The impoundment of the Three Gorges reservoir and the release of clear water will cause different degrees of erosion in downstream of reservoir, and result in changes of river-lake relation and the characteristics of flow and sediment.According to observed data of Jianli hydrologic station,the changes of flow and sediment condition before and after impoundment of the Three Gorges reservoir were analyzed in this paper.The results show that the mean annual discharge at Jianli hydrological station is reduced.The flow is increased in dry seasons,and reduced in flood seasons after the impoundment of the Three Gorges reservoir.In the main flood season from June to September, the average flow of Jianli station is reduced to 6%-15% after the construction of the Three Gorges reservoir, and the decrease ratio of the flow in October and November is respectively 12% and 15%.The amplification range of the average flow in dry seasons from January to April is 6%~13.3%,and the flow variation of Jianli station is decreased within the year.The water level is lowered under the same flow conditions. The sediment concentration of Jianli station is reduced significantly, and the decrease ratio is up to 74.6% .The particle size of the suspended load and bed load increases, and the river bed is coarsening.%随着三峡水库的蓄水运用,清水下泄使坝下游河床受到不同程度的冲刷,江湖关系发生改变,引起水沙特性的改变.对收集到的三峡蓄水前后监利站实测水沙资料进行分析,结果表明:三峡蓄水运用后监利站年平均流量减小,年内汛期流量削减,枯季流量增大,其中主汛期6～9月份平均流量建库后较建库前减少了6％～15％,主汛后10月份和11月份流量减小幅度分别为12％与15％,枯水期1～4月流量平均增幅6％～13.3％,年内流量变幅减小,同流量条件下水位降低.蓄水后监利河段含沙量显著减少,减少率最多达到74.6％.悬沙中值粒径和床沙中值粒径均增大,河床呈粗化趋势.
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