Research On Erosion-deposition Dynamic Of Subaqueous Coastal Slope Along Zhenhai In South Hangzhou Bay

The research area,Zhenhai section of south coast of Hangzhou Bay,located between Ningbo and Zhoushan Islands,which embraces the west bank of Jintang Bridge.In order to obtain more detailed information of the development,the evolution process of erosion-deposition and the engineering-environment effect of muddy port coastlines,it is reasonable to implement research about the evolution as well as the changing features which contains the changes in the plane erosion-deposition of underwater slope and the adjustment of scour-and-fill shape in typical sections during the past years.Meanwhile,the sound operation,dredging depth and sustainable development of harbor district partially counts on the results of research.But beyond above,the marine engineering projects of surrounding waters and the Hangzhou Bay area parallel line G92N(Hangzhou Ningbo high-speed line),the first phase project of the Ningbo section all would acquire instructive as well as academic benefit from research.In addition,apart from enriching the contents of estuarine and coastal research,it is rewarding for the later sustainable development and utilization of resources in the other deep water shoreline.On the basic of researching on the gathered admiralty charts and bathymetric charts of various years,by utilizing the technology of Geographic Information System(GIS)to study the change of shoreline,,the distribution of representative isobaths,the changes of plane erosion-deposition shape of subaqueous coastal slope and adjustment of erosion-deposition shape of section of representation in Zhenhai harbor district,in accordance with hydrologic and sediment observation data,it is straightforward to research the dynamic tendency of sluicing silt shape of subaqueous coastal slope in the survey area.Consequently,in the surrounding waters of Zhenhai section of the south coast of Hangzhou Bay,it is available that tidal flat,five-meter isobaths and underwater shoals all show the trend of seaward movement.Meanwhile,offshoring amplitude of tidal flat is about 334 meters to 1912 meters with annual migration rate of 6.19 meters/annual to 35.41 meters/annual approximately,relatively the offshoring amplitude of five-meter isobaths is about 600 meters to 5700 meters with annual migration rate of 11.11 meters/annual to 105.56meters/annual closely during the past fifty-four years.Besides,it is showed that the surrounding water of research area is total siltation shape with siltation amplitude of 1.10 meters and annual siltation rate of 2.04 centimeters/annual nearly,which reveals that,under near natural conditions,the research area keeps balance between sluicing and siltation,whereas the reclamation and siltation promotion projects recently exert a positive influence on the increase of siltation rate.In addition,the Three Gorges Project partially decreases the sediment loads in the research area,which results in the decreased rate of siltation as well as sluicing in partial area.Furthermore,with the influence of water-flow retardation of cross-sea bridges,partial siltation exists in research area,and partial sluicing might appear around bridge pier.From all research above,tidal flat keeps the trend of seaward movement and the movement rate would decrease as the development of tidal flat,it is thought that the balance would be reached with the existing coastal line out of influence of external conditions.