Abstract: For the purpose of protecting fishes, the ecological base flow process of hydropower projects on mountainous rivers was studied by taking into account the Prenant's schizothoracin spawning requirements. On the basis of prototype observation and by using the ecological hydraulic method and habitat simulation method, the determination method of this kind of ecological base flow process was established. The established method was applied and analyzed by using the Xuecheng Hydropower Station on the Zagunao River as the background which is a medium mountainous river in Sichuan Province. By using the prototype observation method, the suitability of the standards for hydraulic parameters of fish habitats was analyzed. By using the ecological hydraulic method, the hydraulic parameters of fish habitats at the water reducing reach of the Xuecheng Hydropower Station at different flow rates were numerically simulated. In this paper, 11 conditions were taken into consideration, including a site investigation condition and 10 simulation conditions of different flow conditions. The investigation reflected hydrological conditions and habitat characteristics of actual situation, and provided a comparison to simulation conditions. And the concentration of spawning period of fish was selected as the investigation period. According to the simulation results and in combination with the standards for hydraulic parameters of fish habitats, the minimum discharge volume for the survival of fishes in the Xuecheng Hydropower Station was obtained. The minimum discharge volume was 17.43 m³/s, if the flow is lower than this number, the quality of fish habitat would be affected. By using the habitat simulation method, the available habitat area of the centralized spawning site in the water reducing reach of the Xuecheng Hydropower Station at different flow rates during the spawning period was calculated, and the discharge volume corresponding to the maximum available habitat area was obtained. When the peak flow in river coursed at 20.91 m³/s, the WUA of fishing spawning area in the Xuecheng Hydropower Station would be maximized. When the flow was less than 20.91 m³/s, the WUA would reduce. By integrating the minimum discharge volume and the discharge volume corresponding to the maximum available habitat area and by considering the requirements of hydrological regime required by spawning, the ecological base flow process required for the spawning was established for the Xuecheng Hydropower Station. Due to the consideration of the requirements of minimum flow rate by fish survival and the requirements of hydrological regime by spawning, the established ecological base flow process of hydropower projects which takes into account the spawning requirements can better meet the spawning requirements of fishes, and can be used as the constraints for the operation and dispatching of a hydropower station.

Key words: Prenant's schizothoracin, spawning requirements of fishes, ecological base flow process, ecological hydraulics method, habitat simulation method, Zagunao River