How concave are river channels?

Mudd, S. M., Clubb, F. J., Gailleton, B. and Hurst, M. D. (2018) How concave are river channels? Earth Surface Dynamics, 6(2), pp. 505-523. (doi: 10.5194/esurf-6-505-2018)

Abstract

For over a century geomorphologists have attempted to unravel information about landscape evolution, and processes that drive it, using river profiles. Many studies have combined new topographic datasets with theoretical models of channel incision to infer erosion rates, identify rock types with different resistance to erosion, and detect potential regions of tectonic activity. The most common metric used to analyse river profile geometry is channel steepness, or ks. However, the calculation of channel steepness requires the normalisation of channel gradient by drainage area. This relationship between channel gradient and drainage area is referred to as channel concavity, and despite being crucial in determining channel steepness, is challenging to constrain. In this contribution we compare both slope–area methods for calculating concavity and methods based on integrating drainage area along the length of the channel, using so-called chi'' (χ) analysis. We present a new χ-based method which directly compares χ values of tributary nodes to those on the main stem: this method allows us to constrain channel concavity in transient landscapes without assuming a linear relationship between χ and elevation. Patterns of channel concavity have been linked to the ratio of the area and slope exponents of the stream power incision model (m/n): we therefore construct simple numerical models obeying detachment-limited stream power and test the different methods against simulations with imposed m and n. We find that χ-based methods are better than slope–area methods at reproducing imposed m/n ratios when our numerical landscapes are subject to either transient uplift or spatially varying uplift and fluvial erodibility. We also test our methods on several real landscapes, including sites with both lithological and structural heterogeneity, to provide examples of the methods' performance and limitations. These methods are made available in a new software package so that other workers can explore how concavity varies across diverse landscapes, with the aim to improve our understanding of the physics behind bedrock channel incision.

• Item Type: Articles
• Additional Information: This work was supported by Natural Environment Research Council grants NE/J009970/1 to Mudd, NE/P012922/1 to Clubb. Gailleton was funded by European Union Initial Training Grant 674899 — SUBITOP.
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Hurst, Dr Martin
• Authors: Mudd, S. M., Clubb, F. J., Gailleton, B., and Hurst, M. D.
• College/School: College of Science and Engineering > School of Geographical and Earth Sciences
• Journal Name: Earth Surface Dynamics
• Publisher: Copernicus Publications
• ISSN: 2196-6338
• ISSN (Online): 2196-6338
• Published Online: 05 February 2018
• Copyright Holders: Copyright © 2018 The Authors
• First Published: First published in Earth Surface Dynamics Discussions 6(2):505-523
• Publisher Policy: Reproduced under a Creative Commons License