Fish Passage through a Hydrodynamic Double-Screw: An Alternative Solution for Restoring River Connectivity

Freshwater fish depend on a complex system of differing habitats since a variety of life-history-demands need to be fulfilled. Migrations are undertaken for spawning, food uptake, dispersion, or colonization. Dams and weirs constructed for hydroelectric power generation or river regulation can block or delay upstream fish migration and thus contribute to the decline and even the extinction of species that depend on longitudinal movements. Mortality rates resulting from fish passage through hydraulic turbines or over spillways during their downstream migration can be significant. While significant knowledge and practical experience for the planning and design of measures to ensure upstream migration of different fish species is available, effective measures for downstream migration still need further development. ‘HYDROCONNECT, a newly developed Archimedean double screw concept with low rotation frequency and therefore insignificant shear forces or pressure changes combines hydroelectric power generation and bi-directional fish passage in a single device. We monitored fish behavior at two study sites (small alpine river and low land river) to demonstrate the operational capability for upstream and downstream migration. Most species of fish and life stages were able to migrate in both directions. After passing the turbine no injured fish were detected.