Figure 6 The variation in sediment load
In the Zhicheng-Shashi reach, the value of the sediment matching index was approximately 1.0 before 2003. After 2003, the index decreased significantly to below 1.0 and then decreased to 0.56 in 2015, which indicated that the river reach was scoured seriously in this period (Fig. 7a). The variation in the index is consistent with the variation in river erosion and deposition. In the Shashi-Jianli reach, the average value of the sediment matching index is 1.0 before 2003, which indicates that the riverbed elevation is basically stable. However, the index shows a decreasing trend after 2003, with an average value of 0.5, which indicates that the channel erosion is severe in this period (Fig. 7b). In the Jianli-Luoshan reach, unlike in the previous reaches, the values of the sediment matching index are basically less than 1.0 (Fig. 7c), mainly because the flow with low sediment concentration flows into the Yangtze River after the Dongting Lake regulation and storage, causing the Jianli-Loshan reach to be in the erosion state.