Downstream-migrating fish in rivers tend to follow the main current, and are in danger of swimming through the turbines at run-of-river hydropower plants, possibly causing high mortality rates. To avoid these losses, fish must be prevented from entering the turbines. Most existing vertical bar rack systems (used for turbine protection) however usually do not ensure proper fish protection due to large bar spacings. FishProtector technology enables the retrofitting of existing bar racks (i.e., the mechanical barrier) with additional electrodes to create a hybrid barrier. The induced electric field in the water aims to create a behavioral barrier to prevent fish passage through the bar rack. In this study, ethohydraulic experiments to investigate the effect of such a behavioral barrier on fish were performed. In detail, the fish-protection rate at a bar rack with a bar spacing of 30 mm was tested in five different scenarios: (i) a bar rack without electrodes (reference), and four electrified setups with electrode spacings of (ii) 80 mm, (iii) 120 mm, (iv) 160 mm, and (v) 200 mm. A flow velocity of 0.23 m/s was chosen to replicate the situation at a planned pilot site. The study was conducted in an outdoor laboratory flume using small fish of several local riverine species, mostly cyprinids and minnows. The results show that the mean fish-protection rate in the experiments could be increased from 62% in the reference setup up to 96% in the electrified setups.

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Bar racks at water intakes of hydropower plants serve mainly to protect the turbines from floating debris. Additionally, they can be utilized to protect downstream migrating fish in order to prevent a potentially harmful turbine passage. The Bar Rack FishProtector consists of a common bar rack equipped with electrodes mounted on the upstream side of the bars. The application of a low voltage current at the electrodes creates an electric field in the water which is actively avoided by fish. Thus, a hybrid barrier consisting of a mechanical barrier and a behavioral barrier is formed. An unscaled model of a Bar Rack FishProtector (bar spacing sb = 50 mm, bar thickness tb = 20 mm) was used in field experiments to investigate the retention rate in an experimental setup with only one possible migration route (downstream, rack passage) and an average flow velocity of 0.43 m/s. Ethohydraulic experiments were performed with three indicator species barbel (Barbus barbus), bream (Abramis brama) and roach (Rutilus rutilus) and additionally perch (Perca fluviatilis) in selected trials. The twelve trials included four reference trials without electric field present (Nday = 2, Nnight = 2) and eight trials with electric field (Nday = 6, Nnight = 2). The results show that the experimental retention rate could be increased significantly by the application of an electrical field during the night and during the day with an even more pronounced effect during the night. The differences between the functionality of the system during the day and at night as well as other influencing parameters are discussed. No significant influence of the applied voltage on the electrodes or significant influence of fish size could be identified.

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