The submarines springs of Port Miou and Bestouan form a continuous flow of water from the continent that discharges into the sea. This underground water flows in karstic conduits of metric to decametric dimensions that were formed in the subsoil of the calanques from Marseille to Cassis, in lower limestone Provence. This hydrosystem of Port-Miou, represented by the emblematic spring of Port-Miou, goes far beyond the coastal zone and extends over a large part of the geological units of Beausset-Calanques and Sainte Baume (catchment area >400km²), up to more than 1000 meters of altitude. At the outlet, the groundwater has a variable salinity over time depending on the flow, acquired at great depth below sea level, at more than 235 meters deep, several kilometers inland. Upstream, it is a strategic water resource for the region, close to the areas of need of the metropolises, and sheltered from the natural hills of the Sainte-Baume Natural Regional Park and the Calanques National Park.
This hydrosystem is also a real open-air laboratory for the study of the water cycle in the Mediterranean region, in the immediate vicinity of the University of Aix-Marseille. The coastal karst springs are particular objects of study, characterized by a brackish water with variable salinity acting as a natural marker which allows to study the hydrodynamic functioning of the karst and the mechanism of saline intrusion. The long-term evolution of groundwater flow and salinity is directly related to global changes (climate, eustatic variations). Coastal springs are the result of flow and transport processes on the mainland, in the spring’s recharge watershed, and interactions with the sea, which enters the land at depth and receives this fresh or brackish water input in the nearshore zone. The Port-Miou hydrosystem thus contributes to the following objectives:
- monitoring of a network of saline intrusion in the regional aquifer and local eustatic variations ;
- study of the saline intrusion mechanism in heterogeneous coastal aquifers and consequences on water resources ;
- quantitative and qualitative assessment of groundwater inputs to the sea: flows, biodiversity ;
- methodological development for the hydrodynamic study of heterogeneous aquifers, modeling and geochemistry ;
- study of karstification in carbonate reservoirs and its impact on groundwater flow dynamics and storage ;
- study of the relationship between rainfall, land use and floods.
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