More than a million barriers cut off the rivers of Europe | Science



“What defines a river is that it flows, if it does not, it is not a river”, says Carlos García de Leániz. This professor from the University of Swansea (United Kingdom) has coordinated, together with his colleague from the Politenic of Milan, Barbara Belletti, a huge study that has found more than 1.2 million barriers that cut off the passage to the rivers of Europe. The work shows that the highest density of obstacles are found in the most developed areas of the continent and only escape the north of the Scandinavian region, Iceland or the Balkan area. The worst part is that many of these walls of the water have been abandoned for decades.

The work, just published in the scientific journal Nature, has needed the assistance of fifty scientists. For four years they have compiled the inventories of river barriers for 36 countries. On that basis and without believing what the books said, they traveled 2,715 kilometers of 146 rivers, finding many more. Then, extrapolating the differences between records and what they saw, they have estimated at 1,213,874 the dams, dikes, locks, weirs, waterwheels, reservoirs, gates … that cut off the rivers.

“In Spain the inventory of dams and other barriers is made by the confederation of each basin, but in Italy each province through which the river passes has its own. Only a few countries like France and Sweden have it centralized in a single authority ”, says the engineer of the Fish Migration Foundation and co-author of the study Pao Fernández. She is an expert in the dismantling of dams has led this compilation of inventories for which “it was necessary to find that authority for each of the rivers studied in the 36 countries.”

The total inventory shows that there were 629,955 obstacles, with a density of 0.38 barriers for each river kilometer. And this is the database that has fed the AMBER atlas. After those acronyms in English is the Adaptive Barrier Management in European Rivers, a project funded by the H2020 program of the European Union. It is the first atlas of these characteristics, with the typology, location, state of use … that is made in the world, but it was not enough.

“We knew there had to be many more, especially the smaller ones,” says Fernández. And he gives the examples of France and Spain. The first has registered 70,000 infrastructures deployed in its rivers, while the second has barely 20,000. “Being countries with similar size, climate, culture and history, it was impossible for Spain to be below 50,000,” he adds.

So in a second part of the project, the scientists divided the route of almost 2,800 kilometers of various sections of 146 European rivers looking for what was not registered. They had to correct upwards what the files said, since they ignored by more than half the actual figure mentioned above 1.2 million. With the updated data, the density rises to 0.74 barriers per kilometer of river. But there are huge differences by country. For example, in Montenegro they hardly encountered obstacles (0.005 per km), while in the Netherlands, land under water, there are 19.44 per km.

“In Spain the number of barriers is higher than the European average”, clarifies César Rodríguez, secretary general of AEMS-Ríos con Vida, one of the collaborating partners of the AMBER project. “Here we find a barrier every kilometer,” he specifies. Rodríguez and other volunteers traveled 20 kilometers of five rivers from as many hydrographic confederations, counting and classifying the obstacles they encountered thanks to the citizen science app Barrier Tracker.

The most abundant obstacles are weirs, small dams that draw water, generally for irrigation. Many of the obstacles did not appear in the records and he estimates that up to 20% of them were in disuse. “This field validation allowed us to calibrate the inventory data,” he completes. And that calibration is what forced more than doubling the official numbers of barriers.

Although we always think of large dams for the generation of electricity or reservoirs to satisfy us, the study shows that only 1% of the barriers exceed 15 meters, while 68% are lower than two meters. 30% of them are dams to control or divert the flow of water. Another third are ramps and the like to alter the riverbed and 17% are conduits such as the sewer system.

“Everything that humans have been doing with rivers, taking their water, preventing their flooding, obtaining electricity … is to prevent it from flowing,” says García de Leániz, the main author of this research. For him these data further aggravate the state of Europe’s rivers. “Fragmentation does not depend on the height of the obstacles, but on their number,” he adds. The European Union approved its Biodiversity Strategy for 2030 focused on the recovery of the natural last summer. The objective is to return 25,000 kilometers of river to its free flow. You could start with the at least 100,000 now-outdated barriers listed in this broken river atlas.

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