For his master’s thesis, a student in hydraulic engineering EPFL imagine a dam in the Strait of Gibraltar to contain the rising waters in the Mediterranean. A work of art that would leave passing boats and aquatic wildlife while maintaining a constant level of the sea.
How will redrawn coastal areas be in 2100? Erased, eroded permanently deleted? The most optimistic forecasts envisage water will rise up to a foot, the most pessimistic talk of more than one this.
Venice and the Nile Delta could be wiped off the map. Moroccan coastal areas disappear, too. Risk of erosion, saltwater intrusion in crops or groundwater, undersized and unable to withstand the hydraulic dams variations, scenarios should not be neglected.
Ha Phong Nguyen discussed the project of a dam at Gibraltar. “The goal would be to close the Mediterranean with two dams, one between Spain and Morocco and the other between Djibouti and Yemen, to control the water level.” The simplest solution would be to close the Strait where the distance is closer. But there are only 14 km, the depth, it is 800 meters. “For this to be realistic, I had to locate the dam right of Tangier, in the Mediterranean. There are 27 km between the two continents, but it is half deep.”
The young engineer has tested numerous configurations before finding a geometry that contains water while letting the 300 daily ships, Russian submarines are positioned in this area without interrupting the crossover of animal species that migrate in the sea in winter and go into the ocean in the spring.
“Closing the Strait of Gibraltar to 90% and leaving an opening a mile, you come to maintain a constant level of the Mediterranean, on the assumption that increasing the level of the Atlantic would be at 50 cm”
His master project was to build a numerical model to simulate the currents in this passage. To validate the model it was necessary to compare the data with historical values taken during campaigns in years 70 and 90. The topographic data required are held by the Spanish Navy and are considered confidential documents. Special requests were required to gain access.
The operation of the dam
By closing the strait, the water flow speed is faster and can be used to generate energy. Currents in the strait flow in both directions. The Atlantic water flowing into the Mediterranean to compensate for evaporation from the sea is colder and less salty and therefore less dense, and will remain on the surface. There is also a movement from the Mediterranean to the Atlantic. We must add to this the phenomenon of tides. “In my model I have taken into account the tides due to the moon and the sun. In Gibraltar there are two high tides and two low tides each day. ”
But the tidal coefficients are low, the dam must rely on other energy inputs to produce the equivalent of a nuclear power plant. “With the tides, I arrived at values between 600 and 1300-H GW (gigawatt hour) says Ha Phong Nguyen. Mühleberg produces 2-3000 per year. It is essential to combine it with other systems that can produce energy such as wind turbines and geothermal wells. ”
The project will see Ha Phong probably never on the same day if it is in a shared dream with, notably, a Swiss engineer named Giovanni Lombardi, who had envisioned a rail tunnel connecting the two continents and which does could result. The movement of African and European plates remains one of the biggest obstacle to such constructions.