A drop does not fall in a straight line: a rationale for the width of stalagmites
How the physics of falling droplets helps shape stalagmites
Detailed borehole, hydraulic and tracer experiments revealed how fracture connectivity, the weathering interface and groundwater-level fluctuations control groundwater flow and solute transport. The research highlighted the importance of preferential horizontal flow along the weathered–fractured interface and showed that declining groundwater levels can compartmentalize the aquifer.
Climate-change-induced seismicity
How meltwater from a warming cryosphere can trigger earthquakes in the Mont Blanc Massif
Fontaine de Nimes karst system (France)
Multi-tracer investigations and modelling revealed the structure and preferential flow paths of the Fontaine de Nîmes karst system. The research demonstrated how groundwater storage can initially attenuate rainfall-runoff, but how aquifer saturation and rapid conduit flow can subsequently amplify flash-flood response. These findings led to a hydrogeological forecasting approach for karst floods.
Fractured crystalline aquifers
Hydrodynamic properties and groundwater budget
The hydrodynamic properties of the weathered-fractured layer of a hard-rock pilot watershed in a granitic terrain are characterized using hydraulic tests at different scales.
Jean-Christophe Maréchal est hydrogéologue, spécialiste du fonctionnement des eaux souterraines et des aquifères fracturés et karstiques.
La randonnée hydrogéologique: un moyen de rendre visibles les eaux souterraines
Vulgarisation scientifique
Geochemistry, hydrological modelling and wavelet analysis identify groundwater origins and mixing, characterize multi-scale karst dynamics, and quantify the effects of groundwater management on water resources and flood response.
Multi-scale understanding of a heavily exploited crystalline aquifer, showing how weathering and sub-horizontal fracturing control aquifer architecture and groundwater flow, how monsoon rainfall recharges the system, and how intensive irrigation pumping drives long-term groundwater depletion.
Mont Blanc Mountain (France & Italy)
Deep, persistent groundwater system in fractured crystalline rock, supplied by high-altitude recharge, detectable through thermal anomalies, and capable of influencing seismic activity through changes in fluid pressure
Vegetation controls water availability → the regolith stores and delays water → groundwater flows through the crystalline aquifer → groundwater exports the products of weathering.
Integrated geological, geophysical and hydrogeological investigations revealed the structure, extent and recharge areas of the karst aquifers of the Plateau de Sault. Multi-tracer approaches characterized groundwater circulation and the connections between recharge zones and major karst springs. The work quantified a substantial groundwater resource and identified areas of contrasting vulnerability, providing a basis for sustainable groundwater-resource management.
Vise karst system and Thau lagoon (France)
Long-term monitoring of the Vise submarine karst spring provided a complete observation of an inversac, revealing an abrupt switch from freshwater discharge to saltwater intrusion into the Thau karst aquifer. The reversal is controlled by the hydraulic gradient between the aquifer and the lagoon, with two distinct tipping points and strong hysteresis caused by saltwater filling the vertical karst conduit. Combining underwater monitoring and hydrogeological modelling established the mechanism of the inversac and provides a basis for anticipating and managing saltwater intrusion.
Vise & Thau: When a Spring Flows Backwards - The Inversac of the Vise Submarine Karst Spring
Submarine spring, flow reversal and saltwater intrusion
Sous nos pieds, la circulation invisible de l'eau souterraine
