Flow separation—a physical process for the concentration of heavy minerals within alluvial channels

Best, James L.; Brayshaw, Andrew C.

doi:10.1144/gsjgs.142.5.0747

Cited by 40 publications

(15 citation statements)

References 22 publications

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“…Additionally, the process of selective grain entrainment could be reproduced by the numerical simulations, which further helps to answer the second research question. At the beginning of the simulations, with well‐mixed beds, the light particles were more frequently entrained than heavy particles, consistent with the experimental findings reported by Komar () and Best & Brayshaw (). Consequently, the light particles were subsequently separated from the heavy particles.…”

Section: Discussionsupporting

confidence: 92%

Understanding heavy mineral enrichment using a three‐dimensional numerical model

2017

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Layered deposits of relatively light and heavy minerals can be found in many aquatic environments. Quantification of the physical processes which lead to the fine‐scale layering of these deposits is often limited with flumes or in situ field experiments. Therefore, the following research questions were addressed: (i) how can selective grain entrainment be numerically simulated and quantified; (ii) how does a mixed bed turn into a fully layered bed; and (iii) is there any relation between heavy mineral content and bed stability? Herein, a three‐dimensional numerical model was used as an alternative measure to study the fine‐scale process of density segregation during transport. The three‐dimensional model simulates particle transport in water by combining a turbulence‐resolving large eddy simulation with a discrete element model prescribing the motion of individual grains. The granular bed of 0·004 m in height consisted of 200 000 spherical particles (D50 = 500 μm). Five suites of experiments were designed in which the concentration ratio of heavy (5000 kg m−3) to light particles (i.e. 2560 kg m−3) was increased from 6%, 15%, 35%, 60% to 80%. All beds were tested for 10 sec at a predefined flow speed of 0·3 m sec−1. Analysis of the particle behaviour in the interior of the beds showed that the lighter particles segregated from the heavy particles with increasing time. The latter accumulated at the bottom of the domain, forming a layer, whereas the lighter particles were transported over the layer forming sweeps. Particles below the heavy particle layer indicated that the layer was able to armour the particles below. Consequentially, enrichment of heavy minerals in a layer is controlled by the segregation of a heavy mineral fraction from the light counterpart, which enhances current understanding of heavy mineral placer formation.

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Section: Discussionsupporting

confidence: 92%

Understanding heavy mineral enrichment using a three‐dimensional numerical model

2017

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“…Best (1987) showed that avalanche faces can develop on the upstream end of these scours (Fig. Best and Brayshaw 1985), with the emergent bar acting as an obstacle within the channel. This allows the scours to be filled laterally, 167 obliquely, or vertically by an avalanche deposit in a short period of time during channel switching or a flood event.…”

Section: Hollows (Element Ho)mentioning

confidence: 99%

The Geology of Fluvial Deposits

Miall¹

2006

773

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“…They reason that this phenomenon is due to the main channel capturing more and more tributary inputs in a downstream direction, with the asynchronous timing of water and sediment contributions from upstream ephemeral tributaries producing distinct laminae at each successive confluence. Heavy minerals may also concentrate along scour surfaces and within the sediments of channel junctions, and these sites can be areas of significant heavy-mineral accumulations (Mosley and Schumm, 1977;Best and Brayshaw, 1985;Carling and Breakspear, 2006).…”

Section: Sedimentologymentioning

confidence: 99%

Sediment Transport, Bed Morphology and the Sedimentology of River Channel Confluences

Best

Rhoads

2008

River Confluences, Tributaries and the Fluvial Network

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111

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ContextRiver channel confluences are sites of significant hydraulic and morphological change within fluvial networks (Richards, 1980;Rhoads, 1987;Ferguson et al., 2006; Lane, this volume, Chapter 3) and also occur within river channels where islands or bars are present. The local and downstream effects of confluences can have a profound influence on the geomorphology and ecology of river channels -see, for example, Rice et al.-as well as on strategies for effective channel management (Pinter et al., 2004). For these reasons, the morphology of river channel confluences is of major importance within a range of considerations and disciplines. For example, scour-depth predictions at channel junctions are clearly needed in the design of engineering structures, whilst the recognition of confluence scour is important in reconstructions of ancient sedimentary environments (Bristow et al.

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Flow separation—a physical process for the concentration of heavy minerals within alluvial channels

Cited by 40 publications

References 22 publications

Understanding heavy mineral enrichment using a three‐dimensional numerical model

Understanding heavy mineral enrichment using a three‐dimensional numerical model

The Geology of Fluvial Deposits

Sediment Transport, Bed Morphology and the Sedimentology of River Channel Confluences

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