Human activities disrupt the hydrosedimentary regime of most rivers. Retrospective studies and monitoring of the state of rivers are carried out by several disciplines. The number of forcings to which these natural environments are subjected has risen sharply since the Industrial Revolution. Among these anthropogenic forcings, the construction of hydroelectric power plants undoubtedly has the most significant impact on the river corridor. The installation of these transverse structures can be accompanied by the diversion of flows to the hydroelectric power station with an engineered channel. On the Rhone River, numerous sections of the river have been by-passed and it has been observed that sediment deposits are characterized by a clear granulometric break following this installation. Parts of the river floodplains are home to these deposits, which constitute a sedimentation archive. These include secondary branches and river annexes. The evolution of hydraulic and sedimentary dynamics, in relation to hydraulic forcing, should enable us to characterize this evolution. This work focuses on the pressures exerted on the sediment deposition zones constituted by the secondary branches. The Rhone River is a French and Swiss river subject to strong anthropogenic pressures; it is the case study of this thesis. In parallel with field investigations to characterize these deposits, we built a model of these secondary channels to simulate their hydraulic and sedimentary dynamics. The numerical results enable us to understand this sedimentation in relation to hydraulic events. Our results show that flood intensity and duration generate a sediment response that correlates neither with flood intensity or duration. These results are also coupled with in natura observations, allowing us to evolve the conception and temporal representation of fluvial sedimentary deposits. This thesis also aims to use the model to quantify the role of anthropogenic forcings on the dynamics of secondary arms, and to extend the reconstruction of deposits to unknown areas. Finally, cross-referencing local field observations with simulation results will enable us to obtain a better spatio-temporal resolution of hydrosedimentary dynamics.

Funding

ENTPE

Cite the thesis

Nicolas Noclin. Rôle du forçage hydraulique sur les environnements de dépôt sédimentaire des annexes fluviales : approche sédimentologique et numérique appliquée au Rhône. Sciences de la Terre. École Nationale des Travaux Publics de l'État [ENTPE], 2024. Français. ⟨NNT : 2024ENTP0001⟩. ⟨tel-04695873⟩

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