minerals Article Infiltration Depth of Mineral Particles in Gravel-Bed Rivers Natalia Bustamante-Penagos 1, * and Yarko Niño 1,2,3, *   Citation: Bustamante-Penagos, N.; Niño, Y. Infiltration Depth of Mineral Particles in Gravel-Bed Rivers. Minerals 2021, 11, 1285. https:// doi.org/10.3390/min11111285 Academic Editor: Mark I. Pownceby Received: 11 October 2021 Accepted: 10 November 2021 Published: 19 November 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Civil Engineering, Faculty of Physical and Mathematical Sciences, Universidad de Chile, Santiago 8370449, Chile 2 Advanced Center for Water Technologies, Santiago 8370448, Chile 3 Advanced Mining Technology Center, Faculty of Physical and Mathematical Sciences, Universidad de Chile, Santiago 8370449, Chile * Correspondence: nataliabustamante@ug.uchile.cl (N.B.-P.); ynino@ing.uchile.cl (Y.N.) Abstract: This article discusses the results of an experimental study of a spill of mineral particles in gravel-bed rivers due to mining accidents. The purpose of this research is to characterize the dynamics of the fine mining particles spilled on a bed of immobilized gravel as a hyper-concentrated mixture and to experimentally characterize the infiltration phenomenon. We analyzed the type of infiltration considering the dimensionless coarse to fine particle size relationship, the dimensionless weight of the fine particles, the relative density of the particles, and the relationship between the subsurface and surface velocities, in addition to the densimetric Froude and Reynolds numbers of the fine particles. We found that the dimensionless infiltration depth is not associated with hydraulic parameters or the weight of the fine sediment spilled; however, fine sediment deposition decreases with depth, and infiltration depth may increase if subsurface flow decreases over time. Finally, a relationship of the dimensionless maximum infiltration depth with the relative density of the mining particles, the ratio of the bed sediment and the mining particles sizes, and the ratio between the subsurface and surface velocities is established. Keywords: infiltration of fine materials; pollution by mining materials; unimpeded static percolation; bridging; clogging 1. Introduction Heavy metals in riverbeds can come from acid rock drainage formation, mining, industry, or mining accidents. As a result of current and historical metal mining, rivers and floodplains in many parts of the world have become contaminated by the metal-rich waste in concentrations that may pose a hazard to human and animal livelihoods [1–3]. Human health and environmental impacts commonly arise due to the long residence time of heavy metals in river sediments and alluvial soils and their bioaccumulatory nature in plants and animals [2]. Coulthard et al. [1] modeled heavy metal contamination in river systems in the United Kingdom. Simulations considered sediment transport dynamics to analyze contaminant transport due to sediment movement. An increase in flow rate may reduce contamination because it could generate bedload transport, and further dilution may occur. Jaskula et al. [4] analyzed the spatial variability of riverbed pollution by heavy metals, such as Cr, Ni, Cu, Zn, Cd, and Pb, in sediments of the Warta riverbed in Poland. They found that the highest contributors to pollution were urbanized areas and industrial activities. They also reported the temporal variability of heavy metals and that the ecological risk is proportional to the presence of heavy metals in the riverbed. Several mining accidents have occurred worldwide. Benito et al. [5] studied the Aznalcollar mine spill in 1998. The accident caused the spilling of some 4.5 × 10 3 Mm 3 of acid water and pyrite ore, generating a waste sludge with a high concentration of heavy metals in the floodplains of the Agrio and Guadiamar rivers, Spain, affecting the Minerals 2021, 11, 1285. https://doi.org/10.3390/min11111285 https://www.mdpi.com/journal/minerals