Spatiotemporal Evolution of Erosion and Deposition in the Current Yellow River Estuary Under Different Water and Sediment Regimes

The ecological water regulation in spring and the occurrence of two rare floods in the area of the Yellow River Estuary from 2018 to 2021 led to the changes in water and sediment flux and process. In order to know the changes in geomorphological characteristics in the coastal area of the estuary, the changes of 2 m, 5 m and 10 m isobaths, the evolution of erosion and deposition, as well as the development of delta fronts of each branch of the current estuary are analyzed and compared, according to the measured bathymetric data and combined with the water and sediment data of Lijin Hydrological Station in the same period. The results show that the average annual amount of water and sediment delivered into the sea from 2018 to 2021 is 36.2 billion m³ and 281 million tons respectively, being twice of that from 2002 to 2017. In the 4-year period a total of sediment delivered into the sea is 1,167 billion tons (including 42 million tons from the tail river channel erosion), of which approximately 858 million tons (about 613 million m³) of the sediment are deposited in the coastal area of the current estuary. At the flood time the flood peak flows into the sea in the form of diffuse flow and the stability of the tributary mouths is weakened. As a result, the branching and oscillating evolution of the estuary is accelerated and an elliptical, continuous and narrow silting zone with its horizontal axis parallel to the shoreline and its short axis vertical to the shoreline is formed in front of the tributary mouths. The delta fronts are fully developed due to the sufficient water and sediment supply. During great flood, the estuary can naturally branch in the northeast and the east branch and the northeast branch become the main branches into the sea.