model can help in identifying hot spots for plastic accumulation.