Study of Critical Values of Sediment Concentration for the Change from Deposition to Erosion in Yangtze Delta

摘要

The deposition rate of the delta decreased when seawards sediment decreased. The critical values of sediment concentration mean the concentration which kept balance of erosion and deposition. According to the topography data of Yangtze estuary between 1958 and 2007, the change process of the isobaths is established. Based on the datum line of east longitude 122°17', the empirical relation between the erosion/deposition rate of delta and the sediment amount was built and the critical values were calculated. The trend of the change of sediment concentration was also forecasted. The isobaths of -10 m, -15 m and -20 m have been eroded from 2000 to 2007 because of the decrease of the sediment discharge into the sea. The critical values of the isobaths of -10 m, -15 m, -20 m is 24.88, 24.23, 20.40 million tons per year and the numbers are decreasing in the deep sea.