Channel network source representation using digital elevation models

TLDR

The authors examine methods for determining hillslope size and channel network extent from DEMs and propose that an inflection in the drainage area–slope relationship marks a transition from debris‑flow dominated to alluvial channels. They evaluate several approaches for estimating the proportionality constant linking drainage area and slope that controls channel initiation, recommending that even limited field data be collected to calibrate this threshold. The study finds that a constant critical support area best delineates the hillslope/valley transition, while a slope‑dependent critical support area more accurately defines channel networks in soil‑mantled landscapes, and that high‑resolution DEMs with finer than 30 m grids are necessary to resolve steep topography.

Abstract

Methods for identifying the size, or scale, of hillslopes and the extent of channel networks from digital elevation models (DEMs) are examined critically. We show that a constant critical support area, the method most commonly used at present for channel network extraction from DEMs, is more appropriate for depicting the hillslope/valley transition than for identifying channel heads. Analysis of high‐resolution DEMs confirms that a constant contributing area per unit contour length defines the extent of divergent topography, or the hillslope scale, although there is considerable variance about the average value. In even moderately steep topography, however, a DEM resolution finer than the typical 30 m by 30 m grid size is required to accurately resolve the hillslope/valley transition. For many soil‐mantled landscapes, a slope‐dependent critical support area is both theoretically and empirically more appropriate for defining the extent of channel networks. Implementing this method for overland flow erosion requires knowledge of an appropriate proportionality constant for the drainage area‐slope threshold controlling channel initiation. Several methods for estimating this constant from DEM data are examined, but acquisition of even limited field data is recommended. Finally, the hypothesis is proposed that an inflection in the drainage area‐slope relation for mountain drainage basins reflects a transition from steep debris flow‐dominated channels to lower‐gradient alluvial channels.