Response Of The Strait-channel Effects To Habor Project In The Yangshan Sea Area

Yangshan sea area lies in the Qiqu Archipelago, the south of Changjiang Estuary, the west of East China Sea, the outside north of Hangzhou Bay, and on the south-east of Luchaogang of Nanhui. Its dynamical characteristics of water current and suspended sediment are very complex because of its unique trumpet-shape and topography of strait. Its characteristic of dynamic condition is decided by the contrast of the forces between river runoff and tide flow and wave. The transportation and deposition of sediments are mainly decided by the suspended sediment concentration from Changjiang Estuary and the strength of the flow. Silt transportation and sedimentary mechanism in the area are discussed from dynamics, which shows that rapid current, high suspended sediment concentration and little deposition are themain features of the area.Yangshan Harbor Area of Shanghai International Shipping Center constructed because of the well water-depth condition in June, 2002. The construction of a series of projects changed the natural strait-channel effects of Yangshan Sea Area, the water dynamics, the distribution of sediment and the evolvement of topography etc. The Pattern of ebb-tide dominant has been changed to the balance of ebb-tide and flood-tide, the Kezhushan strait-channel kept the ebb-tide dominant as the only no-blocking strait-channel. And the Yangshan Sea Area has been in the situation of weak deposition.The resource of sediment was controlled by the big environment of adjacent sea area, but the distribution of sediment has changed in some areas because of the changing of strait-channel topography. The isolines of suspended sediment concentration were uniformity in the main routeway after the blocking of strait-channels. The water dynamic decreased, the function of separation and convergence of tidal current disappeared and the coarser particles settled after the construction of project. The sediment changed from coarse to fine and was coarser in some areas, which reflected the strait-channel of Yangshan Sea Area.The evolvement of topography has changed along with the changing of tidal current and the sediment. The range of siltation aggrandized after the construction of project, and the erosion water area occurred in the forefront of dock and Kezhushan strait-channel. The changing of tidal current and topography of strait-channel, the leakage of filling silt and the region of mud casting brought out the big area of siltation. At the same time, the sediment was easy to settle when the time of before and after high tide and low tide because of the minimum water velocity and maximal suspended sediment concentration. Furthermore, the water depth of dredging affects the intension of siltation, which increased with the adding of water depth.Generally speaking, the topography of strait-channel of Yangshan Sea Area, the tidal current and distribution of sediment have changed after the construction of project, and the seabed has adjusted accordingly and the adjustment continued at all times.