Numerical Study Of Suspended Sediment Transport In The Offshore Near Changjiang Estuary

Basing on ECOMSED model, a 3-D hydrodynamic-transport numerical model for the offshore area near Changjiang Estuary in the East China Sea has been developed. The hydrodynamic module is driven by tide and wind as well as inflow and outflow currents. Effect of wind generated waves also includes in the current modeling framework. Sediment module includes sediment resuspension, transport and deposition of cohesive and non-cohesive sediment. Settling of cohesive sediment in the water column is modeled as a function of aggregation and deposition. The numerical results are compared with observation data which measured during Aug, 2006 in the East China Sea. To improve the accuracy of results,This paper adds a nudging assimilation method to ECOMSED model, establishing a assimilation model, and tides and suspended sediment concentration in the offshore near Changjiang Estuary is simulated by this model. A relaxation term is added to the continuity equation and sediment transport equation respectively to nudge the calculated value to the observation data. Numerical experiments show that the data assimilation in numerical model which can improve the accuracy of results. Apply this method to the simulation of the suspended sediment in the Offshore Near Changjiang Estuary, and modify the horizontal diffusivity of the suspended sediment transport, and the result improves on. The result of simulation can describe the hydrodynamics and the sediment transport in the Offshore near Changjiang Estuary.The distribution of suspended sediment concentration shows that the sediment concentration reduces gradually from the seashore to the offshore area, and divided into the east and the west two parts by 123°E, and the west is higher, and the east is lower. The front of suspended sediment concentration is 150km far from shore in the Subei coastal area. Suspended sediment concentration eastern of 123°E is less than 10 mg/L. The higher concentration of suspended sediment concentration generally appears at the esturay area, and exceeds 300 mg/L. The Changjiang Esturay and the Hangzhou Bay is highest, and the counter of suspended concentration parallels seacoast line in the Minzhe coastal area. The front of suspended sediment concentration is about 80km far from shore. The concentration divideds into the south and the north two parts by 30°N, and the north is higher than the south. As a whole, the suspended sediment is advected to the south-east mainly, and the continuous muddy water is distributed in the Subei coastal area, the Changjiang Esturay, the Hangzhou Bay and the Minzhe coastal area. The muddy water in the Subei coastal area and the Minzhe coastal area depends on the resuspension and seacoast current taking. The muddy water in the Changjiang Esturay depends on sediment which is taked by Changjiang diluted water.Numerical results of concentration time series in the observation stations show two peaks and two valleys, according with the observation data. It is mainly affected by tidal current. The suspended sediment concentration is related to the tidal current during a tidal cycle, and the maximum concentration appears 1~4h after the current maximum velocity.