The influence of hillslope processes on large-scale landform evolution
Geophysics
Physical Geography
Final Report Abstract
Focus of this project was on the interaction between large-scale landform evolution and hillslope processes. Since the diffusion equation is still the most widely used model for erosion and sediment transport at hillslopes, it was planned to be the starting point. It was already known from previous studies that the diffusion model causes scaling problems in combination with fluvial models in which rivers are treated as linear objects. Results become dependent on the spatial resolution of the model. The hypothesis that the scaling problems can be solved by taking into account the sediment flux from hillslopes into rivers adequately did not hold. It was found that the flow pattern in the domain where neither fluvial nor hillslope processes dominate clearly is a fundamental problem. Overcoming the scaling issue required the development of an alternative model for erosion and sediment transport at hillslopes. As a central point, the new approach separates the topography into channel sites and hillslope sites and uses different models for erosion and sediment transport for channels and hillslopes. In contrast to previous approaches that also considered channels and hillslopes separately, the new model allows for a self-organization of channels and hillslopes. The new approach avoids the scaling issues of the established diffusion model. However, it also predicts different hillslope topographies. The diffusion model predicts convex hillslopes under spatially uniform erosion, while straight hillslope profiles require specific nonlinear diffusion models. In contrast, straight profiles are the preferred state in the new model under a wide range of conditions. Simple relations for the relief of catchments and for the drainage density (river length per area) could be derived. As a first specific application, a model for the formation of faceted topographies at normal faults was developed. Beyond the implementation of the new model for erosion and sediment transport at hillslopes, the development of the open-source landform evolution model OpenLEM was advanced. Considering layers with different properties, including the conversion of material by weathering, was one major development. Technically more challenging, a new scheme for simulating the deposition of sediment in lakes was developed. Furthermore, a Python class was developed, which makes all components of OpenLEM accessible from Python programs. This development will hopefully reduce the barrier of programming in C++ for potential users.
Publications
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The erosion and lifetime of impact craters on Earth, Mid-European Geomorphology Meeting 2022
Pietrek, A. & Hergarten, S.
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Self-organization of channels and hillslopes in models of fluvial landform evolution and its potential for solving scaling issues. Earth Surface Dynamics, 11(4), 741-755.
Hergarten, Stefan & Pietrek, Alexa
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A simple model for faceted topographies at normal faults based on an extended stream-power law. Earth Surface Dynamics, 12(6), 1315-1327.
Hergarten, Stefan
