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Impact of changing concavity indices on channel steepness and divide migration metrics

Gailleton, Boris and Mudd, Simon M. and Clubb, Fiona J. and Grieve, Stuart W.D. and Hurst, Martin D. (2021) 'Impact of changing concavity indices on channel steepness and divide migration metrics.', Journal of Geophysical Research: Earth Surface, 126 (10). e2020JF006060.


The concavity index, urn:x-wiley:21699003:media:jgrf21424:jgrf21424-math-0001, describes how quickly river channel gradient declines downstream. It is used in calculations of normalized channel steepness index, urn:x-wiley:21699003:media:jgrf21424:jgrf21424-math-0002, a metric for comparing the relative steepness of channels with different drainage area. It is also used in calculating a transformed longitudinal coordinate, urn:x-wiley:21699003:media:jgrf21424:jgrf21424-math-0003, which has been employed to search for migrating drainage divides. A urn:x-wiley:21699003:media:jgrf21424:jgrf21424-math-0004 value of 0.45 is typically assumed in studies. Here we quantify the variability in urn:x-wiley:21699003:media:jgrf21424:jgrf21424-math-0005 across multiple landscapes distributed across the globe. We describe the degree to which both the spatial distribution and magnitude of urn:x-wiley:21699003:media:jgrf21424:jgrf21424-math-0006 and urn:x-wiley:21699003:media:jgrf21424:jgrf21424-math-0007 can be distorted if urn:x-wiley:21699003:media:jgrf21424:jgrf21424-math-0008 is assumed rather than constrained. Differences between constrained and assumed urn:x-wiley:21699003:media:jgrf21424:jgrf21424-math-0009 of 0.1 or less are unlikely to affect the spatial distribution and relative magnitude of urn:x-wiley:21699003:media:jgrf21424:jgrf21424-math-0010 values, but larger differences can change the spatial distribution of urn:x-wiley:21699003:media:jgrf21424:jgrf21424-math-0011 and in extreme cases invert differences in relative steepness: relatively steep reaches can appear relatively gentle as quantified by urn:x-wiley:21699003:media:jgrf21424:jgrf21424-math-0012. These inversions are function of the range of drainage area in the considered watersheds. We also demonstrate that the urn:x-wiley:21699003:media:jgrf21424:jgrf21424-math-0013 coordinate, and therefore the detection of migrating drainage divides, is sensitive to varying values of urn:x-wiley:21699003:media:jgrf21424:jgrf21424-math-0014. The median of most likely urn:x-wiley:21699003:media:jgrf21424:jgrf21424-math-0015 across a wide range of mountainous and upland environments is 0.425. This wide range of variability suggests workers should not assume any value for urn:x-wiley:21699003:media:jgrf21424:jgrf21424-math-0016, but should instead calculate a representative urn:x-wiley:21699003:media:jgrf21424:jgrf21424-math-0017 for the landscape of interest, and exclude basins for which this value is a poor fit.

Item Type:Article
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Publisher statement:© 2021 The Authors. This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.
Date accepted:01 September 2021
Date deposited:06 January 2022
Date of first online publication:05 October 2021
Date first made open access:06 January 2022

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