Runoff variation in the middle and lower branches of Yangtze River and the two lakes (Dongting and Poyang Lake) before and after Three Gorges Reservoir's operation

Abstract

为探索三峡水库运行前后长江中下游干流及两湖径流过程的变化及其驱动因素,利用宜昌、监利、大通、七里山、湖口共5个水文站的流量资料,分析了各站径流过程的变化特征及其成因。结论:(1)各站年径流量均减少,但除七里山站之外,其它各站减少比例均小于10%且变化不显著;(2)干流各站月径流量最大减幅发生在10月,而七里山站、湖口站分别发生在7月、4月;(3)干流各站月径流量最大增幅发生在3月,而七里山站、湖口站分别发生在1月、6月;(4)宜昌站,1-4月径流量增加是三峡水库入库径流增加和水库调度的共同作用结果,6-8月径流量减少的主因是三峡水库入库径流量减少,5、9、10月径流量变化的主因是三峡水库调度;(5)监利站,径流量的变化与宜昌站表现出高度的一致性,但冬季各月径流量的增幅均大于宜昌站;(6)大通站,4-6月径流量变化方向与湖口站一致,其它月份变化方向均与宜昌站一致。(7)七里山站,7月径流量减少的主因是洞庭湖流域来水减少,9、10月径流量减少的主要原因是荆江分流减少,但洞庭湖流域来水减少也是重要原因。(8)湖口站,4、5月径流量减少的主因是流域降水减少,9、10月径流量减少的主要原因是鄱阳湖汛期水位降低、低水位提前、蓄水量减少。;To explore and explain the changes of runoff process in the middle and lower Yangtze River mainstream and the two lakes of Dongting and Poyang before and after the operation of the Three Gorges Reservoir (TGR), the runoff data of five hydrological stations, which are Yichang, Jianli, Datong, Qilishan, and Hukou, were used. The stations of Yichang, Jianli, and Datong locate along the mainstream of the Yangtze River, while the other two stations locate at the exit of the Dongting and Poyang Lake, respectively. The runoff changes at each station before and after the TGR's operation and its causes were analyzed. Conclusions include: (1) The annual runoff at each station decreased, except at Qilishan Station, the reduction ratio of runoff at other stations was less than 10% and their changes were not significant; (2) The maximum decrease in monthly runoff at each mainstream station occurred in October, except that at Qilishan Station and Hukou Station it occurred in July and April, respectively; (3) The maximum increase in monthly runoff at each mainstream station occurred in March, while at Qilishan Station and Hukou Station it occurred in January and June, respectively; (4) At Yichang Station, the increase of monthly runoff from January to April resulted from both the inflow increment of the TGR and its operation. The main reason for the decrease in monthly runoff from June to August was the decrease in the inflow of the TGR. The main reason for the runoff change in May, September and October was the operation of the TGR; (5) At Jianli Station, the change of runoff was highly consistent with that at Yichang Station, but the increase of runoff at Jianli Station in each month in winter was greater than that at Yichang Station; (6) At Datong Station, from April to June the change direction of monthly runoff was the same as that at Hukou Station, and the change direction of other months was the same as that at Yichang Station. (7) At Qilishan Station, the main reason for the runoff reductions in July was the reduction of rainfall in Lake Dongting basin, and while the reduction of the diversion from Jingjiang River is the main cause to the runoff reduction in September and October, the reduction of rainfall in Lake Dongting basin also played an important role; (8) At Hukou Station, the decreases in runoff in April and May resulted from the reduction of rainfall in Lake Poyang basin, while the main reason for the runoff decreases in September and October was the reduction of water level in Lake Poyang during the previous months, which led to the early low water level season and the reduction of water storage.