Abstract
Based on FVCOM hydrodynamic numerical model and coastline topographic data in 2013, a three-dimensional numerical model of fine sediment transport in Hangzhou Bay has been established to explore the water and sediment exchange mechanism between Hangzhou Bay and the open sea at different typical sections. The results of validation with measured and satellite retrieved data show that the model can well simulate the process of water and sediment movement in Hangzhou Bay. Compared with the calculation results of the coastline topographic data of Hangzhou Bay in 1974 and 2020, the influence mechanism of shoreline change on the water and sediment exchange mechanism between Hangzhou Bay and the open sea has been studied. The results show that the sediment transport inside and outside the Hangzhou Bay is generally in the pattern of north-inflow and south-discharge. Compared with the coastline in 1974, the sediment transport from Yangshan port in the north of Hangzhou Bay and Zhoushan Islands in the middle of Hangzhou Bay increases when the coastline is pushed into the bay in 2020, while the outward sediment transport from Jintang Channel in the South decreases. The overall trend features that the sediment transport into the bay increases, with the bay mouth silting. In the three sections extending from Hangzhou Bay to the open sea, the inflowing water and sediment of the horizontal section on the north side is decreasing, while the discharged sediment from the south side and the inflowing water and discharged sediment from the vertical section at the east side are increasing.
Highlights
The results show that the variation trend and magnitude of SSC at each point are consistent with the remote sensing inversion value, so the suspended sediment model has high accuracy in the large area sea area of Hangzhou Bay
Based on the statistics of tidal fluxes and sediment transport during spring and neap tides, and the dominant tidal volume and dominant sediment representing the relative strength of the rising and falling tides, this paper analyzes the changes of hydrodynamic and sediment transport in typical cross-sections, and analyzes the influence of shoreline changes caused by tidal flat reclamation on the water and sediment exchange mechanism between Hangzhou Bay and the open sea
The change of net tidal flux of each section is counted to analyze the influence of shoreline change on the water exchange mechanism between Hangzhou Bay and the open sea, and a sketch map is drawn according to the relative position of each section (Figure 7, the positive value of ordinate indicates the transport to the bay, and the negative value indicates the outward transport to the bay)
Summary
Based on the unstructured grid finite volume method ocean numerical model FVCOM[14], the model is partially modified in combination with the sediment characteristics of Hangzhou Bay. The resuspension model is calculated by the formula proposed by Van Prooijen[15]. Considering the great influence of suspended sediment concentration on the vertical distribution of density in Hangzhou Bay, the formula proposed by Winterwerp[16] is used to calculate the water density, and the effect of suspended sediment concentration on water density is considered. The. Richardson number[17] of the turbulent closure equation is introduced into the calculation formula of the bottom friction coefficient, and the influence of suspended sediment concentration on the bottom boundary layer is considered. The settling velocity is calculated by using the settling velocity formula of suspended sediment flocculation proposed by Cao[18]. The diffusion equation of suspended sediment concentration in the model is as follows:.
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