The FishProtector consists of many horizontally tensioned steel cables with a certain distance between them, which are tensioned over the whole flow cross section at the intake area of a hydropower plant. It is a hybrid system which optimizes the function of fish guiding and fish deterring. The steel cables, representing the mechanical component of the hybrid system, also act as anodes and cathodes and guiding towards the bypass due to their orientation. The applied electrical current is in the low voltage range and thus harmless for humans and animals alike and can be varied according to the actual requirements. The electrical field, the behavioural barrier of the hybrid system, has a deterring effect on the fish (fig. 1). The bigger a fish, the better it perceives the electrical field.

The system of the FishProtector has been developed at the University of Innsbruck and been evaluated considering its´ technical feasibility and its´ fish protection and guiding potential in extensive scientific projects in cooperation with national and international partners from science (Unit of Applied Mechanics Universität Innsbruck, Institute for Hydrobiology and Aquatic Ecosystems Universität für Bodenkultur in Vienna (BOKU)) and economy (Fa. Albatros Engineering GmbH in Austria, IUS Weibel & Ness GmbH in Germany, Procom System S.A. in Poland) [1].

The great advantage of the PishProtector is that the clear distances between the cables can be considerably greater compared to conventional screens or racks. The fish, which would easily be able to pass through the barrier due to their size, are prevented from a passage by the created electrical field and guided towards the bypass by the orientation of the FishProtector.

Another advantage of the systems is, next to the reduced constructional effort, the reduced hydraulic losses caused by the circular shape of the cables, the great clear distances between cables and the missing of struts or spacers.

The FishProtector can be installed at hydropower plants of any size. Cable lengths of more than 100 m are technically feasible [2].

While approaching, fish still perceive the mechanical barrier despite the great clear distances (e.g. 60 mm). Then, they typically position their body against the flow direction (head facing upstream). In a further careful approach to the FishProtector they perceive the electric field in quite a distance to the steel cables and show a controlled escape reaction in upstream direction respectively according to the angle of incidence of the cables parallel towards the bypass (fig. 2). The special fish behaviour is caused by the hybrid protection effect of the FishProtector [1].

 In comparison to rigid horizontal racks (consisting of bars) the flexible structure of the FishProtector enables an advantageous operational mode for screen cleaning by de-tensioning/releasing of single cables or even clusters of cables.

During regular operation, all cables are fully tensioned (fig. 3-1).

In the case of local clogging by floating matter (foliage, grass, branches and suchlike) single cables or cable clusters can be released in order to re-mobilize the material on the screen surface. The flotsam is transported right over the power house at overflowed power plants respectively collected at the screen cleaning system at regular plants (fig. 3-2).

At increased discharge, the cables are collectively lowered to the river bed and the whole flow cross section area is released for discharge and sediments of any kind. Consequently, the entire screen surface can be cleaned and prevented from clogging by partially or entirely releasing the cables (fig. 3-3).

Literature: