On the change of coastline and underwater terrain of the southern Laizhou Bay since 1958

The coastal geomorphology of the southern coast of Laizhou Bay, Shandong, has changed greatly since the 1980s. It is of great significance to study the evolution of coastal geomorphology for coastal protection and sustainable utilization of coastal resources. We used the charts and remote sensing images measured or imaged in different periods as data sources, and quantitatively studied the coastline and offshore slope evolution based on remote sensing and GIS technology. The results show that: ① from 1958 to 2021, the natural shoreline gradually decreased and the artificial shoreline gradually increased. Until 2021, the length of artificial shoreline accounted for about 87% of the total length. Coastline evolution was closely related to the coastal construction; ② taking 1984 as the boundary, natural evolution dominated before 1984, and human activities played a leading role after 1984. Under natural evolution, the coastline was dominated by land erosion. Under human intervention, it was dominated by seaward advance; ③ the distribution of erosion and deposition on the subaqueous slope was extremely unbalanced, and the overall trend was from erosion, siltation, to slowed-down siltation. The southern river estuary was largely eroded after 1984. The 0 m and 2 m isobaths advanced or and retreated slightly. The 5～9 m isobaths advanced seaward significantly in the west of the Dihe River, and the evolution of erosion-siltation was complicated. The 10 m isobath was bounded by the Dihe River, showing the state of westward siltation and eastward erosion. River sediment is the important material basis for the evolution of coastline and subaqueous slope. Waves and tidal currents are the main driving forces. While causing a decrease in river sediment transport, artificial facilities have also led to a significant advance of the coastline and erosion of estuaries. The northeast Laizhou shoal is in a state of erosion and disintegration due to human influence, and will continue to be eroded in the future.