Study on the Flow-sediment Conditions and River-bed Erosion and Deposition of Chongqing Reach after the Impoundment of Three Gorges Reservoir

Abstract Chongqing city is the important node of golden waterway of Yangtze River. As the promotion of the Yangtze River economic belt strategy and normal operation of Three Gorges Reservoir (TGR), more and more attention has been paid to the sediment problem of Chongqing reach. After the experimental storage of 175m in the TGR, Chongqing reach is located in the fluctuating backwater area, with export boundary conditions and river-bed erosion and deposition changed. In recent years, with the water storage of cascade reservoirs in the lower reaches of Jinsha River, the condition of water inflow and sediment in this section has changed and the river-bed is adjusted accordingly. According to prototype observation data from 2003 to 2017, the flow-sediment conditions and river-bed erosion and deposition of Chongqing reach after the impoundment of TGR at different stages were comarred and analyzed. Results showed that during the initial storage period of TGR, from June 2003 to May 2008, sediment erosion and sediment was mainly related to water and sediment of upstream, with whole reach in a state of erosion and intensity was about 140.8 million m3 every year. After the impoundment of TGR, from September 2008 to October 2012, the condition of incoming water and sediment in Chongqing reach maintained original change trend and sediment erosion was mainly related to impoundment of TGR, with whole reach in a state of erosion, but intensity was small. From October 2012 to December 2017, sand from upstream of Chongqing reach reduced greatly, so river bed was drastically adjusted and scour intensity increased significantly, was about 312.2 million m3 every year. It concluded that decrease of upstream sediment is one of the important reasons for increased scour intensity in Chongqing reach.