BRGM: the AQUIMER geophysical survey maps fresh groundwater beneath the seabed off the Roussillon coast — electrical resistivity measurements up to 15 km offshore
Since 17 September 2026, teams coordinated by the French geological survey BRGM have been running a geophysical survey on the Roussillon coast as part of the AQUIMER project funded by the French research agency ANR. The aim is to locate the transition zone between fresh and salt water deep in the aquifer — under land and under the sea — and to anticipate how it will change.
- The work concerns the Plio-Quaternary aquifer of the Roussillon plain, well known on land and extending several tens of kilometres under the sea; its freshwater reserves are used for crop irrigation and drinking water supply. The transition zone sometimes lies inland (saline wedge) and sometimes under the sea; pressure is rising due to climate change, sea-level rise and abstraction.
- Because fresh and salt water conduct electricity differently, the scientists map the subsurface without drilling: temporarily deployed sensors and cables measure the natural electrical properties of the subsurface and its response to weak electromagnetic signals, on land and at sea. On land, between Saint-Cyprien and Canet-en-Roussillon, 25 measurement points and 15 current injection points are planned along a 3 km profile; combining land and marine measurements is to give a continuous image of the subsurface from the coast out to sea.
- Marine measurements are carried out by a geophysics company supported by the GEOCEAN (University of Brest) and CEFREM (University of Perpignan) laboratories; Géosciences Montpellier will build a geological model of the onshore subsurface, IFPEN will reconstruct by simulation the geological history of the region since the Miocene (about 10 million years ago), and BRGM, besides coordinating and onshore measurements, will build a hydrodynamic model to simulate the future risk of saline intrusion.
- According to the ANR description (ANR-24-CE01-1184) the project runs for 48 months from March 2025 with ANR funding of EUR 904,368. AQUIMER is to establish a new workflow using electrical resistivity as a proxy for the distribution of groundwater bodies — calibrated at existing onshore borehole observatories — and to test the hypothesis of freshwater trapped offshore; the workflow is intended to be applicable to other shallow coastal aquifers around the Mediterranean and elsewhere.