How concave are river channels?

Abstract

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 k s . However, the calculation of channel steepness requires the normalisation of channel gradient by drainage area. This relationship be-5 tween 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 10 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 15 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.

Evidence of subsurface control on the coevolution of hillslope morphology and runoff generation

“…We conducted geomorphic analyses using a lidar-derived digital elevation model with 0.76 m resolution, which was collected in 2015 and is publicly available from Baltimore County. We conducted all topographic analyses using LSDTopoTools (S. Mudd et al, 2022). To determine hillslope length and relief, we began by identifying the channel networks at both sites using the DrEICH algorithm .…”

Image Texture as Quality Indicator for Optical DEM Generation: Geomorphic Applications in the Arid Central Andes

“…Curvature was calculated in a 3 × 3 pixel window using the free and open-source LSDTopoTools software [47] on all DEMs projected to UTM coordinates with 3 m resolution. Many options exist for curvature [48], but here we choose the tangential curvature as output by LSDTopoTools via a quadratic-fitting approach [49].…”

Cosmogenic (un-)steadiness revealed by paired-nuclide catchment-wide denudation rates in the formerly half-glaciated Vosges Mountains (NE France)

“…For each DEM pixel, slope was computed as the steepest gradient between the eight 164 neighbouring pixels, using the function terrain of the raster package in R (Hijmans, 2022). Normalised channel 165 steepness index (ksn) was computed using the LSD Topotools software (Mudd et al, 2018) with a reference 166 concavity of 0.45 for inter-catchment comparison (Fig. 1C).…”