Abstract
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.
Highlights
In the electrified setups, fish maintained a certain distance to the bar rack
This electric field serves as a behavioral barrier complementing the bar rack as a barrier itself and creating an efficient hybrid barrier for fish protection
This study served to investigate the effect of a vertical bar rack retrofitted with electrodes to create a behavioral barrier to prevent downstream fish passage, thereby contributing to a further improvement of fish-protection technologies at water intake structures
Summary
Longitudinal connectivity plays an essential role in riverine ecosystems, and migration is an intrinsic need for the majority of aquatic organisms such as fish [1]. Fish migrate to satisfy certain needs which are not met in the current habitat; these may include the urge to reach spawning, feeding or resting habitats [2]. It is well-known that anthropogenic obstructions such as hydropower plants block instream migration routes, and the effects of habitat fragmentation are especially deleterious for potamodromous and diadromous fish species [3]. Research has focused on studying the upstream migration of fish, in particular on diadromous species [4,5]. Downstream migration, in contrast, has not been investigated to the same extent as upstream movements [4,5]
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