Preprints
https://doi.org/10.5194/esurf-2021-40
https://doi.org/10.5194/esurf-2021-40

  25 May 2021

25 May 2021

Review status: a revised version of this preprint is currently under review for the journal ESurf.

Hilltop curvature as a proxy for erosion rate: Wavelets enable rapid computation and reveal systematic underestimation

William T. Struble1,2 and Joshua J. Roering2 William T. Struble and Joshua J. Roering
  • 1Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA
  • 2Department of Earth Sciences, University of Oregon, Eugene, Oregon, 97403, USA

Abstract. Estimation of erosion rate is an important component of landscape evolution studies, particularly in settings where transience or spatial variability in uplift or erosion generates diverse landform morphologies. While bedrock rivers are often used to constrain the timing and magnitude of changes in baselevel lowering, hilltop curvature (or convexity), CHT, provides an additional opportunity to map variations in erosion rate given that average slope angle becomes insensitive to erosion rate owing to threshold slope processes. CHT measurement techniques applied in prior studies (e.g. polynomial functions), however, tend to be computationally expensive when they rely on high resolution topographic data such as lidar, limiting the spatial extent of hillslope geomorphic studies to small study regions. Alternative techniques such as spectral tools like continuous wavelet transforms present an opportunity to rapidly document trends in hilltop convexity across expansive areas. Here, we demonstrate how continuous wavelet transforms (CWTs) can be used to calculate the Laplacian of elevation, which we utilize to estimate erosion rate in three catchments of the Oregon Coast Range that exhibit varying slope angle, slope length, and hilltop convexity, implying differential erosion. We observe that CHT values calculated with the CWT are similar to those obtained from 2D polynomial functions. Consistent with recent studies, we find that erosion rates estimated with CHT from both CWTs and 2D polynomial functions are consistent with erosion rates constrained with cosmogenic radionuclides from stream sediments. Importantly, our CWT approach calculates curvature 102–103 times more quickly than 2D polynomials. As such, continuous wavelet transforms provide a compelling approach to rapidly quantify regional variations in erosion rate as well as lithology, structure, and hillslope sediment transport processes, which are encoded in hillslope morphology. Finally, we test the accuracy of CWT and 2D polynomial techniques by constructing a series of synthetic hillslopes generated by a theoretical nonlinear transport model that exhibit a range of erosion rates and topographic noise characteristics. Notably, we find that neither CWTs nor 2D polynomials reproduce the theoretically prescribed CHT value for hillslopes experiencing moderate to fast erosion rates, even when no topographic noise is added. Rather, CHT is systematically underestimated, producing a power law relationship between erosion rate and CHT that can be attributed to artifacts from the increasing prominence of planar hillslopes that narrow the zone of hilltop convexity as erosion rate increases. As such, we recommend careful consideration of measurement length scale when applying CHT to estimate erosion rate in moderate to fast-eroding landscapes, where curvature measurement techniques may be prone to systematic underestimation.

William T. Struble and Joshua J. Roering

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on esurf-2021-40', Tyler Doane, 14 Jun 2021
  • RC2: 'Comment on esurf-2021-40', Anonymous Referee #2, 17 Jun 2021
  • AC1: 'Comment on esurf-2021-40 - Response to Reviewers', William Struble, 07 Jul 2021

William T. Struble and Joshua J. Roering

William T. Struble and Joshua J. Roering

Viewed

Total article views: 653 (including HTML, PDF, and XML)
HTML PDF XML Total Supplement BibTeX EndNote
499 145 9 653 20 3 4
  • HTML: 499
  • PDF: 145
  • XML: 9
  • Total: 653
  • Supplement: 20
  • BibTeX: 3
  • EndNote: 4
Views and downloads (calculated since 25 May 2021)
Cumulative views and downloads (calculated since 25 May 2021)

Viewed (geographical distribution)

Total article views: 546 (including HTML, PDF, and XML) Thereof 546 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 30 Jul 2021
Download
Short summary
We used a mathematical technique known as a wavelet transform to calculate the curvature of hilltops in western Oregon, which we used to estimate erosion rate. We find that this technique operates over than 100 times faster than other techniques and produces accurate erosion rates. We additionally built artificial hillslopes to test the accuracy of curvature measurement methods. We find that at fast erosion rates, curvature is underestimated, raising questions of measurement accuracy elsewhere.