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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union

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Earth Surf. Dynam., 5, 311-330, 2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
20 Jun 2017
A probabilistic framework for the cover effect in bedrock erosion
Jens M. Turowski1 and Rebecca Hodge2 1Helmholtzzentrum Potsdam, German Research Centre for Geosciences GFZ, Telegrafenberg, 14473 Potsdam, Germany
2Department of Geography, Durham University, Durham, DH1 3LE, UK
Abstract. The cover effect in fluvial bedrock erosion is a major control on bedrock channel morphology and long-term channel dynamics. Here, we suggest a probabilistic framework for the description of the cover effect that can be applied to field, laboratory, and modelling data and thus allows the comparison of results from different sources. The framework describes the formation of sediment cover as a function of the probability of sediment being deposited on already alluviated areas of the bed. We define benchmark cases and suggest physical interpretations of deviations from these benchmarks. Furthermore, we develop a reach-scale model for sediment transfer in a bedrock channel and use it to clarify the relations between the sediment mass residing on the bed, the exposed bedrock fraction, and the transport stage. We derive system timescales and investigate cover response to cyclic perturbations. The model predicts that bedrock channels can achieve grade in steady state by adjusting bed cover. Thus, bedrock channels have at least two characteristic timescales of response. Over short timescales, the degree of bed cover is adjusted such that the supplied sediment load can just be transported, while over long timescales, channel morphology evolves such that the bedrock incision rate matches the tectonic uplift or base-level lowering rate.

Citation: Turowski, J. M. and Hodge, R.: A probabilistic framework for the cover effect in bedrock erosion, Earth Surf. Dynam., 5, 311-330,, 2017.
Publications Copernicus
Short summary
Bedrock incision by rivers is driven by the impacts of sediment particles moved by the water flow. Sediment residing on the bed can protect the rock from impacts, thereby reducing erosion rates, a phenomenon known as the cover effect. The cover effect has been shown to be important in many field and laboratory experiments. Here, we develop a mathematical framework to describe the cover effect which can be used to compare data and to predict the extent of cover in streams.
Bedrock incision by rivers is driven by the impacts of sediment particles moved by the water...