How long is a hillslope?

Grieve, S. W.D., Mudd, S. M. and Hurst, M. D. (2016) How long is a hillslope? Earth Surface Processes and Landforms, 41(8), pp. 1039-1054. (doi: 10.1002/esp.3884)

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Hillslope length is a fundamental attribute of landscapes, intrinsically linked to drainage density, landslide hazard, biogeochemical cycling and hillslope sediment transport. Existing methods to estimate catchment average hillslope lengths include inversion of drainage density or identification of a break in slope–area scaling, where the hillslope domain transitions into the fluvial domain. Here we implement a technique which models flow from point sources on hilltops across pixels in a digital elevation model (DEM), based on flow directions calculated using pixel aspect, until reaching the channel network, defined using recently developed channel extraction algorithms. Through comparisons between these measurement techniques, we show that estimating hillslope length from plots of topographic slope versus drainage area, or by inverting measures of drainage density, systematically underestimates hillslope length. In addition, hillslope lengths estimated by slope–area scaling breaks show large variations between catchments of similar morphology and area. We then use hillslope length–relief structure of landscapes to explore nature of sediment flux operating on a landscape. Distinct topographic forms are predicted for end-member sediment flux laws which constrain sediment transport on hillslopes as being linearly or nonlinearly dependent on hillslope gradient. Because our method extracts hillslope profiles originating from every ridgetop pixel in a DEM, we show that the resulting population of hillslope length–relief measurements can be used to differentiate between linear and nonlinear sediment transport laws in soil mantled landscapes. We find that across a broad range of sites across the continental United States, topography is consistent with a sediment flux law in which transport is nonlinearly proportional to topographic gradient.

Item Type:Articles
Additional Information:This work wassupported by NERC grant NE/J009970/1 and US Army Research Officecontract number W911NF-13-1-0478. This paper is published with thepermission of the Executive Director of the British Geological Surveyand was supported in part by the Climate and Landscape Change re-search programme at the BGS.
Keywords:Sediment flux, topographic analysis, hillslopes, length scales.
Glasgow Author(s) Enlighten ID:Hurst, Dr Martin
Authors: Grieve, S. W.D., Mudd, S. M., and Hurst, M. D.
Subjects:G Geography. Anthropology. Recreation > G Geography (General)
G Geography. Anthropology. Recreation > GA Mathematical geography. Cartography
G Geography. Anthropology. Recreation > GB Physical geography
Q Science > QE Geology
College/School:College of Science and Engineering > School of Geographical and Earth Sciences
Journal Name:Earth Surface Processes and Landforms
Publisher:John Wiley and Sons
ISSN (Online):1096-9837
Published Online:11 January 2016
Copyright Holders:Copyright © 2016 The Authors
First Published:First published in Earth Surface Processes and Landforms 41(8):1039-1054
Publisher Policy:Reproduced under a Creative Commons License

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