Archimedes Screw—An Alternative for Safe Migration Through Turbines?

AbstractFish passing downstream through hydraulic structures and turbines may risk dying or getting injured. Archimedes screw turbines are frequently considered more “fishfriendly” than conventional turbines. However, to date only a handful of studies assess the impact of Archimedes screws. Within the FIThydro project, we investigated injury and mortality on 2700 bream, roach and eel, including passive barotrauma sensors passing a large Archimedes hydrodynamic screw (10 m head, 22 m length) on three rotational speeds of 30, 40 and 48 Hz. The sensors measured total water pressure, linear acceleration, rotation rate, magnetic field intensity and absolute orientation. They indicated that passage is a chaotic event, and that barotrauma-related injury and mortality are indeed unlikely. Nonetheless, substantial mortality of fish was observed, specifically for bream (42%) and roach (18%) but not for eel (1%). No straightforward relation was found between rotational speeds and fish injury and mortality. The study indicates generally lower mortality and injury rates compared to conventional turbine types. However, fish can still get heavily injured or die, depending on the fish species. Therefore, we stress the need for further studies on Archimedes screws to identify the causes of the observed species-specific injury and mortality rates.