EGUsphere EGUsphere EGUsphere EGUsphere Copernicus Publications Göttingen, Germany 10.5194/egusphere-2026-1018 Alluvial river-channel width: transient adjustment and dynamic equilibrium Wickert Andrew D. https://orcid.org/0000-0002-9545-3365 1 2 3 Jones Jabari C. https://orcid.org/0000-0002-9809-285X 1 2 4 Libby Devon 5 Larson Phillip H. 5 Barnhart Katherine R. https://orcid.org/0000-0001-5682-455X 6 7 11 Van Wyk de Vries Maximillian S. https://orcid.org/0000-0001-7752-8813 1 2 8 9 Schildgen Taylor F. https://orcid.org/0000-0002-4236-4609 3 10 Saint Anthony Falls Laboratory, University of Minnesota, Minneapolis, MN 55414, USA Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN 55455, USA Sektion 4.6: Geomorphologie, GFZ Helmholtz-Zentrum für Geoforschung, Potsdam, 14473, Germany Department of Earth and Oceanographic Science, Bowdoin College, Brunswick, ME 04011, USA EARTH Systems Laboratory, Minnesota State University, Mankato, MN 56001, USA Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, USA Department of Geological Sciences, University of Colorado, Boulder, CO 80309, USA Department of Geography, University of Cambridge, Cambridge, CB2 3EL, UK Department of Earth Sciences, University of Cambridge, Cambridge, CB3 0EZ, UK Institut für Geowissenschaften, Universität Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam, Germany now at: U.S. Geological Survey, Geologic Hazards Science Center, Golden, CO 80401, USA 06 03 2026 2026 1 52 Copyright: © 2026 Andrew D. Wickert et al. 2026 This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/ This article is available from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-1018/ The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-1018/egusphere-2026-1018.pdf

Alluvial river channels naturally widen and narrow as large floods scour banks and smaller ones supply sediments that help build bars and channel margins. Despite substantial advances into the controls on the equilibrium width of river channels, relatively little theory underpins our knowledge on transient river-channel-width evolution. Such a knowledge gap inhibits us from predicting the impacts of present-day nonstationary hydrology on river-channel stability and geomorphic change. Here we present a unified approach to model transient channel widening, via erosion of cohesive banks and mobilization of noncohesive clasts, and narrowing, via lateral diffusion of sediment that attaches to the banks. The resultant model can take a full hydrograph as input, allowing the hydraulic geometry and associated "geomorphically effective" water discharge to emerge dynamically. Stable widths develop via the inverse relationship between channel width and flow depth, and therefore, shear stress on the channel margins. Equilibrium solutions closely approximate data and theory on channels with both gravel and mud banks, and we compare transient solutions to the rapidly widening Minnesota and Cannon Rivers (Minnesota, USA) and the narrowing Green River and Diamond Fork (Utah, USA). Documented Python source code to run these computations is available from GitHub and Zenodo via the "OTTAR" package, and may be installed via pip from PyPI.

 Alexander von Humboldt-Stiftung Humboldt-Forschungsstipendium National Science Foundation 944782 1725774 College of Science and Engineering, University of Minnesota Graduate-student Fellowship Graduate School, University of Minnesota DOVE Fellowship Minnesota Department of Natural Resources Lessard-Sams Outdoor Heritage Council