Although invisible, groundwater plays an essential role for society as a source of drinking water or for ecosystems by providing a base flow to rivers, but it also faces significant contaminant challenges. Characterizing groundwater reservoirs with their spatial heterogeneity and temporal evolution is therefore crucial for their sustainable management.
For 4 years, the European network ITN ENIGMA (2017-2021) trained 15 PhD students on new techniques for monitoring and imaging hydrogeological systems, allowing a dynamic and spatially resolved vision of underground environments. This project coordinated by the CNRS-INSU (see box) was based on the highly instrumented sites of the SNO H+ (OZCAR infrastructure) and the main hydrogeological observatories in Europe.
In this article, a research team identifies the hydrogeological processes for which an approach combining monitoring of spatial and temporal variability, including 4D imaging, is needed: (1) groundwater flows that control (2) the transport, mixing and reaction processes of the solutes, (3) the dynamics of the non-saturated zone and (4) the interaction between surface and groundwater at the interface between different compartments of the critical zone. The study highlights recent innovations in this area and recommends a more systematic characterization of the dynamic nature of subsurface processes. This includes harmonizing open databases to store hydrogeological datasets in their four-dimensional components, in order to address emerging scientific questions and key societal issues.
Hermans, T., Goderniaux, P., Jougnot, D., Fleckenstein, J., Brunner, P., Nguyen, F., Linde, N., Huisman, J. A., Bour, O., Lopez Alvis, J., Hoffmann, R., Palacios, A., Cooke, A.-K., Pardo-Álvarez, Á., Blazevic, L., Pouladi, B., Haruzi, P., Kenshilikova, M., Davy, P., and Le Borgne, T. (2022) Advancing measurements and representations of subsurface heterogeneity and dynamic processes: towards 4D hydrogeology, Hydrol. Earth Syst. Sci. doi :10.5194/hess-2022-95