Identifying operation scenarios to optimize attraction flow near fishway entrances for endemic fishes on the Tibetan Plateau of China to match their swimming characteristics: A case study

Attracting fish at fishway entrances is vital for ensuring fish passage efficiency, which requires consideration of the swimming characteristics of fish. The objective of this case study was to propose optimized flow conditions downstream of a dam on the Tibetan Plateau to attract fish into fishways. Six local endemic species of Cyprinidae: Schizothoracinae were considered as protection targets. However, the swimming abilities of most endemic fishes on the plateau remain unclear, and no previous projects in this area could serve as a reference. Thus, the swimming performances of the target species were first tested based on three indexes, induction velocity, critical swimming speed and bursting swimming speed, and six behavior zones were classified by different flow velocity thresholds based on the test results. A verified 3D hydrodynamic model was then adopted to simulate the flow field downstream of the dam under four typical reservoir operation scenarios. By matching the simulated flow fields to the different behavior zones, all scenarios were assessed for the passability of the target fishes, and the results showed that there would be different potential migration routes under each scenario. For the most common scenario during the fish passage season, symmetrical use of turbines T1 and T6 was recommended so that the flow would be lower velocity and the turbulence would be less intense near the fishway entrances than the current regime. Moreover, the addition of a new entrance was suggested on the migration routes with high potential use to increase the chance that fish would enter. Beyond providing a solution for this specific case, this study enriches knowledge about the swimming features of endemic fishes on the Tibetan Plateau. Furthermore, this research provides a possible technical methodology that combines fish behavioral characteristics and hydraulic indexes when determining attraction flows in similar fish passage projects.