Author(s): Md. Sajjad Hossain Tusher; Christopher Schuckers; Md. Shoriful Islam; Tom A. Langen; Haitham Ghamry; Christos Katopodis; Abul Bm Baki

Linked Author(s): Haitham Ghamry, Christos Katopodis, Abul Baki

Keywords: Rock ramp; Rock weir; Fish passage; Resting time; EDP; Stream restoration

Abstract: Improving fish passage remains a core objective in sustainable river restoration design. This study evaluated the behavioral responses of juvenile Atlantic salmon (Salmo salar) with group size (1, 4, and 6 fish) within rock-ramp and rock-weir nature-like fishways under controlled flow conditions. Salmon consistently used wake zones behind boulders for resting, with mean resting durations of 24–31 s in these sheltered regions, and the intermediate boulder density in rock-ramp-1 type configuration yielded the highest downstream passage efficiency (83–100%) across all group sizes. A composite index—Effective Downstream Passage (EDP)— was developed to assess overall performance by integrating passage efficiency, resting time, and near-bed Reynolds shear stress. Among all treatments, rock-ramp-1 achieved the highest EDP score of 0.65, indicating an optimal balance of hydraulic complexity and biological performance. These findings support the use of EDP as a decision-support tool for designing fish -friendly instream structures.

DOI: https://doi.org/10.64697/iahr.proc.ise2026.abs.135

Year: 2026