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Lookup NU author(s): Dr Christopher HackneyORCiD
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
© 2025. The Author(s). The surface roughness of river beds affects flow resistance and sediment transport. In rough-bed rivers (RBRs), where flow is shallow relative to roughness height, the surface roughness is difficult to define due to complex multi-scale roughness elements (bedrock, boulders, and sediment patches). Here, neither the sediment grain size distribution percentiles (e.g., (Formula presented.)) nor the bed elevation standard deviation (Formula presented.) fully captures the surface roughness. This paper uses high-resolution digital elevation models of 20 RBR reaches to evaluate their channel morphology and surface roughness. A set of 29 different multi-scale elevation, gradient-based, and area-based, roughness metrics are assessed. Correlation analysis and robust feature selection identified interchangeable metrics, revealing which roughness metrics provided independent information on channel characteristics. Principal component analysis and hierarchical clustering analysis showed that a comprehensive description of RBR topography requires the concurrent use of multiple metrics encompassing (a) a vertical or horizontal scale-based roughness metric, (b) a slope- or area-based metric, and (c) surface elevation skewness or kurtosis. Slope- and area-based metrics can include roughness directionality relative to the bulk flow. We demonstrate how surface roughness metrics, specifically the use of multiple metrics in unison, are suitably capable of representing and distinguishing between RBRs with differing characteristics. In some cases, rivers with different morphology types (e.g., boulder bed or bedrock) are found to have greater similarity in their surface roughness metrics than rivers classified as morphologically similar. We then discuss RBR morphological and roughness characteristics in the context of flow resistance and sediment transport processes.
Author(s): Houseago RC, Hodge RA, Asher B, Ferguson RI, Hackney CR, Hardy RJ, Hoey TB, Johnson JPL, Rice SP, Yager EM, Yamasaki T
Publication type: Article
Publication status: Published
Journal: Journal of Geophysical Research: Earth Surface
Year: 2025
Volume: 130
Issue: 5
Online publication date: 16/05/2025
Acceptance date: 09/04/2025
Date deposited: 22/04/2025
ISSN (print): 2169-9003
ISSN (electronic): 2169-9011
Publisher: John Wiley and Sons Inc.
URL: https://doi.org/10.1029/2024JF007996
DOI: 10.1029/2024JF007996
Data Access Statement: The data used in this paper is available via https://doi.org/10.5281/zenodo.14605934 (Houseago et al., 2024).
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