On average, there is about one barrier per 1.4 kilometres of stream, in Germany even two barriers per kilometre. Small transverse structures with an impoundment height of less than two metres account for the lion's share. The study also shows opportunities for reconnecting streams and rivers.
The study, led by researchers at Swansea University's Centre for Sustainable Aquatic Research (CSAR) in the UK, reveals that Europe's rivers as a whole include at least 1.2 million transverse structures within their course, including large dams, but mainly a large number of low-head structures such as weirs, culverts, fords, sluices and ramps. Using barrier modelling and extensive field ground-truthing, the research team showed that, on average, one barrier per 1.4 kilometres of river restricts the movement of the river and its creatures; in Germany, the figure is as high as two barriers per kilometre in rivers and large streams. 85 percent of the transverse structures have less than two metres of impoundment height.
First pan-European assessment of river fragmentation
The study took place within the framework of the EU research project "Adaptive Management of Barriers in European Rivers (AMBER)". The researchers mapped river-fragmenting transverse structures across Europe and produced the first comprehensive barrier inventory, the AMBER Barrier Atlas. "The extent of river fragmentation in Europe is much higher than anyone had anticipated," said Barbara Belletti, a river geomorphologist who led the study at Italy's Politecnico di Milano and is now at CNRS, the French national centre for scientific research.
IGB PhD student Helena Hudek, together with other IGB colleagues, has checked the official statistics on transverse structures by field mapping (‘ground-truthing ‘) in 15 European countries. She described her impressions from the field: "We were shocked to see that, for example, many streams in south-eastern Europe were dry because the water had been diverted through pressure tunnels to a hydroelectric power station. In other streams we found almost no fish and small animals because they were regularly washed away by water surges from a hydroelectric power plant."
Solutions to restore connectivity
"Many barriers are no longer needed, and removing them offers unprecedented opportunities to improve stream continuity," says Prof Carlos de Garcia de Leaniz, AMBER's coordinator from Swansea University in the UK. As part of the project, unused weirs were removed in Great Britain, Spain, Ireland and Denmark - in Denmark, 310 river kilometres have already been reconnected.
Study co-author PD Dr. Martin Pusch from the IGB is an expert in river basin management: "The AMBER Barrier Atlas gives us the opportunity to reverse the fragmentation of rivers all over Europe; to rehabilitate many of these barriers through simple technical measures, or to remove them completely through renaturation measures. Locks and large hydropower plants should be equipped with functioning fish passes for both directions of migration, and small hydropower plants, which hardly contribute to the energy transition, should be dismantled. In this way, the eel population in Germany could be protected, and salmon and sturgeon could also permanently colonize our streams and rivers. At the same time, these freshwaters would be made fit for climate change and greatly enhanced as recreational areas."
Results feed into the Biodiversity Strategy 2030
The results of AMBER have already reached political decision-makers. "Our results feed directly into the new EU Biodiversity Strategy and will help to reconnect at least 25,000 km of Europe’s rivers by 2030", said Carlos de Garcia de Leaniz.
Citizens create knowledge: The Barrier Tracker
With a free app, the Barrier Tracker, anyone can document barriers in water bodies. The georeferenced data and photos are used to create a map of Europe of transverse structures. It helps to set priorities for the adaptation and removal of barriers.
