TEMPORAL-SPATIAL VARIATION OF CHENGTONG REACH AT YANGTZE ESTUARY AFTER CONSTRUCTION OF THREE GORGES DAM

River channel sedimentation in estuary of the Yangtze River can be affect by the construction of reservoirs in the upper river that reduces the amount of sediment discharge. To evaluate the dynamic changes of sedimentation and erosion of Chengtong reach at the Yangtze Estuary, the digital elevation model of underwater topography were designed and constructed on the basis of the measured bathymetric data in 2006 and 2012. The results indicated that although the runoff of lower reaches remained stable, the sediment discharge reduced significantly due to the existence of large number of reservoirs on the middle and upper reaches of the Yangtze River. Annual sediment discharge was reduced from 134 million tons in 2007 to 60 million tons in 2011 by the measured data of the monitoring station in Datong. The river channel of Chengtong reach was in the state of erosion during 2006 to 2012, the net erosion thickness was about 0.37m, and the net erosion volume was 18.9 million m(3). The water channels of Chengtong reach were changed because of the decreasing amount of sediment discharge from the upper river. Fuzhong and Fubei water channels was eroded and deposited respectively. The position of the deep channel in Liushahai channel was swung and the right side of the river channel was getting widen. The deep channel in the right side of Tongzhousha east channel near Tianshenggang was in the state of erosion and became deeper. The riverbed of Langshansha east channel shifted to the left side obviously.