中文摘要：

枢纽修建后引起水沙条件的变化必然造成年内交替型分汊河段河床的冲淤调整。通过实测资料分析的方法,分析了三峡下游近坝段典型年内交替型分汊河段的冲淤变化,并在此基础上总结了年内交替型分汊河段演变的一般规律。研究结果表明,近坝段年内交替型分汊河段年际间冲淤交替,整体以冲为主,水流动力轴线的摆动在分汊河段的冲淤调整中起到了关键作用,水库下泄的不饱和水流使得两汊交替冲刷,两汊发展的不平衡,洪水主汊冲刷幅度要大于枯水主汊,两汊高程差的逐步减小将引起河段水流运动和分流比的变化,对分流格局的稳定有着巨大影响。

英文摘要：

After hydro-junctions are built, the changes in water and sediment conditions will lead to adjust- ments in annually alternate braided reaches, and exert influence on their river patterns. By methods of field data analysis, the paper not only analyzes degradation process in annually alternate braided reaches in the near-dam reach, but also expounds the influence of dynamic axis of flow to river evolution. The results show that largely horizontal oscillation of dynamic axis of flow is the major factor affecting degradation adjustment process in annually alternate braided reach in the near-dam reach. The main channels both in the flood period and in the low water period are in erosion, but the erosion range in the main channel in the flood period is greater than that in the low water period. The decrease of elevation difference between the channels adjusts the discharge ratio of different channels.