Preprints
https://doi.org/10.5194/esurf-2021-83
https://doi.org/10.5194/esurf-2021-83

  09 Nov 2021

09 Nov 2021

Review status: this preprint is currently under review for the journal ESurf.

Investigation of stochastic-threshold incision models across a climatic and morphological gradient

Clément Desormeaux1, Vincent Godard1,2, Dimitri Lague3, Guillaume Duclaux4, Jules Fleury1, Lucilla Benedetti1, Olivier Bellier1, and the ASTER Team Clément Desormeaux et al.
  • 1Aix-Marseille Univ, CNRS, IRD, INRAE, Coll France, CEREGE, 13100 Aix-en-Provence, France
  • 2Institut Universitaire de France (IUF), Paris, France
  • 3Univ Rennes, CNRS, Géosciences Rennes, UMR 6118, 35000 Rennes, France
  • 4Université Côte d’Azur, CNRS, Observatoire de la Côte d’Azur, IRD, Géoazur, 250 rue Albert Einstein, Sophia Antipolis 06560 Valbonne, France
  • A full list of authors appears at the end of the paper.

Abstract. Long-term landscape evolution is controlled by tectonic and climatic forcing acting through surfaces processes. Rivers are the main drivers of continental denudation because they set the base level of most hillslopes and the mechanisms of fluvial incision are a key focus in geomorphological research and require accurate representation and models. River incision is often modeled with the Stream Power Model (SPM), based on the along-stream evolution of drainage area and channel elevation gradient, but can also incorporate more complex processes such as threshold effects and statistical discharge dis-tributions, which are fundamental features of river dynamics. Despite their importance in quantitative geomorphology, such model formulations have been confronted with fields data only in a limited number of cases. Here we investigate the behavior of stochastic-threshold incision models across the south-eastern margin of the Massif Central in France which is characterized by significant relief and the regular occurrence of high-discharge events. Our study is based on a new dedicated dataset combining measurements of discharge variability from gauging stations, denudation rates on 34 basins from 10Be cosmogenic radionuclide (CRN) concentration measurements in river sediments, morphometric analysis of river long-profiles analysis and field observations. This new dataset is used for a systematic investigation of various formulations of the SPM and discuss the importance of incision thresholds. Denudation rates across the SE margin of the Massif Central are in the 20–120 mm/ka range and they positively correlate with slope and precipitations. However, the relationship with steepness index is complex and hints at the importance of taking into account the spatial variations in parameters controlling the SPM. Overall, the range of denudation rate across the margin can mainly be explained using a simple version of the SPM accounting for spatially heterogeneous runoff. More complex formulations including stochastic discharge and incision thresholds yield poorer performances unless spatial variations in bedload characteristics, controlling incision threshold, are taken into account. Our results highlight the importance of the hypotheses used on such threshold in SPM application to field studies and notably the impact of actual constraints on bedload size.

Clément Desormeaux et al.

Status: open (until 02 Jan 2022)

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Clément Desormeaux et al.

Clément Desormeaux et al.

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Short summary
Landscape evolution is highly dependent on climatic parameters and the occurrence of intense precipitation events is considered to be an important driver of river incision. We compare the rate of erosion with the variability of river discharge in a mountainous landscape of SE France where high magnitude floods regularly occurs. Our study highlights the importance of the hypotheses made on the threshold that river discharge need to exceed in order to effectively cut down into the bedrock.