Tidal flat evolution law and its mechanism on the south bank of Hangzhou Bay from 1959 to 2019

The tidal flat evolution law is an important basis for protecting and developing tidal flat resources. The complex flow-sediment conditions and high intensity of human activities in Hangzhou Bay have led to complex tidal flat evolution mechanisms. The tidal flat evolution law and its mechanism on the south bank of Hangzhou Bay under the influence of flow-sediment variation and human activities in the past 60 years were analyzed based on the hydrographic and bathymetrical monitoring data of Hangzhou Bay in the period of 1959-2019, combined with the process of deposit-promoting and reclamation. The results show that the tidal flat on the south bank of Hangzhou Bay has been deposited since 1959, with a deposition rate of approximately 6.70 cm/a during 1959-2003, and increased to 12.59 cm/a during 2003-2019. Large-scale reclamation projects and the increased tidal range are the main reasons for the increase in the slope gradient of the tidal flat profile. The periodic evolution of the plane morphology of the Andong tidal flat is related to the cycle of high and low runoff, showing the increased/decreased curvature in wet/dry years. The reduction of incoming sediment from the Yangtze River has not significantly affected the deposition of the tidal flat on the south bank of Hangzhou Bay. The reclamation project is the main reason for the increased deposition rate and decreased tidal flat width of the south bank of Hangzhou Bay.