Database for the setting and rising dynamics of river litter

Resolving the vertical velocities and three-dimensional dynamics of macroplastics and other anthropogenic litter is critical for developing comprehensive hydrodynamic models of litter transport in rivers – both vertically in the water column and horizontally across the channel. Employing large settling tanks, with a synchronous multi-camera system and an automated plastic detection algorithm, we reconstruct in three-dimensions the settling and rising trajectories more than 1,000 litter items. This enables characterisation of a litter item’s vertical and horizontal velocities, as well as their drifting gradient, oscillatory motions and settling patterns. Settling and rising velocity distributions are presented for 24 River-OSPAR categories, which represent approximately 80% of the most persistent litter categories found in rivers and on riverbanks, and include items such as plastic bags, food wrappers, and cigarette filters. The velocity distributions for each River-OSPAR category support realistic inputs for hydrological models of litter transport. Individual trajectories are then classified into four regimes – linear, linear drifting, nonlinear and nonlinear drifting – based on lateral displacement and zero-crossing analysis. This classification allows construction of a regime map of settling and rising dynamics as a function of a litter’s geometry and density, delineating regions in which different River-OSPAR categories exhibit distinct settling behaviours. The resulting regime map and velocity statistics provide physically based inputs for hydrodynamic models aimed at predicting the mobilisation, transport, and fate of litter in riverine environments.