Hydraulic and turbulence structure of triangular labyrinth weir‐pool fishways

Abstract

AbstractDetailed laboratory experiments were conducted to analyze and evaluate a new weir‐pool fishway design. The new design consisted of a series of one‐cycle, triangular labyrinth weirs that formed a weir‐pool fish passage. Hydraulic characteristics of flow over the proposed fishway were examined for three pool lengths and a wide range of discharges. It was found that the new design had superior discharge capacity over classical weir‐pool fishways in plunging flow regime. Spatial and point analyses of measured velocity data were carried out to understand turbulence structure and distribution of turbulent flow. The power dissipation per unit volume was calculated for different tests, and it varied nonlinearly with discharge. Based on the limiting criteria for energy dissipation rates of different fish species, the maximum operating discharge for different slopes was extracted for the proposed design. The model‐to‐prototype scaling analysis was performed based on the recommended scaling factor of three for prototype. It was found that the approach velocity of prototype increased by 12%, whereas the total discharge increased by more than five times. The contour plots of time‐averaged velocity indicated that the proposed fishways offered diversified flow fields without exceeding the maximum velocity above the standards recommended for weir‐pool fishways. To study the size, direction, and periodicity of turbulent eddies, magnitude of the most energetic eddy and dominant frequencies were extracted using power spectrum analysis. Quadrant analysis consistently showed that Reynolds shear stresses in ejection and sweep events became weaker as the pool length increased. The small region of strong ejection and sweep events evidenced a good resting place for fish migration, whereas the generated turbulence was large enough to attract fish species to use the passage.