Study Of Topography Evolution Process In Nanhuizui Tideland And Adjacent Seabed

With the rapid development of economy and society in Shanghai, the problem of land resource short is outstanding day by day. Tideland reclamation works is the key to solve this problem from now on. Nanhuizui tideland is a transitional zone situated in a special area between the Yangtze estuary and Hangzhou Bay. It is the subcritical flow area of flood diffluence and ebb confluence between Yangtze Estuary and north shore of Hangzhou Bay. The flood current carried a great deal sediment to the tideland, the sediment deposit in this subcritical flow area. It makes the tideland silt quickly. It is the quickest speed of progradation in Shanghai tideland, and it is the biggest land resource reserve in Shanghai. In recent years, to alleviate the land resource scarce problem, large-scale reclamation engineering project has been carried on near Nanhuizui tideland. Thus it changed the water dynamic and sediment condition obviously. It will result in a new asjustment process of topography evolution. Consequently, it is important to study thetopography evolution process and feedback influence of reclamation engineering in Nanhuizui tideland and adjacent seabed. Based on the latest hydrological and sediment survey datum and the history sea charts, from the points of view on hydrodynamic condition, suspended sediment, sedimentary character, scouring and silting of the seabed, the evolution law of the Nanhuizui tideland and adjacent seabed is analyzed. Numerical Simulation was set up to study the hydrodynamic changes in Nanhuizui sea area. At last, it is discussed that main factors of topography evolution in Nanhuizui tideland and adjacent seabed.The results shows that 1993-1998 is the period of coastal progradation; 1998-2003 is the period of coastal adjustment; After reclamation project (2003-2005), there is a tendency of resuming progradation. According to Numeric Simulation of hydrodynamic condition and topography changes at Nanhuizui sea area, it is found that there is no obvious changes of the position of flood diffluence and ebb confluence, but a little affection to flood current field is limited to Nanhuizui water area with coast line out-shift. It caused increaser of the flood and ebb current speed in the north Hangzhou Bay, while it decreased in the outer of the South Channel. There is no influence to residual current, but biggish affect to sediment and water exchange. After the reclamation project, the tidal velocity in the north ofHangzhou bay strengthen and seabed is stronger scoured, while the tidal velocity in the east of nanhui shore weaken and seabed is silted. Supported by GIS, sea charts before and after projects were analyzed. It's found that the development of tideland experienced 3 periods in the recent 40 years. The year of 1960-1989 is the period of coastal progradation; 1989-1997 is the period of coastal adjustment; the year from 1997 to 2004, there is a tendency of souring. It is caused by the effect of the change of ocean dynamics, sediment flux to the sea and the constructions of some great coastal engineering projects.