Abstract: Hydropower development impacts the habitat of migratory fishes significantly. Predicting the upstream migrating passage of target fish in their migration period can provide a basis for construction of fishway facilities so as to mitigate the negative effects. This study selects a research area in the reach downstream from the Huduxi hydropower-navigation project, takes Leptobotia elongate, Onychostoma sima and Gobiobotia bouleugeri as the target fish, and divides the study area into flow zones of different velocities by the swimming performance of these fishes. We obtain flow velocity suitability curves suitable for different fish-passing targets, and numerically simulate typical flow rates in the study area in the fish-passing period. Then, based on the suitability curves, we can evaluate the flow velocity suitability of different fish-passing targets for the study area, and use the evaluations to predict an upstream migrating channel that satisfies the multi-target fish-passing conditions. The results show that the location of fish passage optimized through flow velocity suitability evaluation varies with the channel flow rate. It goes through the mainstream zone under low-flow conditions, while through both sides of the mainstream zone under high-flows. And the proportion of the passage area to the total area also varies with the flow rate, with its low-flow values about 3 to 4 times its high-flow values. By the fish migrating channel predicted in this study, we make suggestions to optimize the layout of fishway inlet and the operation and dispatching of the power station, providing a basis for protecting the related fishes.

Key words: ecological hydraulics, flow velocity, multi-target fish, upstream migrating channel