岱山西北海域海床冲淤演变分析*

根据不同年份的水深地形资料及遥感影像，采用GIS技术对近30 a来岱山西北岸线变化及海床冲淤进行数字化分析。同时，结合该海域的水文泥沙特征及人类活动因素，研究海底冲淤变化的主要影响因素。综合分析表明：2011年以前岱山西北海岸岸线稳定，岸滩经历了由滩淤槽冲转为滩冲槽冲的动态演变过程，除岱山西部与大鱼山之间的槽沟局部地形变化较大外，其它海区冲淤速率不到10 cm/a，整个海域的侵蚀速率有加速趋势。2011年之后，岱山北部开始实施大规模围涂工程，岱山西北近岸5 m等深线以浅的岸滩发生1.75 m/a的淤积,而计算范围内的其它海区仍以微侵蚀为主。岱山西北海域泥沙主要以过境输移为主，长江来沙量的减少和近年围垦活动的增加是该海域海床冲淤演变的两个主要影响因素。

Seabed evolution off northwest Daishan island

Based on the topography,bathymetry data and remote sensing image in different periods,we adopt the GIS technology to analyze changes of Daishan northwest coastline and the seabed erosion and silting offshore.Then local hydrological and sediment features and the human sea reclamation activities are combined to study the main influential factors on the sea erosion and silting of the northwest area of Daishan island in recent 30 years.Research shows that,before 2011,northwest Daishan coastline was stable,and the seabed had experienced a dynamic evolution process from silting on beach and erosion in trough to erosion both on beach and in trough.The erosion and silting-up rate were generally less than 10 cm/a in the sea area between Daishan island and Dayushan island,with a trend of overall increasing erosion rate,except for some local troughs where the seabed change was more intense.After 2011,due to the large-scale reclamation project,seabed shallower than 5 meters off northwest Daishan silted with a rate of about 1.75 m/a,while other sea areas were still rushed by erosion.The sediment route in Daishan northwest mainly depends on the transit transport.The reduction of sediment from the Yangtze River and the increase of the reclamation activity in recent years are the two main influential factors of the seabed sediment evolution of the waters.