A transmitter and a set of receivers measure the resistivity of the subsea layers to locate fresh water.
© Micallef et al., 2021. Review of geophysics
Against a backdrop of mounting demands linked to climate change, rising sea levels and water abstraction, the AQUIMER project aims to characterise the transition between freshwater and saltwater aquifers in the Roussillon plain. This transitional phenomenon occurs in coastal areas where freshwater aquifers may come into contact with saltwater. The transition is complex and sometimes occurs quite far from the coastline, either inland (the ‘salt wedge’ phenomenon) or beneath the sea. The aim of the planned geophysical campaign is therefore to determine the location of this transition zone between fresh and salt water at depth, to understand how it works and to predict any future changes. The freshwater reserves found in the Pliocene–Quaternary aquifers of the Roussillon plain play a vital role for this region, both for crop irrigation and for the supply of drinking water.
The AQUIMER project, funded by the French Research Agency (ANR), brings together multidisciplinary scientific teams coordinated by BRGM. At sea, MAPPEM Geophysics, supported by the GEOCEAN (University of Brest) and CEFREM (University of Perpignan) laboratories, will carry out the geophysical surveys. CEFREM will also be involved in the geological modelling of the marine domain. On land, Géosciences Montpellier (University of Montpellier) will construct a geological model of the subsurface based on the data collected. Finally, IFPEN (IFP Énergies nouvelles) will use simulation to reconstruct the geological history of the region since the Miocene, some 10 million years ago, in order to understand how the strata containing the groundwater reservoirs currently being exploited were formed. BRGM will coordinate the project, take part in terrestrial geophysical surveys and develop a hydrodynamic model incorporating all of the data to simulate the future evolution of the risk of saline intrusion.
From mid-September, researchers will be mapping the subsurface without the need for boreholes, because the project will use geophysical techniques, both on land and at sea, at various scales, to monitor variations in the salinity of the aquifer water up to 15 km offshore. Sensors and cables will be temporarily installed at various points to measure the natural electrical properties of the subsurface and its response to weak electromagnetic signals. On land, a series of measurements will be carried out jointly by the municipalities of Saint-Cyprien and Canet-en-Roussillon: 25 measurement points and 15 current injection points will be distributed along a 3 km stretch, with a system designed to minimise disruption to the site and its users.
The aim of combining terrestrial and marine geophysical techniques is to locate fresh and salt water at depth, as the two do not conduct electricity in the same way. By combining measurements taken on land and at sea, researchers will obtain a continuous image of the subsurface, from the coastline out to the open sea.
The AQUIMER research project is funded by the ANR. It was launched in March 2025 and is to last 48 months
Recent discoveries have revealed the presence of large quantities of freshwater trapped beneath the sea, in the sedimentary layers that extend the coastal aquifers beyond the shoreline.
The project focuses on the Pliocene–Quaternary aquifer of the Roussillon plain (Pyrénées-Orientales département, in southern France). This aquifer, which is well documented on land, extends under the sea for several tens of kilometres, making it a particularly suitable study site for this project.
Offshore freshwater reserves represent a major opportunity that is likely to bring about changes in the management of water resources in coastal areas.
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