三峡水库蓄水后长江中游分汊河道演变机理及趋势

Branching Channels in the Middle Yangtze River,China

长江中游宜昌-湖口河段分汊河型分布广泛,涵盖了顺直分汊、微弯分汊及鹅头型分汊3种类型.本文依据三峡水库蓄水以来大量原型观测资料,总结归纳了长江中游各分汊河段的演变特征及其内在机理,并初步预测了其发展趋势.研究结果表明,三峡水库蓄水后,沙量大幅减少,同时局部河床边界条件发生变化,长江中游分汊河段普遍出现支汊冲刷发展、中低滩冲刷变形、高滩滩缘崩退等演变现象.伴随着三峡水库调度方式的不断优化,加之河床冲刷下造床质输移水平的沿程恢复,以及大量航道整治工程的作用,城陵矶以下分汊河段稳定性将优于荆江河段.

The middle Yangtze River from Yichang to Hukou is widely distributed with braided channels, including straight-braided channel, slight bending-braided channel and Goose-head pattern braided channel.Based on plenty of field data, the evolution characteristics and trend of the branching channels were studied. Since the water-impoundment of Three Gorges Reservoir, some new changes appeared in the braided channels in the middle Yangtze River, such as the severe erosion of tributary branch and channel islands. These phenomena are caused by the changes of water-sediment and river boundary conditions. As the operation of Three Gorges Project will continuously optimize, riverbed scouring also makes the bed load transportation on- way recover, and a large number of regulation works of navigation channels would play their role, the stability of braided channels downstream from Chenglingji would be better than Jingjiang reach.