Analysis on the Development and Evolution of Tidal Flats and Reclamation of Land Resource along Shore of Shanghai City

There was about 62% land resource of Shanghai developed as a result of the deposi-tion of sediment from the Yangtze River in the past 2 000 years.Especially in the latest 50 years,some efficient methods included Inning-Siltation Promotion-Inning,had been adopted to block up the sediment and to create land.These reclamated land resource amounting to 1.01×105hm2 had the land area enlarged by 15.8% in Shanghai.Obviously,it was important that the reclamation of land could alleviate shortage of land resource for the development of Shanghai,and promote industrial and agricultural development and capital construction.Based on the data of the tidal flat elevation data obgained by GIS and the long term field survey of hydrology and sediment,it was found that the abundant sediment from the Yangtze River and its adjacent areas,the hydrologic regimes around the Yangtze River estuary were advantageous to create new land resource.Many projects,which included crop cultivation works,waterway closure works,siltation promotion project on low tidal flats,piling up sediment from shallow seabed to the inner region of the dam,damming under water,etc.,had been successfully adopted around the shore of Shanghai.Different methods should be used at the corresponding phase in order to take a great advantage of the sediment supplied by the Yangtze River for promoting siltation.For example,some Inning Projects such as crop cultivation works and river branch closure works were developed at the middle and high tidal flats,which could accelerate the siltation of tidal flats and the increment of land resource.However,the projects of damming works and piling up sediment from shallow seabed to the inner region of the dam were done at the low tidal flats,which resulted in the expansion of the land resources and exposure of shallow sea topography.It was proved over the past 50 years that situations between reclaimed areas of land and changes of the areas of wetland and tidal flats could keep sustainable development.