The spatiotemporal evolution of fine tailings in sand-bed rivers

Rojas Aguirre, Andres Felipe

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https://hdl.handle.net/2142/122202 Copy

Description

Title

The spatiotemporal evolution of fine tailings in sand-bed rivers

Author(s)

Rojas Aguirre, Andres Felipe

Issue Date

2023-09-28

Director of Research (if dissertation) or Advisor (if thesis)

Garcia, Marcelo H

Doctoral Committee Chair(s)

Garcia, Marcelo H

Committee Member(s)

• Parker, Gary
• Best, James L
• Tinoco Lopez, Rafael O
• Viparelli, Enrica

Department of Study

Civil & Environmental Eng

Discipline

Civil Engineering

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Iron tailings
• Exner equation
• sediment density
• Engelund-Hansen equation
• Entrainment
• Annular Flume
• Settling column
• Tailings pulse
• Downstream lightening
• Upward heavying
• Bedforms

Abstract

The spreading of mine tailings in riverine systems has been studied through classical morphodynamics evolution analysis limited to natural sediment conditions. However, the density of tailings can differ substantially from the density of natural sediment in rivers due to the tailing's mineralogical composition. To overcome the density difference between materials, a 1D mathematical formulation based on the active layer concept is developed to predict the spatiotemporal evolution of a mixture of two materials with different densities interacting in a watercourse within the active layer and in the substrate. This formulation is based on the assumption of a strong correlation between the density of the tailings and mineral content (or metals). Herein, this formulation estimates the spatiotemporal evolution of the spreading of a single iron tailings pulse deposited in the Paraopeba River (Brazil) on January 25, 2019. Since the sediment density and content of iron tailings have a strong correlation, the sediment density is used as a surrogate to track the temporal distribution of the iron tailings along the river. The model formulation aims to determine the sediment density evolution for different fractions within the active layer and in the substrate. The analysis also includes a re-calibration for the Sorting Engelund-Hansen Equation, SEH (An et al.,2020), as the original parameters were determined based on experiments in large flumes that are of limited application in sand-bed rivers. The SEH equation is selected due to the lack of bed and suspended load formulations developed for rivers with substantial amounts of iron tailings in a riverbed. The field measurement campaigns conducted along rivers affected by iron tailings deposition (i.e., Doce River and Paraopeba River) demonstrate the predominance of sand-tailings mixtures to move in suspension. Hence, such suspension component can be determined by using the vertical velocity profile and the suspended sediment distribution for equilibrium conditions. This approach requires the determination of the near-bed concentrations that are usually estimated via sand-based formulations. As the presence of iron tailings is not typically found in riverbeds, this research aims to determine whether sand-based formulations reasonably predict near-bed concentrations of two poorly-sorted iron tailings samples subjected to bed shear stress in an annular flume. One of the main findings of this research is that the near-bed concentrations can be predicted by adding two dimensionless parameters to the sand-based entrainment formulations: the relative roughness (H/D) of the sample and the particle Reynolds number (Repi) for fractions smaller than the thickness of the viscous sublayer (δv). Finally, this thesis explores the mechanisms that govern the spreading of a single pulse of heavy and fine iron tailings moving along a sand-bed river and the impact the downstream aggradation has on water stages. To reach these objectives, this dissertation uses the field measurements database from the Paraopeba River, as this watercourse has been continuously monitored after the tailing dam breach that led to an uncontrolled deposition of iron tailings into the river. The analysis demonstrates that a combination of translation and dispersion are the mechanisms that govern the spreading of this single pulse. The translation component is explained by the fact that these tailings are dynamically more movable than the ambient sand, even though they are heavier than the ambient sand of the river. On the other hand, the dominance of dispersion is explained mainly by the morphology of the river, the low-velocity zones, the mixing of the tailings with the ambient material, and tailings burial in the river substrate. This study also shows that the river's water surface elevations (WSE) are not sensitive to the aggradation nor the smoothing of the riverbed generated by the spreading of the iron tailings, as bedrock outcrops and pool-riffle sequences highly control the river hydrodynamics.

Graduation Semester

2023-12

Type of Resource

Thesis

Copyright and License Information

Copyright 2023 Andrés Felipe Rojas Aguirre

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