Impact de la végétation sur l'érosion de bassins versants marneux

Abstract : While it is well-recognized that vegetation can affect erosion, sediment yield, andover longer time scales landform evolution, the nature of this interaction and how it should be modeled is not obvious and may depend on the study site. Understanding the modes of action of vegetation is crucial to interpret the current forms of the landscape and to reconstruct the history of erosion on one hand, and to predict the erosive and morphological dynamics of these systems in a global climate change context on the other hand. The aim of the thesis is to identify the nature and the magnitude of the vegetation impact on erosion in a context of marly catchments of the Draix-Bléone Observatory. We worked on two catchments of the Observatory withsimilar size and lithology but with a contrasting vegetation cover : Laval basin, mainly bare, and Brusquet basin, entirely reforested at the end of the 19th century as part of restoration work undertaken on the Alpes-de-Haute-Provence. Firstly, we carried out a morphometric analysis in order to investigate the links between indicators characterizing the basin morphology and vegetation. The analysis underlines a strong link between vegetation and slope. Secondly, so as to account for this strong coupling between vegetation, topography and erosion, we built a landscape evolution model with Landlab library and we introduced the effect of vegetation into this model. We used a leave-one-out" calibration and cross-validation procedure in order to calibrate and test simultaneously the predictive efficiency of the model. The model was forced with runoff timeseries observed on the two watersheds. Results from the simulations show that hillslope transport processes highly depend on vegetation cover, while transport processes in the fluvial network do not appear to be affected by the presence of vegetation. In addition, the model sheds a new light by demonstrating that, at this study site, vegetation acts on erosion mostly by reducing soil erodibility, thus increasing its cohesion, rather than by reducing surface runoff. Finally, the model and the methodology we propose in this thesis work, are a useful tool first, to quantify and evaluate the efficiency of previous revegetation/reforestation operations, and secondly, to provide guidances for future restoration work.
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Submitted on : Tuesday, August 27, 2019 - 9:10:08 AM
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Alexandra Carriere. Impact de la végétation sur l'érosion de bassins versants marneux. Géologie appliquée. Université Grenoble Alpes, 2019. Français. ⟨NNT : 2019GREAU012⟩. ⟨tel-02271551⟩



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