Preprints
https://doi.org/10.5194/esurf-2021-82
https://doi.org/10.5194/esurf-2021-82

  24 Nov 2021

24 Nov 2021

Review status: this preprint is currently under review for the journal ESurf.

The push and pull of abandoned channels: How floodplain processes and healing affect avulsion dynamics and alluvial landscape evolution in foreland basins

Harrison K. Martin and Douglas A. Edmonds Harrison K. Martin and Douglas A. Edmonds
  • Department of Earth and Atmospheric Sciences, Indiana University, Bloomington, Indiana, 47408, United States of America

Abstract. River avulsions are an important mechanism by which sediment is routed and emplaced in foreland basins. However, because avulsions occur infrequently, we lack observational data that might inform where, when, and why avulsions occur and these questions are instead often investigated by rule-based numerical models. These models have historically simplified or neglected the effects of abandoned channels on avulsion dynamics, even though fluvial megafans in foreland basins are characteristically covered in abandoned channels. Here, we investigate the pervasiveness of abandoned channels on modern fluvial megafan surfaces. Then, we present a physically based cellular model that parameterizes interactions between a single avulsing river and abandoned channels in a foreland basin setting. We investigate how abandoned channels affect avulsion set-up, pathfinding, and landscape evolution. We demonstrate and discuss how the processes of abandoned channel inheritance and transient knickpoint propagation post-avulsion serve to shortcut the time necessary to set-up successive avulsions. Then, we address the idea that abandoned channels can both repel and attract future pathfinding flows under different conditions. By measuring the distance between the mountain-front and each avulsion over long (106 to 107 years) timescales, we show that increasing abandoned channel repulsion serves to push avulsions farther from the mountain-front, while increasing attraction pulls avulsions proximally. Abandoned channels do not persist forever, and we test possible channel healing scenarios (deposition-only, erosion-only, and far-field directed) and show that only the final scenario achieves dynamic equilibrium without completely filling accommodation space. We also observe megafan growth occurring via ~O:105 year lobe switching, but only in our runs that employ deposition-only or erosion-only healing modes. Finally, we highlight opportunities for future field work and remote sensing efforts to inform our understanding of the role that floodplain topography, including abandoned channels, plays on avulsion dynamics.

Harrison K. Martin and Douglas A. Edmonds

Status: open (until 09 Jan 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Harrison K. Martin and Douglas A. Edmonds

Model code and software

RiverWalk-AM v1.0.0 Harrison Martin, Doug Edmonds https://doi.org/10.5281/zenodo.5576789

Video supplement

Martin and Edmonds Avulsion Model Supplemental Videos 1-3 Harrison Martin and Doug Edmonds https://doi.org/10.5446/54887

Harrison K. Martin and Douglas A. Edmonds

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Short summary
River avulsions (rivers suddenly changing course) redirect water and sediment. These floods can harm people and control how some landscapes evolve. We model how abandoned channels from older avulsions affect where, when, and why future avulsions occur in mountain-front areas. We show that abandoned channels can push and pull avulsions, and the way they heal controls landscapes. Avulsion models should include abandoned channels; we also highlight opportunities for future field workers.