The environmental assessment of the sediment after preliminary impounding of Three Gorges Reservoir

The reservoir sediment is one of the key factors which hindered the effective implementation of the comprehensive benefits of the Three Gorges Project. The preliminary impounding was carried out in the June of 2003. The environmental effect caused by the impounding is a social focus. The primary objective of this paper is to analysis the sediment of the Three Gorges Reservoir based on the observation. After preliminary impounding the water level of the reservoir has been raised and the flow velocity has been reduced. The character of the hydrology and sediment of the river within the reservoir has also been changed. Then the changes have great influence on the sediment deposition and erosion, riverbed geometry, flow velocity and flow condition. In order to solve problems mentioned above, the sediment prototype observation in the reservoir was performed and the results were analyzed intensively. There are a total of 45 observation stations were employed to work in this research in the upstream and downstream of the reservoir. Firstly, the hydrological character before and after impounding was observed respectively. Secondly, the sedimentation pattern of the reservoir and variable backwater area was analyses. Thirdly, the water surface slope roughness and silt was calculated and validated. Based on the observation and analyses, it is found that the effect of the sediment and change of the riverbed in the reservoir is little and can be controlled. The analysis method and research results can be helpful for the environmental assessment of other great project.