España tiene inventariadas más de 19.000 barreras transversales en los ríos de demarcaciones intercomunitarias, pero se estima que en realidad hay muchas más, decenas de miles de obstáculos -generalmente en desuso- que no figuran en inventarios ni registros oficiales. La mayor parte de ellas son saltos verticales de escasa altura, construidos para permitir la derivación o sobreelevación de aguas superficiales para distintos aprovechamientos humanos. La fragmentación y alteración de nuestros cauces por estas barreras artificiales y las presiones asociadas es una de las principales causas estructurales del deterioro de nuestros ríos.
En 2020, un estudio estimó en torno a 1,2 millones de barreras en los cauces de 36 países europeos, 15% de ellas estarían obsoletas (Belletti, B., Garcia de Leaniz, C., Jones, J. et al., Nature 588, 436–441 (2020). Este último estudio se llevó a cabo como parte del proyecto Horizon 2000 “Adaptive Management of Barriers in European Rivers” (proyecto AMBER), financiado con fondos de la UE.
Cuando estas barreras dejan de ser funcionales, su eliminación contribuye positivamente a la mejora estética de los paisajes fluviales y genera sustanciales beneficios para otras actividades económicas, como la recreativa. La demolición de barreras obsoletas - o la permeabilización cuando aún se encuentran en uso - es una de las actuaciones más comunes en los proyectos de restauración fluvial. Con ello se reconectan los caudales líquidos y sólidos y desfragmenta la continuidad fluvial. Uno de los principales objetivos de los proyectos de eliminación/permeabilización de barreras es hacer posible que los peces migratorios puedan volver a recolonizar aquellos ríos que una vez quedaron fragmentados.
La Unión Europea es muy sensible a este tema, tanto es así que en su Estrategia Europea para la Biodiversidad para 2030 se fijó la restauración de 25.000 km de ríos en Europa. Para evaluar la evolución del cumplimiento de este objetivo y el progreso y el impacto de la demolición de barreras, Dam Removal Europe (DRE)* publica informes de progreso anual.
Según el informe “Dam Removal Progress 2021”, durante el año 2021, al menos 239 barreras transversales al eje longitudinal de los ríos fueron eliminadas en 17 países europeos. De ellos, España destacó en primera posición con 108 casos (un 45% del total europeo). De esas barreras demolidas, el 87% se correspondió con azudes.
* Dam Removal Europe (DRE) es una coalición de 7 organizaciones: the World Wildlife Fund, The Rivers Trust, The Nature Conservancy, the European Rivers Network, Rewilding Europe, Wetlands International, y the World Fish Migration Foundation.
Nº de barreras demolidas por país en 2021 (En verde, los países que durante 2021 han demolido su primera barrera).
Mapa de los países europeos que durante 2021 demolieron barreras (El gradiente de color refleja el número de casos de demolición).
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