Author(s): Anita Moldenhauer-Roth; Oliver M. Selz; Ismail Albayrak; Felix Unterberger; Robert Michael Boes

Linked Author(s): Ismail Albayrak

Keywords: Fish downstream migration; Fish guidance; Fish protection; Electrified curved bar rack; Electrified horizontal bar rack

Abstract: Downstream moving fish may have to pass through turbines or spillways of run-of-river hydropower plants, which can result in life-threatening injuries and thereby impact whole populations or species. Fish guidance structures such as a vertical curved-bar rack (CBR) or horizontal bar rack (HBR) in combination with a bypass can safely guide many fish species and different life stage (i.e. sizes) around hydropower plants, thereby providing a safe downstream fish passage route. An HBR acts as a physical barrier for the fish due to narrow bar spacings, while a CBR creates turbulent structures in front of the rack, inducing a behavioral fish guidance and protection effect. HBRs with a bar spacing of 20 mm and CBRs with a bar spacing of 50 mm have shown high protection and guidance efficiencies in laboratory experiments for certain fish sizes and species. However, due to their narrow bar spacing and resulting clogging and maintenance needs, HBRs are currently state-of-the art only at small-to-medium sized hydropower plants. Combining an HBR with a low voltage electric field (e-HBR) may permit the use of larger bar spacings, thereby reducing operational issues while maintaining high protection efficiencies. Also, although a CBR with 50 mm bar spacing showed high protection rates for two cyprinid species in laboratory experiments, European eel (Anguilla anguilla) and brown trout (Salmo trutta) were less receptive to hydraulic cues resulting in lower protection rates. Hence, an electrified CBR (e-CBR) may improve the protection efficiency for these and possibly other species. In the present study, the electric fields generated by different electrode setups of both an e-HBR and an e-CBR were numerically simulated to determine suitable configurations. Subsequently, those configurations of e-HBR and e-CBR were tested with European eel in a large laboratory flume at ETH Zurich. The electric fields created by the racks were measured to validate the simulations, and the fish response was analyzed in terms of the local electric field characteristics. Both e-HBR and e-CBR protected most tested European eel, while fish bypass passage was reduced compared to the non – electrified racks. Bypass passage and protection efficiencies were not affected by the approach flow velocity varying from 0.15 m/s to 0.6 m/s. The present contribution will give an overview on fish protection and guidance technologies as well as detailed information on electrified fish guidance racks. The experimental laboratory set-up and the results of the ethohydraulic tests with European eels, in particular their behavior when confronted with an electric field, will be presented. Electrified fish guidance racks may emerge to be a cost-effective alternative to the current state-of-the art technologies.

DOI: https://doi.org/10.3850/IAHR-39WC25217119202292

Year: 2022