The analysis of water exchange regime research on Poyang Lake and Yangtze River and driving factors

In Yangtze river basin, the interaction of mid-lower stream of river and lake is becoming increasingly complex nowadays because the dam construction and the reservoir operation upstream are changing the natural coming water condition. Based on the water exchange process analysis of Yangtze River and Poyang lake in which the Poyang lake diverts flood from Yangtze river in flood season and replenishes water in dry season, three indexes are defined to quantify the water exchange characterization and monthly variation of the Yangtze River and Poyang Lake, i.e., the index of jacking strength (JSI), the index of intruding strength (ISI) and the coefficient of water exchange (WEC). The method of trend-free pre-whitening Mann-Kendall (TFPW-MK) is employed to analysis the trend of annual water exchange as well as the Mann-Kendall (MK) method. The regime of river-lake water interaction are revealed in perspectives of the difference of coming water, the operation of the Three Gorges reservoir and the stage-capacity variation of Poyang lake. Results show that the flood from Yangtze River diverting to Poyang Lake is the major state during flood season (July to September), the annual mean JSI is 27.5% with a frequently intruding phenomenon (the average ISI is 8.3%); the water from Poyang lake flowing into Yangtze River is the major state during non-flood season (December to April) with the annual mean JSI 8.8%. After the Three Gorges being put into operation since 2003, the flow of mid-lower Yangtze River increased during the period of December to March with a JSI enlarged by 6% at Hukou station; the peak clipping effect of the Three Gorges in the flood season weakened the jacking strength and intruding strength by 4.8% and 2.3%, respectively. Also the average annual JSI is further deceased 0.14% due to the capacity evolution of the Poyang Lake in the past 20 years. The differences of coming water from Yangtze River and Poyang Lake is the dominant factor which drives the evolution of river-lake interaction. This research explored the water exchange regime of Yangtze River and Poyang Lake which could be used as a reference for the comprehensive management of Poyang Lake.