Abstract: In recent years, the ecological flow in the three outlets rivers of the middle Yangtze River into Dongting Lake area is in severe shortage due to the construction and operation of large hydropower projects, the continuous reduction of diversion discharge of the three major outlets rivers, and the unreasonable utilization of water resources. We propose a method to determine the ecological basic flow by comprehensively considering the calculated results of different hydrological methods based on daily discharge data of main hydrological stations from 2003 to 2018 and monthly average discharge from 1973 to 2002 in the three major outlets rivers. We further obtain the recommended values of annual and monthly ecological basic discharge and analyze the guarantee rate and influence factors. Results demonstrate that the annual ecological base flow at Xinjiangkou, Shadaoguan, Mituosi, Kangjiagang and Guanjiapu hydrological stations is 208.18 m³/s, 49.44 m³/s, 75.39 m³/s, 2.52 m³/s and 93.94 m³/s, respectively, and their corrsponding guarantee rate of ecological base flow is 84.83%, 37.52%, 51.88%, 21.84% and 42.60%, respectively. The highest monthly ecological base flow of all hydrological station appears in July, and decreases in August, September, and June in turn. The ecological base flow and its guarantee rate in flood seasons are significantly higher than those in non-flood seasons. The proposed method and calculated results could be taken as reference for aquatic ecological restoration in the Dongting Lake area.

Key words: Dongting Lake area, three major outlets river, ecological basic flow, hydrologic method, guarantee rate