Analysis and restoration of an ecological flow regime during the Coreius guichenoti spawning period

The development of cascade hydropower in the Yalong River has changed the hydrological regime of the river and sharply reduced the Coreius guichenoti population dwelling downstream of the JinPing II power station. In this paper, an eco-hydrological index system for C. guichenoti habitat was constructed based on Indicators of Hydrologic Alteration (IHA) and Environment Flow Components (EFC), which aimed to coordinate the processes of ecological hydrological and water temperature variations to guarantee the oviposition of C. guichenoti. The analysis revealed that the suitable rise rate and fall rate intervals, which are dimensionless parameters, were 0.05–0.10 and 0.01–0.03, respectively, during the spawning period. The rise and fall durations were both 1–2 days, the cycle of water fluctuations was 3–5 days, the flow pulse duration was 5–7 days, the flow pulse rise rate was 0.56–0.65, and the flow pulse fall rate was 0.23–0.50. Then, the Instream Flow Incremental Methodology (IFIM) method was used to calculate the ecological base flow during the C. guichenoti spawning period. Moreover, the ecological flow regime for C. guichenoti downstream of the JinPing II power station during the spawning period was determined based on eco-hydrological indicators and water temperature requirements. These results showed that the ecological flow regime could not only guarantee oviposition but also meet the drifting conditions required for eggs, and therefore, the ecological operation of diversion-type hydropower stations and cascade hydropower stations needs to be given more attention to provide suitable spawning conditions in target fish habitats.