Changes in dominant discharge and their influential factors in the middle and lower reaches of Yangtze River after the Three Gorges Dam impoundment

With the impoundment of the Three Gorges Dam (TGD), the dominant discharge in the reaches downstream of the TGD have changed. Studying the changes in dominant discharge and the factors driving these changes is of great importance to illustrating the changes and mechanisms of riverbed evolution in the downstream reaches. Based on data from 1981 to 2015, the Makayev method, frequency analysis and the bankfull level method are used to calculate the pre-and post-dam dominant discharge in Yichang, Zhicheng, Shashi, Jianli, Luoshan, Hankou, Jiujiang and Datong. The results show the following:① Both the flow process and sediment transport capacity are taken into account by the Makayev method, and the results are relatively reasonable. ② The post-dam dominate discharge at each station is reduced by 3 000-6 000 m³/s and is consistent with the adjustment area changing from bankfull channel to medium flow channel, which reflects the rationality of the results. Specifically, through time, the dominate discharge decreases clearly after 2009; spatially, the dominant discharge decreases from Yichang to Jianli and then increases from Jianli to Datong. ③ The dominate discharge is sensitive to the runoff of the incoming flow and peak discharge, and this relation exhibits a positive correlation.