4.2 Flow connectivity
After the impoundment of the TGD, the downstream erosion increases the discharge capacity of the river channel. The discharge capacity of the flood channel in the Zhicheng, Shashi and Jianli hydrological stations increased from 48963 m3/s, 36495 m3/s and 32068 m3/s before 2003 to 53807 m3/s, 40105 m3/s and 33080 m3/s, respectively, after 2003. However, due to the formation of the central bar at the Luoshan hydrological station, the discharge capacity of the flood channel slightly decreased from 45500 m3/s to 43723 m3/s before and after, respectively, the reservoir impounding. In addition, according to the calculation method of ecological flow (Guo, 2007), the ecological flow is approximately 15% of the annual average runoff in the middle and lower reaches of the Yangtze River. Therefore, the ecological flows of the Zhicheng, Shashi, Jianli and Luoshan hydrological stations are 2079 m3/s, 1855 m3/s, 1696 m3/s and 3019 m3/s, respectively.
From 1955 to 2015, the average annual runoff of the Shashi, Zhicheng, Jianli and Luoshan hydrological stations in the Jingjiang River was 390 billion m3, 437 billion m3, 358.6 billion m3 and 630.3 billion m3, respectively (Fig. 4). The annual runoff of the Jianli station tends to increase, which may be caused by the decrease in the diversion discharge. The runoff of the Luoshan hydrological station had no obvious change in trend before 1998 but the amount decreased slightly after 1998. However, there is no obvious trend of runoff at the Zhicheng and Shashi hydrological stations.