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Sediment flux driven channel geometry adjustment of bedrock and mixed gravel‐bedrock rivers

journal contribution
posted on 08.09.2020 by Edwin Baynes, Dimitri Lague, Philippe Steer, Stéphane Bonnet, Luc Illien
Sediment supply (Qs) is often overlooked in modelling studies of landscape evolution, despite sediment playing a key role in the physical processes that drive erosion and sedimentation in river channels. Here, we show the direct impact of the supply of coarse-grained, hard, sediment on the geometry of bedrock channels from the Rangitikei river, New Zealand. Channels receiving a coarse bedload sediment supply are systematically (up to an order of magnitude) wider than channels with no bedload sediment input for a given discharge. We also present physical model experiments of a bedrock river channel with a fixed water discharge (1.5 l/min) under different Qs (between 0 and 20 g/l) that allow the quantification of the role of sediment in setting the width and slope of channels and the distribution of shear stress within channels. The addition of bedload sediment increases the width, slope, and width-to-depth ratio of the channels, and increasing sediment loads promote emerging complexity in channel morphology and shear stress distributions. Channels with low Qs are characterised by simple in-channel morphologies with a uniform distribution of shear stress within the channel while channels with high Qs are characterised by dynamic channels with multiple active threads and a non-uniform distribution of shear stress. We compare bedrock channel geometries from the Rangitikei and the experiments to alluvial channels and demonstrate that the behaviour is similar, with a transition from single thread and uniform channels to multiple threads occurring when bedload sediment is present. In the experimental bedrock channels, this threshold Qs is when the input sediment supply exceeds the transport capacity of the channel. Caution is required when using the channel geometry to reconstruct past environmental conditions or to invert for tectonic uplift rates, because multiple configurations of channel geometry can exist for a given discharge, solely due to input Qs.

Funding

European Union’s Horizon 2020 research and innovation programme through a Marie Sklodowska-Curie Actions Individual Fellowship (no. 703230, to E.B)

European Research Council (grant agreement no. 803721, to P.S)

EROQUAKE project funded by the Agence Nationale de la Recherche No. ANR-14-CE33-005 (to P.S).

History

School

  • Social Sciences and Humanities

Department

  • Geography and Environment

Published in

Earth Surface Processes and Landforms

Citation

Baynes, E.... et al. (2020). Sediment flux driven channel geometry adjustment of bedrock and mixed gravel‐bedrock rivers. Earth Surface Processes and Landforms, In Press.

Publisher

Wiley

Version

AM (Accepted Manuscript)

Publisher statement

This is the peer reviewed version of the following article: Baynes, E.... et al. (2020). Sediment flux driven channel geometry adjustment of bedrock and mixed gravel‐bedrock rivers. Earth Surface Processes and Landforms, In Press., which has been published in final form at https://doi.org/10.1002/esp.4996. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions

Acceptance date

31/08/2020

Publication date

2020-09-05

ISSN

0197-9337

eISSN

1096-9837

Language

en

Depositor

Dr Edwin Baynes Deposit date: 7 September 2020

Article number

esp.4996

Exports