Abstract:

In order to analyze the impact characteristics of the Three Gorges Reservoir operation process on the ecological flow and ecological effects of three outlets of the Jingjiang River, we use daily flow data of Xinjiangkou, Shadaoguan, Mituo Temple, Kangjiagang, and Guanjiapu, which are the main five hydrological control stations in the three outlets of the Jingjiang River, from 1988 to 2020. The changes in ecological surplus and ecological deficit indicators are calculated using the flow duration curve (FDC), and the overall hydrological variability D₀ is calculated to evaluate the ecological runoff and hydrological change characteristics of the three outlets of the Jingjiang River. The research results indicate that: (1) after the operation of the Three Gorges, the proportion of Songzi in the flow of Jingjiang River flowing into Dongting Lake continues to increase, while the proportion of Ouchi and Taiping continues to decrease; the annual and flood season flow rates at Ouchi and Taiping show a significant downward trend; during the dry season, the flow rate at Songzi increases by 2.5 times compared to its natural state.(2) The average number of days of zero flow at Kangjiagang Station has increased by 30.88 days, showing an increasing trend, while at Mituo, it has decreased by 21.62 days, showing a decreasing trend.(3) After the operation of the Three Gorges, the overall FDC curve decreased, especially in the upper part, with a significant decrease in the magnitude and frequency of high flow rates; except for the low flow area of FDC at Xinjiangkou Station in Songzikou which exceeds the area before the operation of the Three Gorges, other stations with high and low flow cannot fully cover the areas where high and low flow occurred before the operation of the Three Gorges.(4) Due to the continuous decrease in the proportion of Kangjiagang and Guanjiapu in the flow from Ouchi to Dongting Lake, and the continuous increase in the proportion of Guanjiapu, the Kangjiagang and Guanjiapu stations continued to experience ecological deficits and surplus from 2003 to 2020.(5) The changes in the Xinjiangkou Station at Songzikou during the trial operation of the Three Gorges Reservoir (2003-2008) and after the trial operation of the Three Gorges Reservoir (2009-2020) reached 66.68% and 72.46%, indicating a obvious change, while the remaining control stations showed moderate changes. The operation of the Three Gorges has led to long-term ecological deficits or surplus in some areas, which is not conducive to the river ecosystem. It is recommended that basin managers strengthen monitoring of changes in the diversion ratio of different branches at the same outlet and carry out corresponding ecological impact management work.

Key words: ecological surplus, ecological deficit, range of variability approach (RVA), hydrological change, Three Gorges operation, three outlets of Jingjiang