C+S April 2021 Vol. 7 Issue 4 (web)

Over the course of the EU project “FIThydro”, research and industry partners studied the ecological impact of hydropower plants. ETH Zurich’s Laboratory of Hydraulics, Hydrology, and Glaciology (VAW) has developed a protection and guidance system that can help migra- tory fish to safely bypass hydropower turbines. Hydropower plants can have a major environmental impact. They dam up rivers, change aquatic habitats, and hinder migrating fish, which can be injured or killed by the turbines, trash racks, and flood relief systems. The Swiss Waters Protection Act and the EU Water Framework Direc- tive aim to mitigate these negative effects. However, many older hy- dropower plants in particular do not meet the new requirements – and have to be retrofitted. For each power plant, cost-effective measures must be individually determined considering its specific case. “It’s important to incorporate specific regional fish passage design that take into account the vital needs of local species, the hydraulic conditions at the site and the layout of each particular power plant,” explains Robert Boes, Professor of Hydraulic Engineering and head of the Laboratory of Hydraulics, Hydrology, and Glaciology (VAW) at ETH Zurich. A pan-European survey of hydropower plants VAW was involved in the four-year Horizon 2020 “FIThydro” project funded by the European Research Council. The project team, comprised of 26 European research institutions and companies, studied 17 sites in eight countries to examine the impact of hydropower plants on river ecosystems and in particular on fish. VAW contributed several labora- tory and field studies, some in collaboration with regional partners. By looking at the Schiffmühle plant on the Limmat river and the Ban- nwil plant on the Aare river, VAW and the project partners initially studied existing methods and approaches to assess the environmental impact of hydropower plants and refurbishment measures. “We wanted to identify knowledge gaps and find out how we can improve the cur- rent situation and the already implemented measures,” says Boes. Fish migrate upstream and downstream It was unclear, for instance, which upstream and downstream bypass systems are most suitable for which fish species and which conditions are ideal for fish to find them. VAW researchers and their partners measured the flow velocities and monitored fish movements by tag- ging a few thousands of fish with passive integrated transponders (PIT) around the Schiffmühle hydropower plant. The monitoring showed Towards more fish-friendly hydropower plants By Michael Keller

that many fish species in the Limmat are able to effectively use the technical and near-natural fish passage solutions to move upstream. Fish migrating downstream have to swim through the turbines of a hydropower plant if no other downstream option is available. This is where fish can injure themselves on the turbine blades, and they are also exposed to strongly fluctuating pressure. At Bannwil hydropower plant, the project partners used high-tech sensors, monitoring technol- ogy and various models to study the passage of downstream migrating fish through the turbines and over the weir. It turned out that the passage at hydropower plants can be hazardous to fish not only because of the turbines. When descending over weirs, they can also be injured by the strong currents in the stilling basin A safe guidance system for fish: a specially designed bar rack effectively guides downward migrating fish past the turbine, only slightly limiting the power plant’s operations. Illustration: VAW / ETH Zürich

The Schiffmühle hydropower plant on the Limmat river. Photo: Limmatkraftwerke AG



April 2021

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