Study On The Evolution Of The Coastal Belt Pattern Along The Southern Coast Of Hangzhou Bay

The coastal zone is located at the boundary of land and sea,which is affected by human activities and nature.It has a complex ecological environment and rich natural resources,and has become a treasure land for human gathering and social development.Hangzhou Bay,with its advantageous geographical conditions,large population and rapid economic development,is one of the most important regions in the country’s strategic development.In this paper,the evolution of the coastal zone pattern along the southern coast of Hangzhou Bay Province is studied,and the degree of shoreline change and the dynamic changes of coastal wetland utilization types within the coastal zone are studied,and the natural and man-made factors affecting the coastal zone are explored,it is conducive to grasping the current development and utilization situation in Hangzhou Bay.As a new technology,remote sensing technology plays an increasingly important role in landscape pattern extraction,dynamic analysis of ecological features and quantitative inversion at the macro level.By using remote sensing satellite Landsat-5TM and Landsat-8 OLI images as well as data sources of historical reclamation map of Hangzhou Bay tideland,based on GIS technology,Extracted coastline information from eight historical periods: 1500,1750,1800,1860,1950,1960,1970 and 1980,Coastline information was extracted from eight periods in 1985,1990,1998,2001,2005,2013,2017 and 2020 based on remote sensing technology.According to the length of coastline and the type of coastline,the spatial change results of coastline evolution were analyzed by digital coastline analysis System(DSAS).The conclusion is as follows: from 1500 to2020,the length of shoreline maintains an overall increasing trend.During 520 years,it expands to the sea continuously,increasing by 37.71 m in total,with an average growth rate of 72.52m/a,and an average annual growth rate of 0.11%.In the recent 8 periods of coastline type data,the proportion of natural shoreline has been decreasing,while that of artificial shoreline has been increasing.DSAS analysis showed that the whole coastal zone of Hangzhou Bay was silted to the sea,and the rate of coastline silting to the sea gradually increased.The maximum silting rate reached 479.89m/a,and a few endpoints were eroded in some years,with the maximum erosion rate of 14.42m/a.Remote sensing technology was used to extract the coastal landscape pattern distribution in 1990,2001,2013 and 2020 in the past 30 years,and analyze the spatial distribution characteristics and evolution of coastal landscape.The following conclusions are drawn: In the nine types of artificial vegetation,reservoir,marsh,beach,building,aquaculture area,river,road and sea area,although the proportion of artificial planting has been declining,but its proportion has been the largest,indicating that the study area has been mainly agriculture.And the area of the pond and the building is also growing with the development of economy and the needs of people’s life and production.The annual reclamation rate in the study area generally showed an upward trend,with the average annual reclamation rate only 0.70km2/a from 1500 to 1800,and 1.58km2/a from 1800 to 1980.After 1980,with the rapid development of China’s economy reform and opening up,the demand for reclaimed land was further increased.In particular,from 2013 to 2020,the annual reclamation rate reached the maximum of 18.55km2/a.These reclaimed areas are mainly converted to artificial structures.An analysis of the factors affecting the evolution of the Hangzhou Bay Coastal Zone from both natural and man-made factors found that among the natural factors,the Yangtze River,the Qiantang River River and its surrounding rivers provide the material basis for the erosion and deposition of sediment on the south bank of the Hangzhou Bay River and the natural conditions for human reclamation activities,but natural factors have less influence on the evolution of the Hangzhou Bay coast.Human factors include the economic development of the study area,population growth and the construction of seawalls.The rapid economic development and the rapid growth of the population have further increased the demand for land use and the demand for buildings and water consumption by the local people,resulting in a rapid increase in the area of buildings and reservoirs in the types of ground features,it has also promoted the local people to carry out large-scale reclamation of the tidal flat and marsh in the coastal zone,and the large-scale transfer of the tidal flat and marsh to artificial wetlands and buildings such as kutang,and artificial vegetation,etc..At the same time,in order to prevent the intrusion of seawater,reduce the impact of storm surge disasters,and ensure the safety of people’s lives and property,local seawalls and reclamation dams have been built to reduce the erosion of the coast by external tides,the tidal flat was pushed to the sea,which provided the conditions for the marsh vegetation to migrate to the sea,and made the Hangzhou Bay coastal zone expand to the sea gradually.