Author(s): Ana T. Silva; David Aldven; Stephanie Muller Muller; Eric Lilleberg; Kamal Pandey; David F. Vetsch; Olle Calles; Robert M. Boes; Torbjorn Forseth; Ismail Albayrak

Linked Author(s): David Aldvén, Ismail Albayrak

Keywords: Downstream migration; Behaviour fish guidance; Mitigation measures; Salmo salar

Abstract: Effective downstream fish passage remains a significant challenge for large hydropower plants (HPPs), with crucial implications for freshwater biodiversity and the conservation of migratory species like Atlantic salmon (Salmo salar). The FishPath project addressed this issue by developing an innovative, behavior-based Eddy- Guidance System (EGS) designed to guide fish away from turbine intakes and toward safer migration routes. The system exploits turbulent eddies, which fish can use for orientation, energy -efficient swimming, or avoidance. In the FishPath project, various types of eddies (horizontal, vertical, and streamwise) were created using eddy generators, and their effects on fish behavior were tested under controlled laboratory conditions at VAW, ETH Zurich. Streamwise eddies were found to be particularly effective in guiding Atlantic salmon smolts (Pandey et al., 2026). This finding supported the design and testing of an EGS, which consisted of streamwise eddy generators attached to vertical NACA profiles (elements). This EGS was tested with live fish in spring 2024 at a medium-scale flume at VAW, ETH Zurich, and demonstrated high guidance efficiency. The effectiveness of the guidance strongly depended on the space between elements and the angle of the EGS relative to the approach flow, with fish guidance efficiencies ranging from 44-66% to 73-97% at lowest and highest angle, respectively. The most promising EGS design was scaled up and further tested with Atlantic salmon smolts in spring 2025 in the Laxeleratorn flume (24m x 4m x 2m) at the Vattenfall R&D laboratory in Älvkarleby, Sweden. In total, two sizes of the eddy generators and two different spacing configurations between elements were tested for four approach velocities. High guidance efficiency was achieved, reaching 87-100% with the medium element ( smaller eddie generators) and larger spacing between elements. Water velocity also influenced guidance efficiency. The results suggest that the EGS is a highly promising solution for protecting and guiding Atlantic salmon smolts, as well as other species with similar biomechanics and behavior.

DOI: https://doi.org/10.64697/iahr.proc.ise2026.abs.274

Year: 2026