**5. Conclusions**

In this study the settling of mesoplastic particles of varying sizes in water was investigated. Settling times and downstream distance travelled by particles were measured experimentally. Numerical simulations were performed with three different approaches and compared to the experimental results. The computational effort was reduced by reducing the size of the domain (length of channel), and special care was taken to ensure the correct velocity profile was calculated at the position where particles were introduced into the domain, as the velocity profile of the water influences the velocity of the particles. The following conclusions can be drawn from this research:


The investigated approaches for simulation of particle settling in an open-channel flow can be used on a larger scale to predict the propagation of mesoplastics in rivers.

**Author Contributions:** Conceptualization, I.B.; methodology, E.Ž.; software, L.K.; validation, L.L. and L.K.; writing—original draft preparation, L.K.; writing—review and editing, I.B., L.L. and E.Ž.; visualization, I.B. and E.Ž.; supervision, I.B.; project administration, L.K. and L.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** The authors wish to thank the Slovenian Research Agency (ARRS) for their financial support within the framework of the Research Programme P2-0196 Research in Power, Process and Environmental Engineering. This paper is the result of a project on the Development of Research Infrastructure at the University Campus in Rijeka (RC.2.2.06-0001), cofunded by the European Regional Development Fund (ERDF) and the Ministry of Science and Education of the Republic of Croatia.

**Data Availability Statement:** All data are contained within the article.

**Acknowledgments:** The authors wish to thank Duje Kalajži´c for his help in the experiments.

**Conflicts of Interest:** The authors declare no conflict of interest.
