Numerical Study of the Influence of Donghai Bridge on Sediment Transport in the Mouth of Hangzhou Bay

Donghai Bridge locates in the north mouth of Hangzhou Bay and south of Nanhui nearshore waters, where is the main channel for water and sediment exchange between Yangtze River Estuary and Hangzhou Bay. The construction of Donghai Bridge would influence the sediment transport in the mouth of Hangzhou Bay. In this paper, numerical simulations of the hydrodynamic environment and sediment transport process were carried out before and after the construction of Donghai Bridge by using ECOMSED model. Moreover, the satellite remote sensing images from MERIS and TM sensors were used to provide further proofs about the influences of the sediment transport caused by the construction of Donghai Bridge. The results show that a sediment belt, which is about 3.5 km wide, has developed in the west of the bridge axis at flooding time. However, it is only about 1 km and just located in the east of the bridge axis at ebbing time. The reason is that the velocity increases between the piers, and thus makes an intensification of sediment resuspension. Contrast to the increasing of the suspended sediment concentration (SSC) near the bridge axis, the SSC decreases about 5% in the area about 5 km away from the sediment belt. The results also show that a high SSC region with 8% increase appears between the northeast of Tanhu Island and the west of the bridge, and a low SSC region with 12% decrease appears just to the south of the high SSC region.