Reshaping the Critical Zone with Hydrogeodesy

Abstract : This document summarizes the research activities I have been leading during the last eight years within Geosciences Rennes and the "Environmental Dynamics" team. The developments undertaken are rooted in my doctoral work (Longuevergne, 2008) ; they have evolved at the rhythm of reflections and experiences, meetings and discussions. They have been enhanced by close team-wide interactions in Rennes, and collaborations with several researchers in France, Europe and all over the world. The originality of the research I have conducted owes a lot to constructive interferences with researchers from other disciplines, but also from a focused work specific topics. The main contribution lies on the development and qualification of geodetic instruments as tools for hydrology, mainly driven by an instrumental and experimental approach. The first chapter introduces the concept of the Critical Zone, which is reinterpreted as a dynamic notion to better include the full role of groundwater within the water cycle on a wide range of temporal scales. As water is in permanent contact with rock, I also underline the physical interactions between the "Critical Zone" and the "Solid Earth", suggesting the opportunity to fertilize the reciprocal input of both discipline. Among the Solid Earth tools, geodesy offers a wide range of highly accurate instruments, stable and well calibrated, which can be used to capture the spatio-temporal redistribution of water in the subsurface, from surface and space-borne observations. The second chapter explores their ability to estimate water storage and pressure changes and bring insights into the heterogeneous, and hidden Critical Zone. Quantifying water transfers in the Earth’s subsurface is motivated by basic scientific questions and major challenges, such as the management of (water) resources, the exploitation and storage of resources and energy, the sensitivity of the subsurface to deformation, the understanding of the links between the external and internal envelopes of the Earth. Then, the future challenges I want to explore are described in the third chaper, namely (1) the non-linear nature of fracture flow and transfer processes ; (2) the imaging of subsurface flow and their control by heterogeneities ; (3) the full representation of the groundwater role in the Earth’s climatic system ; and (4) the inter-relationship between the different compartments composing ecosystems, through a large-scale experiment.
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Habilitation à diriger des recherches
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Laurent Longuevergne. Reshaping the Critical Zone with Hydrogeodesy. Earth Sciences. Université de rennes 1, 2018. ⟨tel-02373443⟩

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