Analysis of erosion-deposition characteristics in the tail area of Three Gorges Reservoir under altered water-sediment conditions

Abstract

With the commissioning of cascade reservoirs in the lower reaches of the Jinsha River, sediment discharge at Xiangjiaba Station has decreased substantially, leading to corresponding sediment reduction in inflows to the Three Gorges Reservoir(TGR). To investigate the changes in erosion-deposition characteristics in the tail area of TGR under altered water-sediment conditions, hydrological data from main control stations on the Upper Yangtze mainstream, Minjiang and Jialing Rivers was analyzed, along with years of cross-section data from Tongluoxia to Fuling in the TGR tail reach. Comparative analysis of changes in inflow water-sediment into the TGR and siltation changes in the tail area of TGR before and after 2012.The result show that compared to the period from 2003 to 2012, there was no significant change in the runoff at Cuntan station during the period from 2013 to 2024, while the sediment discharge decreased by about 63%. The intra-annual distribution was more concentrated from July to September. The sediment deposition in the river section from Tongluoxia to Fuling decreased by about 56%. The contribution rate of sediment deposition increased during July to August and decreased in November. The result indicate that the decreased sediment inflow into the TGR has significantly alleviated sedimentation in the reservoir tail section. With sediment transport becoming more concentrated during flood seasons, the proportion of July—August deposition contribution to annual sedimentation rose.During flood periods with high sediment-concentration inflows, appropriately reducing peak-flow clipping could further mitigate tail-section sedimentation, provided operational conditions permit.

Keywords

tail area of Three Gorges Reservoir / water-sediment regime change / reservoir sedimentation