A transport and accumulation model for macroplastics in rivers

ABSTRACT: We present a novel model that simulates macroplastic transport and retention in rivers, and which explicitly considers plastic accumulation in floodplains. The modelling ap-proach is based on a simplified representation of flow distributions between river channel and floodplains in non-uniform compound channels. In the model, transported and deposited macro-plastics en route to the sea are linked to flow exchanges between the river’s main channel and its floodplains. A key assumption in the model is that the macroplastic retention rate for transported macroplastics is much higher in the floodplain than in the main channel. We apply the model to the Dutch river Meuse and show that predicted macroplastic accumulation sites on the floodplains are in good agreement with observations of accumulation zones following a recent flood event. This shows that the model captures the dominant transport processes of macroplastics in rivers and thus offers insight into the occurrence of macroplastic accumulation sites in rivers. Next, we show how the model can be used to estimate the yearly budgets between retained and transported macroplastics. Finally, we argue that the model can be used to improve monitoring schemes and for the design of effective clean-up strategies.