Abstract:
Based on the measured topographic data of the Yangtze River estuary from 1958 to 2019, these factors such as riverbed boundary, channel volume and riverbed evolution of the South Branch and the North Branch are calculated. The results show that the riverbed evolution of the South Branch and the North Branch has a certain regularity from 1958 to 2019: (1) The change of riverbed boundary shows the same trend, which follows shoreline shrinking and extending, and the river area gradually shrinking. (2) The riverbed evolution between the North Branch and the South Branch shows obvious differences. The time variation of the South Branch tends to scour as a whole with alternating between erosion and deposition and shows continuous scour since 1998, and the spatial change shows the characteristics of "beach and silting channel brush". But the North Branch tends to deposit as a whole and the river channel shrinks. (3) The change of channel volume shows a certain relativity. The total volume of the South Branch and the North Branch with +2 m deep fluctuates slightly around 8.476 billion m
3, which remains stable basically. Compared with 1958, the total volume in 2019 is only increased by 4.1%. The riverbed evolution of the South Branch and the North Branch is affected by water and sediment dynamic conditions and human engineering. With the stability of cross-section shape, shoal channel pattern and sediment inflow in the South Branch and the North Branch, their riverbed evolution tends to be balanced and stable as a whole.