5.2 Construction of the TGR
Since the impoundment of the TGR, river channel erosion is serious downstream of the dam (Fig. 9a, Fig. 9b). From 2002 to 2015, the scouring volume of the Jingjiang River was 0.71 billion m3, with an average erosion volume of 0.05 billion m3/a (Fig. 9a). It is far greater than the average erosion of 0.0137 billion m3/a from 1972-2002. The riverbank collapse of the Jingjiang River occurs frequently due to channel erosion. From 2003 to 2012, there were 654 bank collapses in the middle and lower reaches of the Yangtze River, with a total length of 495.9 km. After bank failure, the bank will retreat gradually, and the area of the section will increase (Fig. 9c), which will improve the channel connectivity.
In the Zhicheng-Shashi reach and Shashi-Jianli reach, the function value of channel connectivity ranged from 0.9 to 1.0 from 1990-2002; however, the value gradually increased and was basically greater than 1.0 after 2003, indicating that the construction of the reservoir improved the downstream channel connectivity (Fig. 8). The channel connectivity does not change in the Jianli-Luoshan reach since the impoundment of the TGR because it is located far from the dam.