The proliferation of artificial obstacles in rivers (dams, dams, walls of all kinds and other human constructions) is an ecological problem that alters the natural functioning of these river channels.. According to a recent study, in Spain there would be about 5,700 obstacles of this type, distributed throughout the territory. They are barriers in the rivers that cause the migration of native species and the arrival of exotic ones, in addition to deteriorating the dragging of sediments towards the coast. However, Spain is leading the efforts to remove these obstacles, according to a European study.
Specifically, the Dam Removal Progress 2021 report, which is prepared every year by a series of European conservation entities, reveals that Spain was, by far, the State where the most river obstacles were removed in that year.
A total of 108 works, infrastructure and other constructions that alter rivers were demolished or removed in 2021. This is obviously a modest figure compared to the total number of items to be removed, but it is well above second-ranked country Sweden, with 40 obstacles removed from its rivers. They are followed by France (39), Finland (16) and the United Kingdom (10).
The main elements that disturb the natural fluidity of rivers (and, with it, their natural mechanics and their biodiversity) are dams, dams, weirs (walls to redirect water to crops) and also constructions of all kinds, including homes or warehouses, often abandoned.
Some of the examples of river restoration in Spain included in the report are the demolition in 2021 of the dams on the Pámanes river (Cantabria) and the Oria river (Guipúzcoa), as well as the demolition of the Matabosc weir, on the Ter river.
In total, 239 barriers, dams and dams were removed in 17 European countries last year. According to the report, this is the highest figure withdrawn in Europe since these organizations accounted for these restoration works.
“The removal of barriers to restore the longitudinal connectivity of rivers is currently a trend in Europe,” the authors of the report point out. “The accelerated rate of removal of these fluvial barriers is justified by the imultiple impact that such barriers cause on natural ecosystemsincluding altered sediment loads and flow regimes and temperatures, nutrient modification, habitat degradation, transformation of aquatic communities, and reduction in species abundance,” he adds.
When a dam, reservoir or any other type of river barrier is installed, the flow of the river is disturbedcausing the migration of local fish species, favoring the prevalence of exotic ones and reducing the dragging of sedimentary material towards the coast, recalls WWF, which on several occasions has asked the administrations for more agility in these actions.
“Over the years, those structures that once had a function of collecting water, preventing overflows, transfers… end up becoming obsolete and, far from retiring, they are abandoned to their fate, seriously damaging rivers and generating also a negative landscape and visual impact on the natural environment”, they add.
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