中文摘要：

基于长江上游水文局实测地形、水文、泥沙资料，针对二三峡大坝175m方案蓄水后对变动回水区产生壅水影响，借助SMS平面水流二维数学模型，对成库前后龙门浩河段水流特性变化进行了研究分析。研究结果表明，成库后非汛期内，该河段呈库区特性，尾水抬高，流速、水面比降、水流功率大幅下降，汛期河段恢复天然河道，水流特性与成库前一致。取各时期平均流量下的水流特性代表各时期水力因子的平均值，通过成库前后各时期相同流量下龙门浩河段水流特性模拟对比，发现蓄水维持期水力因子的变幅最大、蓄水期次之、消落期最小、汛期则不发生变化。通过加权估算，成库后年内平均水流功率较成库前下降47．9％，同时由于水流功率的年内变化分布极不均匀，将导致河段输沙规律发生变化。

英文摘要：

This article is based on the topography, hydrology and sediment data measured by the Upper Yangtze River Waterway Bureau after the impoundment of the Three Gorges Reservoir to 175 m height to study the change of the streamwise backwater effect with the aid of the SMS of a planar 2D mathematical model. The change of the Longmenghao reach flow before and after the impoundment is analyzed, and the analysis results show that： （ 1 ） after the impoundment in non-flood season, the river reach in the reservoir has the characteristics that the tail water is too high, flow velocity, water surface slope and water power have fallen sharply; and that in the flood season, the reach becomes natural just as that before the impoundment; （2） the average flow rate is taken to represent the average of the hydraulic factor condition; under the same flow before and after the impoundment, the Longmenhao reach flow simulation of different periods is compared, showing that the change amplitude of hydraulic factors in impoundment period is the largest, that in storage period is smaller, that in drawdown period is the smallest, and that in the flood season has no change; （3） weighted estimation shows that after the impoundment within the first year, the average stream power reduces by 47.9% compared with that before impoundment, and at the same time, the stream power yearly change distribution is extremely uneven, which will lead to big changes in sediment transport in the reach.