Groundwater (GW) systems exist in dynamic balance with the climate and human pressure, connecting interfacing zones of recharge and discharge with multiple feedbacks. Quantifying the aquifer recharge and the stream-aquifer is a key issue for hydrogeologists to consider the safe yield and good water quality, especially in view of the ongoing changes in climate and land use. The objective of GWSBOUND is to provide monitoring and predictive tools of the water fluxes through these interfaces by the combined uses of hydrogeology, poroelasticity, petrophysics and geophysics approaches. The fully combined hydrogeophysics tools will improve the accuracy of groundwater models, aid in uncertainty assessment of its parameters by the uses of advanced numerical modelling, probabilistic, deep learning inversion approaches and spatiotemporal interpolation using the geostatistical approaches. The great novelty resides in the use of geophysical and hydrogeological data that are directly dependent on the water content storage, temperature and water level temporal variations. GWSBOUND will proceed in five main steps: developing a High-Performance numerical model to couple the groundwater and geophysical model through poroelastic and petrophysic models, create synthetic cases to realise a sensitivity analysis of the different heterogeneity configuration and hydrogeological regime on the hydrothermal and seismic wave responses, develop the workflow of the combined hydrogeological and geophysical inversion, apply this tool to the outlet of the Orgeval Critical Zone Observatory in current climatic conditions, and finally simulate the responses of the water resources to various IPCC scenarios of climate change (CMIP6 projections). The Orgeval Critical Zone Observatory (CZO) represents an opportunity to apply the combined inversion, for which an important database exists thanks to the French research program PIREN-Seine and the OZCAR research infrastructure.

The similarity between faulted geothermal reservoirs and hydrothermal ore deposits which exhibit similar features of behavior and fault activation suggests that a fundamental knowledge and better insight into the natural processes underlying the heat and mineral resources availability can be reached from a cross-analysis of these two systems. Both systems are characterized by hydrothermal pulses (cyclical increases in brine flowrate and temperature) which could correspond to modifications of the crustal stress regime marked by highly localized deformation and permeability enhancement of the geological systems. Current understanding suggest that only repeated fluid pulses in structurally-favorable contexts lead to the accumulation of giant ore deposits and could also emphasize the geothermal potential in similar contexts. The EARTH-BEAT project aims at untangling the relative importance of the geological structures, the brine thermodynamics and the regional stress regime in this phenomenon from geological observations, quantitative analysis and numerical modeling and, in a wider way, should give better insights on the key parameters controlling fault reactivation and their potential link with giant ore deposits formation and geothermal potential. It relies on several thermo-hydro-mechanical (THM) and reactive transport modeling approaches performed from the scale of fault gouge and damage zone up to the deposit scale. Laboratory tests will be first conducted to assess petrophysical and THM properties of faults and rocks used in models. Then, we will investigate the dynamics of a fault system, with different degrees of complexity, ultimately representative of an ore deposit in the Athabasca basin context. In parallel, reactive transfer simulations will be carried out to identify dissolution and precipitation localization. Confrontation with field observations will be performed by testing numerical modeling on real 3D geometries of unconformity related deposits.

The disadvantages of soil sealing in the city (flooding linked to rainwater runoff, wellbeing of people living in urban heat islands) are exacerbated by climate change. Desealing is therefore a necessity. However, it must take into account its own disadvantages such as the release of pollutants. Desealing, as a step of the renaturation process, is one answer to the European ‘no net land take’ objective by 2050, adopted by the French Climate and Resilience Act in 2021. Estimated currently around 100 M€/year, the French desealing market is expected to grow over the short to medium terms. However, local authorities, lack tools and methodologies, eg. for defining territorial and local desealing strategies. In this frame, the Permépolis project ambitions to develop a methodology to build territorial co-constructed desealing strategies. The current desealing operations aim to restore the water cycle, improve the resilience of cities to climate change and/or limit the artificialization of soils. Considering the different regulations (e.g. urban planning and environment), the various benefits and risks associated to desealing, and the different points of view of the stakeholders, the PerméPolis project identifies the following issue: How to combine, in a framework co-constructed with stakeholders, the relevant technical, legal and social information, in order to converge towards an efficient strategy for the desealing of soils in urbanized areas? The project associates, in an interdisciplinary approach, public research institutes (University G. Eiffel, Nantes University, MinesParis-PSL, UTC, ESGT, ONERA, BRGM, Cerema), a private partner (OTEIS) and a local authority (Nantes Metropolis). The consortium will address more particularly the following research questions: i) How to better characterize sealed soil properties at territorial scale? The consortium aims at improving hyperspectral data acquisition and treatment to map the nature and properties of sealed surfaces (materials, albedo, use frequency…) and to map the land and legal constraints affecting soils; ii) How to better characterize the benefits and risks associated with soil desealing? The project aims at assessing the effects of desealing on water runoff flooding and thermal comfort as well as on potential pollutant release ; iii) How to co-construct a territorial and local desealing strategy? The consortium aims to develop a method and to demonstrate its replicability on several territories, taking into account their specificities, the divergence factors (stakeholder points of view, regulations, legal constraints) as well as uncertainties. The main expected result is a method to co-construct optimized desealing strategies with stakeholders. It will include: i) a multi-criteria analysis tool coupled with GIS to improve the robustness of the potential of desealing map (with regard to the benefit/risk analysis, to the uses, to the points of view of the stakeholders, and to uncertainties) and help building desealing scenarios, and ii) a serious game dedicated to the stakeholders to facilitate the understanding of the city complexity, the issues of desealing and the co-construction process. Taking into account local specificities (mainland and overseas) will ensure the replicability of the work in different territories. Legal discrepancies will also be addressed. The project will also produce thematic maps on the pilot study area (Nantes Métropole territory) that improve knowledge of the urban system. To help building scenarios, the benefits of desealing watersheds on water runoff and of desealing in urban heat islands on thermal comfort will be assessed by numerical modelling. Artificial intelligence and geostatistics are used to address uncertainties, which will be qualified in a concerted way to facilitate their combination under GIS and their consideration in the decision-process.