Fig. 1. Important locations and geographical features of the Yangtze Estuary. (a) Locations of the Datong station, the Three Gorges Dam (TGD), the Gezhou Dam (GZD) and the Danjiangkou Dam (DJKD) within the Yangtze River Basin of China, and the Yangtze Estuary (the study area); (b) plan view of the Yangtze Estuary; CES, HES and NES represent Chongming East Shoal, Hengsha East Shoal and Nanhui East Shoal, respectively; the region enclosed by the red line almost covers the entire Yangtze Estuary downstream of Xuliujing, which is identical to that in Chen Y et al. (2018) providing the major dataset of total erosional/depositional rate in this study; (c) major sediment sources of the Yangtze Estuary.

Fig. 2. Comparison between morphological and hydrological processes in the Yangtze Estuary. (a) Histogram of erosional/depositional rates (positive values indicating deposition, and negative ones representing erosion) of the marked submerged area (Figure 1b) in the periods of 1950-1958, 1958-1983, 1983-1997, 1997-2002, 2002-2009, 2009-2013 and 2013-2015, respectively; dashed arrow during 1950-1958 represents an erosional state of the marked submerged area and red-bold line segment over 1983-1997 stands for an equilibrium state. (b) Yearly river water discharge, D_≥60,000 and yearly and multi-year average river sediment load at Datong from 1950 to 2015.

Fig. 3. Residual water level changing with distance upstream from the Yangtze River mouth with varying monthly river water discharge in 2005.

Fig. 4. Yearly dredging amount of the Deepwater Channel Project from 2000 to 2015 (a) and multi-year average reclamation rates over the whole Yangtze Estuary during the periods of 1960-1980, 1980-2000, 2000-2010 and 2010-2015 (b) and erosional/depositional rates (positive values indicating deposition, and negative ones representing erosion) of the entire Yangtze Estuary during the comparative periods ((a) and (b)).

Fig. 5. Spatial distribution of bed-elevation changing rates (positive values indicating deposition, and negative ones representing erosion) in the Yangtze mouth bar area (121.78°E-122.34°E, 30.96°N-31.46°N) during the periods of (a) 1997-2002 and (b) 2002-2007

Fig. 6. Comparison of net sediment supplies at Xuliujing and the Yangtze River mouth with depositional rates within (a) Area 1, (b) Area 2 and (c) Area 3 during 2002-2009. Specifically, Area 1 represents the mouth bar area (121.78°E-122.34°E, 30.96°N-31.46°N) in Figure 5, Area 2 the submerged delta (121.78°E-122.67°E, 30.82°N- 31.53°N) in Dai et al. (2014a), and Area 3 the large submerged area of the entire Yangtze Estuary downstream of Xuliujing in Chen Y et al. (2018). In addition, the blue numbers represent the net sediment fluxes at Xuliujing and the Yangtze River mouth, whereas the magenta numbers indicate the depositional rates of the three areas.

Fig. 7. Histogram of multi-year average duration days at different levels of river water discharge at Datong during different stages of the construction of major dams on the Yangtze River. The dividing years of 1968, 1981 and 2003 represent the start years of water impoundment of Danjiangkou Dam, Gezhou Dam and Three Gorges Dam (Figure 1a) respectively.

Fig. 8. Variations in sediment sources of (a) the Yangtze River Basin, (b) the Yellow River Delta and (c) the Hangzhou Bay, and the consequent morphological change rate of the entire Yangtze Estuary in the future.