| The Yangtze River is the world’s third largest and China’s largest river according to the annual runoff. It transports abundant water and sediment to the Yangtze Estuary and the East China Sea. For the estuarine areas, changes in suspended sediment have influence on the deposition and erosion of the riverbed, development of the delta and underwater sandbar, thereby affect the ecological environment of the whole estuary.With the changing climate, and the enhanced human activities, in particular with increasing mainstream dams being constructed, the sediment transported to the estuary and the sea is decreasing. It is possible to break the original estuarine sediment balance, cause beach erosion and variation of the sediment exchange. In order to explore the changes of suspended sediment in the Yangtze estuary area under the new situation, the paper employed the remote sensed image data from Operational Land Imager (OLI),TM (Thematic Mapper) and ETM+(Enhanced Thematic Mapper Plus) launched at Landsat satellites, and combined the surface sediment concentration (SSC) with vertical suspended sediment distribution formula to calculate the total suspended sediment quantity (TSSQ) in specific tidal stencils based on 30mx30m pixel grid.The SSC were obtained through the appropriate inversion algorithm. The water depth and flow velocity data of the corresponding satellite images were obtained by using the ECOM-si hydrodynamic model; 1367 suspended sediment profiles and relative velocity and water depth data were retrieved from there cruises of water and sediment survey, and were used to produce the formula of vertical distribution of suspended sediment and the key factors αω affecting the shape of the suspended sediment profiles based on the improved sediment diffusion formula. And the relationship between αω and SSC, flow velocity and water depth under each tide type was established; The water depth data and flow velocity data were resampled to the resolution of the same size of remote sensing images of 30 mx 30 m. The SSC data is integrated in the actual water depth according to the vertical distribution formula, and the total suspended sediment quality in the water column is obtained with the grid unit as the bottom area. Add up all the values of the grid, and get the total suspended sediment quantity in the whole study area (TTSSQ).According to the tidal conditions of Wusong tide station, the TTSSQ in different tide conditions were calculated. The total mass of suspended sediment in the spring tide and neap tide in July 2013 flood and January 2014 dry season were 5.976×107tons,2.793×107tons, 4.446×107 tons and 2.529×107 tons, respectively.In contrast, the TTSSQ in spring and neap tide in July 2013 and January 2014 were calculated with the vertical average method. The values were 3.432×107 tons,1.219×107 tons, 0.191× 107 tons and 1.210 ×107 tons. The values were relatively small compared with the results from the diffusion formula based method. The validation result showed that all the calculation results are credible except the result of neap tide in July 2013.For the first time, the method calculating the total amount of suspended sediment in the Yangtze Estuary is proposed, which makes up for the lack of the data, which provides the basic data support for other quantitative sediment research. |
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