Quantifying groundwater through gravity variations

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Gravimeter in the Vallon de Réchy (Copyright: UNINE / L. Halloran
Gravimeter in the Vallon de Réchy (Copyright: UNINE / L. Halloran

At a time when climate change is causing intense droughts to alternate with torrential rains, the RADMOGG project aims to assess the dynamics of the underground reservoirs to which the blue gold that falls from the sky flows, based on the measurement of minute variations in the Earth’s gravity. The project’s initiator, Landon Halloran, assistant professor at the University of Neuchâtel’s Centre for Hydrogeology and Geothermal Energy (CHYN), presented its objectives at the Swiss Geoscience Meeting on November 17 and 18 in Mendrisio (TI ).

It’s a little known fact, but the constant of gravity, the famous ’g’ of terrestrial acceleration in the physics courses taught in high school, is not quite a constant. Depending on the composition of the subsoil, it undergoes very minute variations, of the order of a few billionths of a unit, but which can be detected using a gravimeter. By measuring ’ g ’ as a function of time, we can deduce the variations in the height of water beneath the gravimeter, and thus assess the dynamics of groundwater as a function of time.

It is precisely this property, particularly suited to mountainous regions, that Landon Halloran and his colleagues are exploring with the aim of developing both the methodology and the understanding of aquifer resources through gravimetry. Two sites have been selected. The first is the Röthenbach, in the Bernese Emmental," explains the researcher. Easy to access, it already has a certain level of instrumentation. There, in collaboration with the Swiss Federal Institute of Metrology (METAS) Berne, we are sure to obtain a good data set to improve our methodology and test the limits of hydro-gravimetry. ’

The second site is in the Valais region. Although less accessible, the Tsalet, in the Vallon de Réchy, is a place where scientists expect to observe particularly pronounced hydrological changes, linked to climate impacts. Here," continues Landon Halloran, "we’ll be using hydro-gravimetry to determine, for example, the underground export of water from the watershed, something almost impossible to measure directly, but important for hydrological balances. This will provide invaluable information for improving numerical models to calculate, for example, the impact of shorter winters in the future.

Supported by the Swiss National Science Foundation (SNSF), the RADMOGG project began this spring and will run until the end of March 2026. Led by the CHYN under the direction of Landon Halloran, it is being carried out in partnership with the METAS Federal Institute of Metrology and the Centre de recherche sur l’environnement alpin (CREALP) in Valais.

Link: www.ljsh.ca