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Discussion papers
https://doi.org/10.5194/esurf-2019-8
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/esurf-2019-8
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 27 Feb 2019

Research article | 27 Feb 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Earth Surface Dynamics (ESurf).

Experiments on patterns of alluvial cover and bedrock erosion in a meandering channel

Roberto Fernández1, Gary Parker1,2, and Colin P. Stark3 Roberto Fernández et al.
  • 1Ven Te Chow Hydrosystems Laboratory, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
  • 2Department of Geology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
  • 3Lamont Doherty Earth Observatory, Columbia University, Palisades, NY 10964, USA

Abstract. In bedrock rivers, erosion by abrasion is driven by sediment particles that strike bare bedrock while traveling downstream with the flow. If the sediment particles settle and form an alluvial cover, this mode of erosion is impeded by the protection offered by the grains themselves. Channel erosion by abrasion is therefore related to the amount and pattern of alluvial cover, which are functions of sediment load and hydraulic conditions, and which in turn are functions of channel geometry, slope and sinuosity. This study presents the results of alluvial cover experiments conducted in a meandering channel flume of high fixed sinuosity. Maps of quasi-instantaneous alluvial cover were generated from time-lapse imaging of flows under a range of below-capacity bedload conditions. These maps were used to infer patterns of particle impact frequency and likely abrasion rates. Results from eight such experiments suggest that: (i) abrasion through sediment particle impacts is driven by fluctuations in alluvial cover due to the movement of freely-migrating bars, (ii) patterns of potential erosion are functions of sediment load and local curvature, (iii) low sediment supply ratios are associated with regions of potential erosion located closer to the inner bank but this region moves toward the outer bank as sediment supply increases, and (iv) the threads of high erosion rates are located at the tow of the alluvial bars, just where the alluvial cover reaches an optimum for abrasion rate.

Roberto Fernández et al.
Interactive discussion
Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Roberto Fernández et al.
Data sets

Experiments on patterns of alluvial cover and bedrock erosion in a meandering channel. R. Fernández, G. Parker, and C. P. Stark https://doi.org/10.13012/B2-3044828_V1

Model code and software

Experiments on patterns of alluvial cover and bedrock erosion in a meandering channel. R. Fernández, G. Parker, and C. P. Stark https://doi.org/10.13012/B2-3044828_V1

Video supplement

Evolution of alluvial cover (19% mean cover) R. Fernández https://doi.org/10.5446/40247

Evolution of alluvial cover (27% mean cover) R. Fernández https://doi.org/10.5446/40246

Evolution of alluvial cover (38% mean cover) R. Fernández https://doi.org/10.5446/40245

Evolution of alluvial cover (46% mean cover) R. Fernández https://doi.org/10.5446/40244

Evolution of alluvial cover (54% mean cover) R. Fernández https://doi.org/10.5446/40243

Evolution of alluvial cover (72% mean cover) R. Fernández https://doi.org/10.5446/40242

Evolution of alluvial cover (79% mean cover) R. Fernández https://doi.org/10.5446/40241

Erosion front (19% mean cover) R. Fernández https://doi.org/10.5446/40240

Erosion front (27% mean cover) R. Fernández https://doi.org/10.5446/40239

Erosion front (38% mean cover) R. Fernández https://doi.org/10.5446/40238

Erosion front (46% mean cover) R. Fernández https://doi.org/10.5446/40237

Erosion front (54% mean cover) R. Fernández https://doi.org/10.5446/40236

Erosion front (72% mean cover) R. Fernández https://doi.org/10.5446/40233

Erosion front (79% mean cover) R. Fernández https://doi.org/10.5446/40232

Roberto Fernández et al.
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Short summary
Rivers with different patterns flow over different materials. We describe the case of a meandering bedrock river with loose sediment (sand or gravel) on the bed. In such rivers, the sediment hits and erodes the bed as it moves with the flow. We did experiments in a laboratory flume to identify the areas where the sediment moves and those where it deposits. We discovered that those areas change with the amount of sediment in the channel and its curvature. The rate of change is very important.
Rivers with different patterns flow over different materials. We describe the case of a...
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