Study on the evolution of ecological flow in river and its guarantee degree during different hydrological periods

Determining the ecological flow of rivers presents significant challenges due to their poor adaptability to varying hydrological regimes and general overlooking of aquatic organisms’ life rhythms in response to hydrological characteristics. To address these issues, this study proposes a novel approach, the 7Q dynamic frequency method, which calculates ecological flow by integrating basic and characteristic hydrological frequencies, based on the dynamic stability criterion of flow over seven consecutive days. The hydrological data used for the calculations is derived from the natural runoff restored by the Sliding-GRU model, with the previous period treated as the natural period based on the division of hydrological periods determined through hydrological mutation analysis. Furthermore, the health status of the river is assessed by the ecological flow guarantee rate at different time scales, after evaluating the suitability of the 7Q dynamic frequency method through the construction of an evaluation system. Taking the lower reaches of the Fuhe River as the study area, the results indicate that the flow series of the river can be divided into four hydrological periods with an overall low degree of hydrological alteration. The ecological flows calculated for each hydrological period using the 7Q dynamic frequency method are both reliable and highly suitable for the river’s hydrological characteristics, ensuring the basic water conditions of the river ecosystem. Overall, the guarantee degree of ecological flow in the river is low, decreasing from the natural period to the impact period, with an upward trend during the transition period. Moreover, the long-term guarantee rate is higher than the short-term guarantee rate across all hydrological periods. This study provides valuable theoretical and methodological support for the scientific determination of ecological flow.