the incredible idea of ​​​​a dam on the Strait of Gibraltar resurfaces

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The idea of ​​building a dam linking Europe to Africa via the Strait of Gibraltar is far from new. It was born in 1928 from the dreams of peace of a German engineer whose Atlantropa mega-project had not seduced Adolf Hitler at the time. Since then, for rather economic reasons, kings, engineers and scientists regularly toy with the idea of ​​taking up the challenge.

This time, it is the fight against global warming that resuscitates the project. The Intergovernmental Panel on Climate Change (IPCC) has once again warned in its latest report: if our greenhouse gas emissions continue at this rate, damage caused by coastal flooding will be “multiplied by 10 at the end of the 21st century”. The rise in water will reach between 61 and 101 cm by 2100, threatening the coasts and its populations. To protect the Mediterranean coasts, the idea of ​​the dam was therefore revived again.

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In 1928, a German engineer Herman Sörgel imagined a peaceful world through the existence of three balanced continents: America, Asia and Atlantropa. The latter would arise from a meeting of Europe and Africa under the common authority of the Europeans. The idea is to close the Mediterranean via a 35 km long 300 meter high hydroelectric dam across the Strait of Gibraltar, this strategic waterway between the south of the Iberian Peninsula and the northwestern tip of Africa. . A second dam closes the Dardanelles Strait. By drying up the Mediterranean, Sörgel hopes to free up an area of ​​usable land greater than the area of ​​France (over 600,000 km2) by causing the waters to drop by 100 to 200 metres. Via another dam on the Congo River, it irrigates the Sahel, creating two inland seas in Africa, Lake Chad and a “Congo Lake”.

A visionary, Herman Sörgel has already anticipated the shortages of coal and oil to come in an increasingly fossil fuel-intensive world. Its system of dams, supplemented by a hydroelectric plant between Sicily and Tunisia, is also designed to develop an alternative source of energy, that of the surface currents circulating between the Atlantic Ocean and the Mediterranean, whose volume of water equals 12 Niagara Falls per second. A colossal hydraulic force which would have made it possible to operate hydroelectric turbines capable of producing the equivalent of 31 current nuclear reactors.

Atlantropa: a qualified vision of “mad and utopian” by the marine biologist Alexandre Meinesz who, more than 90 years later, nevertheless defends it in a book, Protect marine biodiversity (Odile Jacob), published in 2021. For him, the climate emergency and the rising waters are updating Sörgel’s old project. Closing the Mediterranean with a dam at Gibraltar would compensate for thesea ​​level rise predicted in the IPCC scenarios for the year 2100. CThe dam is also, according to Alexandre Meinesz, the only option to prevent the entire Mediterranean coastline from being artificialized by man and considerable damage being done to marine life. His vision of the dam would lead to a drop in the current level of the Mediterranean by 20 cm which, according to him, would make it possible to regain the level at the beginning of the 20th century.

Alexandre Meinesz has not quantified his project which also plans to build locks at the level of the Suez Canal to compensate for the rising waters of the Red Sea. But he estimates that 23 Mediterranean states could finance it and that rail and road communications could be set up above the dam. He insists on the fact that it will be cheaper to finance a global solution than individual dykes, especially since the current systems such as the perpendicular groynes (some 280 erected in front of the shores of Camargue and Languedoc) or the 30 km of dykes installed in front of the French coasts, will be powerless in the face of the inexorable rise in water. “QWhen we compare what the rise in water level of one meter will cost and the construction of the dam, we are in a ratio of simple to triple”assures the biologist.

But the project is complex, admits Alexandre Meinesz: it will be necessary in particular to take care not to modify the salinity and the currents, to leave enough openings to allow a communication of the biodiversity between the Mediterranean and the Atlantic and to let pass sufficient volume of water. water to compensate for natural evaporation.

In 2014, a young engineer from the Federal Polytechnic School of Lausanne, Ha-Phong Nguyen, also studied the question for his master’s degree in civil engineering. But unlike Sörgel’s project, which intended to build three dams to close off the Mediterranean (the first between Spain and Morocco, the second between Sicily and Tunisia and a third in the Dardanelles strait), Ha-Phong Nguyen is considering two: one between Spain and Morocco, the other between Djibouti and Yemen, to regulate the level of the Red Sea via the Suez Canal. And, on the Gibraltar side, he would avoid the narrowest zone (14 km) but the deepest (800 meters) and build his dam east of Tangier: “There are 27 kilometers between the two continents, but it’s half as deep”he explained.

The Strait of Gibraltar. (GOOGLE MAPS)

To limit the impact on maritime traffic and the circulation of cash, the young engineer had planned to close the strait only at 90%, leaving an opening of one kilometer which, according to him, would make it possible to “keep constant the level of the Mediterranean, assuming that the increase in the level of the Atlantic would be 50 cm”. Ha-Phong Nguyen also made the calculation of the energy production that could be obtained from the dam, much less optimistic than that of Sörgel. “With the tides, I arrived at values ​​between 600 and 1300 GWh”, he explained. He compared at the time with the Swiss nuclear power plant of Mühleberg which produced, before its shutdown, 2 to 3000 GWh per year. “It is essential to combine it with other systems that can produce energy such as wind turbines and geothermal boreholes”, he added. However, there remains a major obstacle making these projects probably unrealizable: le displacement of the African and European plates.

In 2016, it was Jim Gower, of the Institute of Ocean Sciences of Canada, who also presented a dam project in the journal Natural Hazards [article payant]. Like Ha-Phong Nguyen, his first idea was to build it in the shallower zone, 25 km long at 284 meters deep. He planned to use the local rocks that boats would drop on the area, creating their progressive stacking. Cost of the future structure: some 45 billion euros, financed by the production of energy which would increase as the general level of the oceans would rise. He also considered tourism as a source of funding.

Another dam project, this time 100% European, is envisaged by Dutch scientists, on the same principle: to contain the water. But this time, it is the North Sea and the Baltic which are concerned. 475 km long between northern Scotland and western Norway and 160 km between the western tip of France and south-west England, the Northern European Enclosure Dam would protect the coasts of 15 European countries. The costs of such a project have been estimated between 250 and 500 billion euros, i.e. only “0.1% of the gross national product, annually over 20 years, of all the countries that would be protected by such a dam”, according to Dr Sjoerd Groeskamp, ​​an oceanographer at the Royal Netherlands Institute for Maritime Research, who did the calculations with his Swedish colleague Joakim Kjellson of GEOMAR in Kiel, Germany. They published their study in February 2020 in the scientific journal Bulletin of the American Meterological Society.

According to them, the construction of such a dam is “technically feasible”the maximum depth of the North Sea between France and England being barely a hundred meters and an average of 127 meters between Scotland and Norway. “We are currently able to build fixed platforms at depths greater than 500 meters”emphasizes Sjoerd Groeskamp.

But the authors recognize that the consequences of this dam for the fauna of the North Sea would be considerable. “The tide would disappear in a large part of the North Sea, and with it the transport of silt and nutrients. Eventually the sea would even become a freshwater lake. This will drastically change the ecosystem and therefore also have a impact on the fishing industry, explains the oceanographer. In the final calculation, we must also take into account factors such as the loss of income from fishing in the North Sea, the increased costs of navigation across the North Sea and the cost of gigantic pumps to transport all the water from the river that currently flows into the North Sea on the other side of the dam. […] This extreme barrage is more of a warning than a solution. If we do nothing, then this extreme barrage may well be the only solution.”concludes Groeskamp.


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