River Regime Evolution of the South Channel in the Changjiang River Estuary, China, During Past 50 Years

As the middle reach of the Changjiang River Estuary, China, the South Channel’s evolution would directly affected upper and lower reaches. However in recent decades, fluvial water and sediment loads have appeared notable changes, consequently, the latest evolution of the South Channel would adjust either. Hence, topography data of the South Channel in different historical period during past 50 years were adopted, then geomorphology evolution were analyzed in detail. The result showed that river regime of the South Channel had undergone three stages. In the first stage among 1973~1981, it deposited 1.0~9.7 m in central shoal and eroded −1.0~−13.6 m in two side deep channels. In the second stage during 1981~1994, the erosion and sedimentation region turned around, wherein the central shoal eroded −1.0~−9.8 m and two side channels deposited 1.0~10.6 m. In the third stage during 1994~2016, the central shoal partially deposited 1.0~8.1 m and partially eroded −1~−6.1 m, and both side channels eroded −1~−13.2 m. Meanwhile, in the inlet cross section during 1973~2016, location of main channel moved 275 m southward with average elevation changing −1.1 m and the central shoal eroded about −4.6 m. In the middle and outlet cross sections, their central shoal eroded −1.3~−5.8 m and main channel respectively swung 450 m northward with elevation decreasing 0.4 m and 1775 m northward with elevation deepening 6.1 m. Moreover, average elevation of thalwegs changed from −14.0 m to −15.9 m during 1973~2016. Furthermore, evolution characteristics of geomorphology and fluvial water and sediment load in past 50 years showed that there might be close relationship between them.