Abstract:

Lower Jingjiang, located in the middle reaches of the Yangtze River, is one of the most unstable sections of the Yangtze River. Due to the particularity of Lower Jingjiang, the operation of the Three Gorges Project (TGP) will inevitably have a great impact on the hydrological processes of this section. Based on the daily flow data of Jianli gaging station, the annual runoff and monthly flow trends of Lower Jingjiang River were analyzed from 1983 to 2012. The runoff change of the Lower Jingjiang River caused by the TGP was extinguished from the natural fluctuation with the consideration of the operation of the project. The results showed that, the annual runoff of Lower Jingjiang was dominated by the fluctuation process and had no significant trend in the past 30 years. There were significant increasing trends of monthly flows of January, February and March, and a significant decreasing trend in October. After the impoundment of TGP, the monthly flow of the first five months in a year all increased, while that of other months decreased. The absolute change amount of monthly flow in October, July and August were the three largest in a year. The three largest months showing increasing flow were February, March and January. The relative change rate (RCR) was introduced to eliminate the natural fluctuation pattern by using the ratio between the monthly flows changes after the project operation and the standard differences of the monthly flows without TGP. The RCRs of January, February and October (all >1.5) were the greatest in a year. Although the absolute change amount of July and August were the second and third largest in a year, their RCR value was less than 1, meaning that the flow changes of these two months were less than the natural fluctuation range. Based on the previous analysis, we can know that the operation of the TGP had the most significant effect on the flow of low water period. The TGP would probably affect the shipping and drought in Lower Jingjiang River in autumn and winter. It is necessary to assess the potential impact of the flow variation upon the watersediment processes and morphological change of the river section