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<p>Angled racks are widely used at water intakes, yet live-fish evidence on how approach-flow conditioning interacts with fine bar spacing to affect downstream passage of small-bodied species is scarce. We tested whether adding a curved guidance wall to an angled 10 mm fine screen improves approach hydraulics and increases bypass passage probability for the potamodromous leuciscid <i>Alburnoides kosswigi</i>, and whether screen angle (30° vs 45°) or fish length affects outcomes. Ethohydraulic flume experiments incorporated two screen angles and the presence or absence of walls, resulting in four distinct treatments across 120 individual trials. Three-dimensional velocities were mapped with acoustic Doppler velocimetry (ADV) to quantify approach hydraulics, including streamwise spatial velocity gradient (<i>SVG</i><sub><i>x</i></sub>). Passage success (bypass entry within 30 min) was analysed using binomial GLMs. With the implementation of the guidance wall, the bypass inlet velocity was reduced from 0.94 m/s to 0.65 m/s for <i>α</i> = 30°, and from 0.73 m/s to 0.65 m/s for <i>α</i> = 45°. The <i>SVG</i><sub><i>x</i></sub> values were reduced to approximately 0.1 s<sup>−1</sup> at the bypass inlet, and the normal velocities along the screen were also reduced by the guidance wall. More uniform velocity distributions towards the bypass channel were observed at <i>α</i> = 45° with the guidance wall. Consequently, bypass efficiency increased from 56% to 80% at 30° and from 63% to 90% at 45° with the wall. In models, the wall was the only robust predictor of success (OR 3.95, 95% CI 1.66–10.08), whereas angle and fish length were not significant. However, an exploratory threshold analysis suggested a tentative 96-mm cut-off above which success increased (<i>β</i> = 1.50; <i>p</i> = 0.0595). Overall, the results show that using a curved guidance wall in the conditioning approach flow can increase downstream passage by 25–30% at angled fine screens without increasing entrainment. This suggests that guidance-wall design should be considered in intake standards at poor approach-flow conditions for small-bodied potamodromous fish.</p>

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Ethohydraulic Evidence that Curved Guidance Walls Boost Bypass Efficiency of a Small-bodied Leuciscid

  • 期刊论文

  • 发表日期：

    2026年6月26日

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  • Cumhur Ozbey,
  • Serhat Kucukali,
  • Baran Yoğurtçuoğlu,
  • M. Salih Turker,
  • Ahmet Alp

摘要

Angled racks are widely used at water intakes, yet live-fish evidence on how approach-flow conditioning interacts with fine bar spacing to affect downstream passage of small-bodied species is scarce. We tested whether adding a curved guidance wall to an angled 10 mm fine screen improves approach hydraulics and increases bypass passage probability for the potamodromous leuciscid Alburnoides kosswigi, and whether screen angle (30° vs 45°) or fish length affects outcomes. Ethohydraulic flume experiments incorporated two screen angles and the presence or absence of walls, resulting in four distinct treatments across 120 individual trials. Three-dimensional velocities were mapped with acoustic Doppler velocimetry (ADV) to quantify approach hydraulics, including streamwise spatial velocity gradient (SVGx). Passage success (bypass entry within 30 min) was analysed using binomial GLMs. With the implementation of the guidance wall, the bypass inlet velocity was reduced from 0.94 m/s to 0.65 m/s for α = 30°, and from 0.73 m/s to 0.65 m/s for α = 45°. The SVGx values were reduced to approximately 0.1 s−1 at the bypass inlet, and the normal velocities along the screen were also reduced by the guidance wall. More uniform velocity distributions towards the bypass channel were observed at α = 45° with the guidance wall. Consequently, bypass efficiency increased from 56% to 80% at 30° and from 63% to 90% at 45° with the wall. In models, the wall was the only robust predictor of success (OR 3.95, 95% CI 1.66–10.08), whereas angle and fish length were not significant. However, an exploratory threshold analysis suggested a tentative 96-mm cut-off above which success increased (β = 1.50; p = 0.0595). Overall, the results show that using a curved guidance wall in the conditioning approach flow can increase downstream passage by 25–30% at angled fine screens without increasing entrainment. This suggests that guidance-wall design should be considered in intake standards at poor approach-flow conditions for small-bodied potamodromous fish.