Periodic Reporting for period 1 - CONCRETER (Groundwater flow CONtrols on CRitical zonE ThErmal Regime)
Reporting period: 2023-06-01 to 2025-11-30
Modern hydrogeology has been built on the idea that the temperature distribution in the upper kilometer of continental landmasses is in quasi-equilibrium and is determined by the long-term ground surface temperature and the heat flux from the Earth’s interior. The presumed thermal stability of groundwater is important for many groundwater and stream ecosystems which cannot tolerate a wide temperature range and face growing threats from climate and land-use changes. Yet, recent results have evidenced the great impact of ongoing atmospheric warming on shallow groundwater temperatures. Groundwater flow is expected to strongly affect groundwater and stream warming trends. A major issue is that existing modeling frameworks have largely sidestepped (1) the complexities associated with multi-scale heterogeneity in groundwater flow, and/or (2) the transient nature of groundwater fluxes and surface temperature. Furthermore, direct field evidences of the impact of climate and anthropogenic forcings on the temperature distribution are rare. The CONCRETER assesses the role of groundwater dynamics in shaping the thermal regime of the critical zone, the shallow subsurface where the water, element, energy and biological cycles interact.
The focus on the interaction of subsurface heterogeneity with heat transport processes requires:
(WP1) The development of original numerical models to explore large-scale thermal behavior in a fractured geological formation.
(WP2) The development of novel experimental methodologies to perform dynamical pore scale optical measurements of temperature.
(WP3) New critical in situ data to directly estimate the distribution of groundwater fluxes and rock thermal and to constrain the models developed within WP1.
(WP4) The further development of advanced numerical models to separate the effects of fluid flow and of surface warming.
(WP5) To measure changes in temperature on well-characterized sites chosen to isolate each effect (natural flow, pumping, surface heating). Complemented by data on the heterogeneity of hydraulic and thermal properties (WP3), we will analyze collected data sets using the newly developed 3D numerical models of flow and heat transport (WP1 and WP4).
Through these steps, CONCRETER will lay new theoretical and practical foundations to understand the interplays between flow and heat transport processes, fully integrating the up-to-now neglected role of the groundwater hydrodynamics and the specific role of flow variability.
The focus on the interaction of subsurface heterogeneity with heat transport processes requires:
(WP1) The development of original numerical models to explore large-scale thermal behavior in a fractured geological formation.
(WP2) The development of novel experimental methodologies to perform dynamical pore scale optical measurements of temperature.
(WP3) New critical in situ data to directly estimate the distribution of groundwater fluxes and rock thermal and to constrain the models developed within WP1.
(WP4) The further development of advanced numerical models to separate the effects of fluid flow and of surface warming.
(WP5) To measure changes in temperature on well-characterized sites chosen to isolate each effect (natural flow, pumping, surface heating). Complemented by data on the heterogeneity of hydraulic and thermal properties (WP3), we will analyze collected data sets using the newly developed 3D numerical models of flow and heat transport (WP1 and WP4).
Through these steps, CONCRETER will lay new theoretical and practical foundations to understand the interplays between flow and heat transport processes, fully integrating the up-to-now neglected role of the groundwater hydrodynamics and the specific role of flow variability.
WP 1. Within WP1 we develop a new generation of heat transport model to explore thermal behavior in fractured media. We have updated the DFN.lab software (https://fractorylab.org/dfnlab-software/(opens in new window)) to unlock the exploration of advective–diffusive heat transport in heterogeneous 3D fracture networks. The model development was performed by researchers from the Fractory (a joint laboratory established in between the CNRS, the Univ. of Rennes and the company ITASCA). We have developed a nonconforming discretization method, enabling an independent mesh generation for fractures elements and matrix. This approach allows to significantly reduce the calculation time. We are currently validating this numerical scheme: several simple test cases have been developed based on comparisons with analytical solutions or on simulations using other numerical tools.
In parallel, we have studied heat transport behavior at fracture intersections. The numerical simulations are conducted with OpenFoam, solving the mass, momentum, and energy conservation equations in the fractures coupled to heat conduction in the impermeable rock matrix. The results characterize the effect of the fracture aperture, the angle under which the fractures intersect, and the thermal conductivity of the matrix on the heat transport at fracture intersections for different Péclet number.
WP 2. A major technological challenge addressed in this project is the design and development of new experimental methodologies to perform dynamical pore scale optical measurements of temperature. We have proposed a novel application of optical thermometry aiming to evaluate local thermal nonequilibrium effects on heat transport in heterogenous porous media. This experimental approach overcomes technical challenges of current experimental techniques.
WP 5. I was analyzing new temperature data illustrating the complex interplay of climate warming and anthropogenically enhanced groundwater flow on subsurface thermal regimes from two sites in different hydrogeological settings. While providing for the first time a physical understanding of the heat transport phenomena in exploited aquifers, our heuristic modeling approach used in this work limits its ability to capture site-specific characteristics. To consider these factors and to predict thermal subsurface regime more in details, we develop now more sophisticated models of the chosen field sites based on the discrete fracture network approach from WP1.
In parallel, we have studied heat transport behavior at fracture intersections. The numerical simulations are conducted with OpenFoam, solving the mass, momentum, and energy conservation equations in the fractures coupled to heat conduction in the impermeable rock matrix. The results characterize the effect of the fracture aperture, the angle under which the fractures intersect, and the thermal conductivity of the matrix on the heat transport at fracture intersections for different Péclet number.
WP 2. A major technological challenge addressed in this project is the design and development of new experimental methodologies to perform dynamical pore scale optical measurements of temperature. We have proposed a novel application of optical thermometry aiming to evaluate local thermal nonequilibrium effects on heat transport in heterogenous porous media. This experimental approach overcomes technical challenges of current experimental techniques.
WP 5. I was analyzing new temperature data illustrating the complex interplay of climate warming and anthropogenically enhanced groundwater flow on subsurface thermal regimes from two sites in different hydrogeological settings. While providing for the first time a physical understanding of the heat transport phenomena in exploited aquifers, our heuristic modeling approach used in this work limits its ability to capture site-specific characteristics. To consider these factors and to predict thermal subsurface regime more in details, we develop now more sophisticated models of the chosen field sites based on the discrete fracture network approach from WP1.
-We have developed a new generation of heat transport model to explore large-scale thermal behavior in a fractured geological formation.
-We have proposed a unique laboratory experimental approach compared to other existing setup. It provides an entirely new vision of the intimated interaction of flow and heat transport processes at pore scale.
-We have demonstrated that often neglected groundwater hydrodynamic (natural and/or forced) has a major impact on critical zone thermal regime.
-We have proposed a unique laboratory experimental approach compared to other existing setup. It provides an entirely new vision of the intimated interaction of flow and heat transport processes at pore scale.
-We have demonstrated that often neglected groundwater hydrodynamic (natural and/or forced) has a major impact on critical zone thermal regime.