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Quantitative analysis on evolution of erosion and deposition in Nanhui tidal flat of Yangtze estuary

Nanhui tidal flat is a transitional zone situated in a special area between the Yangtze estuary and Hangzhou Bay. Supported by GIS, six topographic maps from 1953 to 2004 are digitalized. Meanwhile, the underwater digital elevation models between different periods are created and analyzed to investigate the topography evolution on Nanhuizui tidal flat. The results suggest: there was distinct erosion - accretion variation in this area in recent 46a; from 1983 to1990, the amount of eosion was 9.94 × 106 m3 (the erosion rate was 2.71 cm/a); while from 1990 to 1994, it turned to accretion (the accretion rate was 3.70 cm/a); from 1995 to 2000, the accretion rate increased to 6.45 cm/a. from 2000 to 2004, the accretion rate decreased to 4.57 cm/a, due to the anthropic activities and the adjustment of the tidal flat itself.