Sedimentation at estuary of 66 tributaries in the Three Gorges Reservoir

Abstract

There are about 66 tributaries distributed in the Three Gorges Reservoir (TGR) area. As obvious deposition has been observed at estuary of most tributaries estuary since the water-impoundment of TGR, the possibility of sedimentation leading to form entrance bar at estuary of tributaries should be highly concerned. Based on data of topography and cross-sections, the DEM digital elevation model is established to calculate the aggradation volume at the estuary of tributaries in TGR, also the scouring and silting thickness at estuary will be demonstrated. Changes of cross-sections and thalweg caused by aggradation are also studied. The results show that: (1) The aggradation volume at estuary of 66 tributaries in TGR was 180 million m3 from March 2003 to November 2011; (2) hydrodynamic conditions at estuary of tributaries weakened after the operation of TGR, which is the root cause of sediment deposition. The extent of sediment silting was affected by sediment from the tributaries and backward water from the mainstream, meanwhile the dynamic state of river course at estuary had an important influence on the range of aggradation; (3) sediment deposited at the estuary mainly derived from backward water of mainstream, and less from the tributaries. As sediment concentrations both in mainstream and tributaries decreased obviously and will be continually maintain a low level, there is little risk for the formation of entrance bar of tributaries in TGR.