Abstract

Fuling reach is located in the confluence of Yangtze River and Wujiang River. According to the original operation scheme of the Three Georges reservoir, the water lever at dam would be maintained at 135m in the early stage. However, the impounding plan was adjusted after June 2003. In the flood season the reservoir will be preserved at 135m and raised to 139m after the main flood season. Under this impounding program Fuling reach lies in the 135m backwater region. The backwater zone and its degradation and deposition properties are greatly affected by the combination of inflows of these two rivers. Based on field datum collected in 2005, the erosion and sedimentation characteristics of the backwater reach with the effect of 135-139 impounding plan were investigated in this study. Results reveal that when the water level drew down from 139m to 135m the backwater reach was mainly characterized by erosion. At the end of the flood season the dam impounded from 135m to 139m and was also mainly dominated by erosion when the discharge was relatively large. During the dry season as the inflow reduced the reach was characterized by deposition. Degradation and deposition were alternately occurred in the confluent region due to the variation both of the inflow and sediment conditions of these two rivers. Lidu reach, lying in the tail of the backwater of the 139m scheme, is noted for its prominent erosion and sedimentation extent.

Keywords: the Three Gorges Reservoir; Fuling reach; erosion and deposition characteristics