In recent years, it has become clear that plastic pollution poses a significant threat to aquatic environments and human health. Rivers act as entry points for land-based plastic waste, while a certain fraction of entrained plastics is carried into marine environments. As such, the accurate modelling of plastic transport processes in riverine systems plays a crucial role in developing adequate remediation strategies. In this paper, we review the two main multiphase flow numerical approaches used in plastic transport modelling, comprising Lagrangian Transport Models (LTMs) and Eulerian Transport Models (ETMs). Although LTMs and ETMs can be regarded as complementary and equivalent approaches, LTMs focus on the transport trajectories of individual particles, whereas ETMs represent the behaviour of particles in terms of their mass or volume concentrations. Similar results of the two approaches are expected, while our review shows that plastic transport models are yet to be improved, specifically with respect to the formulation and implementation of boundary conditions, comprising plastic interactions with the channel bed, river bank, and the free surface, as well as interactions with biota. We anticipate that an implementation of these boundary conditions will allow better representing different plastic transport modes, including bed load, suspended load, and surface load. Finally, we provide suggestions for future research directions, including a novel threshold formulation for free surface detachment of plastics, and we hope that this review will inspire the plastic research community, thereby triggering new developments in the rapidly advancing field of numerical plastic transport modelling.

中文翻译：

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河流系统中的数值塑性输运建模：边界条件的回顾和制定


近年来，塑料污染对水生环境和人类健康构成重大威胁。河流是陆地塑料垃圾的入口点，而一部分夹带的塑料被带入海洋环境。因此，河流系统中塑料运输过程的准确建模在制定适当的修复策略方面起着至关重要的作用。在本文中，我们回顾了塑料输运建模中使用的两种主要多相流数值方法，包括拉格朗日输运模型 （LTM） 和欧拉输运模型 （ETM）。尽管 LTM 和 ETM 可以被视为互补和等效的方法，但 LTM 侧重于单个粒子的传输轨迹，而 ETM 则表示粒子的质量或体积浓度方面的行为。两种方法的结果是预期的，而我们的综述表明塑料输运模型还有待改进，特别是在边界条件的制定和实施方面，包括塑料与河床、河岸和自由表面的相互作用，以及与生物群的相互作用。我们预计，这些边界条件的实现将允许更好地表示不同的塑性传递模式，包括床载荷、悬浮载荷和表面载荷。最后，我们为未来的研究方向提供了建议，包括塑料自由表面分离的新型阈值公式，我们希望这篇综述能够激发塑料研究界的灵感，从而引发快速发展的数值塑料输运建模领域的新发展。