Sediment Transport Mechanism In Yangshan And Its Surrounding Waters

Because of its unique location and natural geographical conditions,Yangshan sea area was included in the planning and construction of key port projects after discussion by the state at the end of the 20th century,which has produced huge economic and social benefits.In addition,with the construction of port engineering,the hydrodynamic environment in the sea area has changed,which has affected the sediment transport and sediment law to some extent.The research and analysis of this phenomenon provides a theoretical basis for project planning and design,provides some valuable reference materials for port waterway construction,and helps to minimize the negative impact of marine-related activities and protect the marine environment.Thus,Based on the finite volume ocean numerical model(FVCOM)and its sediment module(FVCOM-SEDIMENT),this paper studies the hydrodynamic environment change and sediment distribution and transport mechanism in Yangshan sea area under the combined action of runoff carrying and background suspended sediment.The high-resolution(50 m×50 m)three-dimensional numerical model of hydrodynamic sediment with Dayangshan as the center,including the Changjiang Estuary,Hangzhou Bay and its adjacent waters,is established.After the feasibility of the model results is verified by the measured data,the temporal and spatial characteristics of hydrodynamic environment,sediment distribution and transport mechanism in Yangshan and its adjacent waters are systematically analyzed,which has strong practical significance.Research shows that:(1)From the tidal current characteristics of Yangshan and its surrounding waters,the tidal discriminant coefficient and tidal current discriminant coefficient of Yangshan sea area are 0.416 and 0.252,respectively,both of which are less than 0.5,so it can be judged that the sea area is a normal semidiurnal tidal pattern and a normal semidiurnal tidal flow pattern;In addition,through calculation,it can be known that the possible maximum water surface velocity in Yangshan sea area is 2.5 m/s in the deep-water channel area between the big and small Yangshan mountains,and it gradually decreases to both banks.(2)From the spatial and temporal distribution characteristics of hydrodynamic environment in Yangshan and its surrounding waters,the distribution of velocity and energy density is relatively consistent,and the larger area is located in two promontories in the north of Dayang Mountain,among which the velocity and energy are the largest in the area near the deepwater channel in the north corner of the ocean.The maximum velocity of flow field in Yangshan sea area can reach 1.6 m/s at high tide,s-e at high tide,1.2 m/s at low tide and N-W at low tide.The average velocity of tidal current in this sea area generally exceeds 0.4 m/s,and the maximum average velocity can reach above 0.9 m/s,and the maximum velocity can exceed 0.8 m/s and 2.2 m/s;The average tidal current energy density in this sea area exceeds 0.1 kW/m,and the maximum average tidal current energy density can reach more than 0.7 kW/m2,the maximum tidal current energy density generally exceeds 1.0 kW/m2,and the maximum tidal current energy density can reach more than 6 kW/m2.(3)From the sediment distribution and transport mechanism in Yangshan and its surrounding waters,and the concentration distribution and seasonal characteristics of planktonic sediments in high waves,the sediment combination in the muddy area of Yangshan sea area in this paper mainly comes from the sediment carried by Qiantang River runoff into the sea and the uplift and transport of sediment in Hangzhou Bay shoal;The settlement speed in the north and west of Yangshan sea area is higher than that in the south and east,Therefore,the floating sediments in the sea area show the spatial distribution characteristics of high in the west and high in the east.During tidal movement,the direction of sediment transport near Nanhuizui is west,and the direction of sediment transport near Hangzhou Bay is mainly east,which can pass through Yangshan sea area,so that there is a certain concentration and accumulation of suspended sediment on the west side of the sea area,which makes the suspended sediment in the sea area show the spatial distribution characteristics of high west and low east.