Bumps in river profiles: uncertainty assessment and smoothing using quantile regression techniques

Dirk Scherler,Wolfgang Schwanghart

doi:10.5194/esurf-5-821-2017

Abstract

Abstract. The analysis of longitudinal river profiles is an important tool for studying landscape evolution. However, characterizing river profiles based on digital elevation models (DEMs) suffers from errors and artifacts that particularly prevail along valley bottoms. The aim of this study is to characterize uncertainties that arise from the analysis of river profiles derived from different, near-globally available DEMs. We devised new algorithms – quantile carving and the CRS algorithm – that rely on quantile regression to enable hydrological correction and the uncertainty quantification of river profiles. We find that globally available DEMs commonly overestimate river elevations in steep topography. The distributions of elevation errors become increasingly wider and right skewed if adjacent hillslope gradients are steep. Our analysis indicates that the AW3D DEM has the highest precision and lowest bias for the analysis of river profiles in mountainous topography. The new 12 m resolution TanDEM-X DEM has a very low precision, most likely due to the combined effect of steep valley walls and the presence of water surfaces in valley bottoms. Compared to the conventional approaches of carving and filling, we find that our new approach is able to reduce the elevation bias and errors in longitudinal river profiles.

Highlights

Rivers play a dominant role in the topographic evolution of the Earth surface and possibly other planetary bodies (Hack, 1957; Howard, 1998; Whipple et al, 2013)
We addressed the first point by comparing river profiles obtained from global digital elevation models (DEMs) (SRTM-1, ALOS World 3D30 (AW3D), ASTER GDEM v2, TanDEM-X DEM; see Table 1, Fig. 4)
A comparison of longitudinal river profiles derived from coarse-resolution globally available DEMs and lidar data shows that DEMs commonly overestimate elevations along rivers in steep topography

Summary

Introduction

Rivers play a dominant role in the topographic evolution of the Earth surface and possibly other planetary bodies (Hack, 1957; Howard, 1998; Whipple et al, 2013) They transfer sediment from mountains to depositional basins, set the base level for hillslopes, and convey tectonic and climatic signals across landscapes. For example, reflect spatial variations in uplift rates (Whipple et al, 2013; Mudd et al, 2014; Scherler et al, 2014) and indicate the extent of past glaciations (Brardinoni and Hassan, 2006). Longitudinal river profiles and metrics derived from them (e.g., the normalized channel steepness metric ksn; Wobus et al, 2006) have become important tools for studying the topographic evolution of mountain belts and deciphering changes in climate and tectonics (Bishop et al, 2005)

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Conclusion