Comparison of electrified vertical trash racks—electric field and effects on species-specific fish behaviours

Retrofitting existing trash racks at hydropower intakes with electricity may prevent turbine passages of downstream moving fish and allow them to search for an alternative passageway if the installation of fish guidance racks is not feasible. The present study evaluated two types of electrification: (1) using the rack as an electrode and placing an additional row of electrodes downstream and (2) vertical rod electrodes placed either on the front of the bars of the rack, or used individually without combination with a bar rack. We evaluated their fish protection efficiency for a large bar spacing of 90 mm typical for large hydropower plants. Experiments were conducted with wild caught brown trout (<em>Salmo trutta</em>), chub (<em>Squalius cephalus</em>), and European eel (<em>Anguilla anguilla</em>) at approach flow velocities of 0.15, 0.3, and 0.6 m/s. For the large bar spacing tested here, placing an electrode downstream of the rack proved to be more effective than rod electrodes with protection efficiencies of 78–91% for eel and 78–95% for chub depending on the approach flow velocity. Brown trout reacted less sensibly to electric fields than chub and eel and proved difficult to prevent from rack passage.