Research on water-sediment variation and deposition-erosion in middle and lower Yangtze River

Based on the field hydrological data including Yangtze River main stream and tributaries,and the measured topographic data of the middle Yangtze River,Dongting Lake and Poyang Lake,the characteristics of water and sediment transporting,the patterns and variation of sediment erosion and deposition in the middle Yangtze River before and after the Three Gorges Reservoir operation are studied. The analysis leads to several conclusions,including:( 1) The annual runoff process is changed,such as the discharge of flood peak is cut down,the duration of medium discharge prolongs and the recession time is shorten. Not only sediment discharge in the middle Yangtze River reduces sharply,but also the source of sediment is undergoing a change.The water and sediment discharge diverted from Jingjiang reach to Dongting Lake continues to fall;( 2) The regime of the middle Yangtze River is steady in general,but the longitudinal erosion intensity of river bed increases obviously,both of the erosion intensity and rate are greater than the predicted values;( 3) The three flood diversion channels that connect the Jingjiang reach and Dongting Lake were in deposition before the operation of TGP,but they began to be scoured after 2003;( 4) The annual sediment siltation of Dongting Lake decreases greatly while Poyang Lake changes from siltation to scouring;( 5) The overall patterns of sediment erosion and deposition in the middle Yangtze River and two connected lakes were adjusted from siltation to scouring in general.