Author(s): Maximilian Kastinger; Ismail Albayrak; Luiz G. M. Silva; Robert M. Boes

Linked Author(s): Ismail Albayrak, Luiz G Martins da Silva, Robert Boes

Keywords: Downstream fish passage; Fish protection and guidance; Bypass system; Bypass passage efficiency; Ethohydraulic tests

Abstract: Fish guidance racks with adjacent bypass systems (FGR-BSs) are effective solutions for safe downstream passage at hydropower plants for many fish species. However, the bypass discharge is usually lost for electricity production because it reduces the available turbine discharge. Therefore, a gate with local openings is often installed at the bypass inlet to regulate bypass discharge. However, the spatial concentration of flow at the openings results in high flow velocities and velocity gradients that may affect the movement behavior of approaching fish. To investigate fish passage at a bypass gate with a bottom opening, ethohydraulic tests were conducted with common barbel (Barbus barbus) and brown trout (Salmo trutta) at three different approach flow velocities Uo. Velocity measurements confirmed the strong acceleration of flow in the vicinity of the opening, which often led to avoidance reactions in both fish species. Barbel showed a greater avoidance to high velocity zones compared to trout. Maximum bypass passage efficiency (BPE) was 52% for barbel at Uo = 0.3 m/s, also resulting in a higher average passage rate compared to the other approach flow velocities. Trout exhibited a similar BPE for all tested configurations, with a maximum BPE of 59% at Uo = 0.4 m/s. However, at increased Uo, bypass passage occurred faster. These results illustrate that bypass inlet gates can affect bypass acceptance and thus fish guidance efficiency of the entire FGR-BS. Further quantification of the effect of the bypass inlet geometry on bypass acceptance is crucial for a proper design of these structures.

DOI: https://doi.org/10.3850/978-90-833476-1-5_iahr40wc-p0082-cd

Year: 2023