“An enigma” some say. The Accès barrage sur la rivière souterraine de Port-Miou is an enigma. Today we explore this fantastic freshwater reservoir. But its secrets are not easily given up.
The Calanque de Port Miou serves as a coastal gateway. It leads to the Massif des Calanques. This extends all the way to Marseille. Its beauty comes from its unique geology.
This calanque formed from lower Cretaceous limestone. Abandoned quarries reveal a quasi-3D view of the rocks. You can see the fracturing and karstification processes.
The Accès barrage sur la rivière souterraine de Port-Miou. It is located 500 meters from the sea. It was built in the 1970s. The barrage helps monitor the brackish water’s changes. Water passes through the barrage’s four nozzles. During floods, it can overflow the underground threshold.
Beneath our feet lies a mystery. The underground river of Port-Miou. Divers first ventured into it in 1953. In 2016, explorers reached over two kilometers. They went as deep as -233 meters. This confirms the cavity’s importance. It seems to be the mouth of one of Europe’s longest underground rivers.
In 1976, a subterranean dam was constructed. It was placed 150 meters from the opening. The goal was to stop seawater from entering the river. Sadly, the water upstream remained brackish. So it was undrinkable. The barrage now is a starting point for science.
The Port-Miou site studies peri-Mediterranean karsts. It overlaps other watersheds. The Sainte-Baume mountain range collects rainwater. The Port-Miou spring became an experimental lab in the 1970s. An artificial tunnel grants access to the underwater gallery. It is drowned 500 meters inland.
Romans used this river’s water. In times of flood, it can reach 150 cubic meters per second. It winds through limestone rocks. It plunges to 230 meters deep.
The dam was meant to block the sea’s salt. But even two kilometers inland, salt traces exist. The river’s average flow is seven cubic meters per second. It could supply water to a city like Marseille.
The submarine springs of Port Miou and Bestouan create a flow. It goes from the land into the sea. This water moves through karstic conduits. These formed beneath the calanques from Marseille to Cassis.
Researchers study geology and more here. They seek to understand the river’s origins. In 2020, a new species was found here.
The cool water in Cassis is due to these springs. After heavy rains, you can see the turbulence.
The freshwater mixes with intruding seawater. This creates brackish conditions. The water quality affects the whole Calanque.
The Accès barrage sur la rivière souterraine de Port-Miou. It stands as a testament to nature’s hidden wonders. Its study continues to reveal secrets. Each discovery enriches our understanding.