Location map

Key findings

• Flow reversal at a submarine karst spring: long-term monitoring provided the first complete observation of an inversac, showing that the Vise can switch abruptly from freshwater discharge to saltwater inflow into the karst aquifer.
• Hydraulic control of the inversac: the reversal is controlled by the hydraulic gradient between the karst aquifer and Thau Lagoon, taking into account the density difference between freshwater and saline water. 
• Tipping points and hysteresis: the system has two distinct thresholds: one for the onset of saltwater intrusion and a substantially higher one for recovery. Saltwater filling of the vertical karst conduit creates strong hysteresis, explaining why inversacs can persist for months. 
• Modelling and monitoring for water-resource management: combining continuous underwater monitoring, hydrogeological observations and modelling has provided a mechanistic understanding of the inversac and the basis for anticipating and mitigating saltwater intrusion into the Thau karst aquifer.

Hydrogeological model

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