水沙调节后荆江典型河道横向调整过程的响应——Ⅱ.上、下荆江调整差异初探

Responses of channel migration to changes of flow and sediment regime in the Jingjiang reach of the middle Yangtze River:Ⅱ:Differences between upper and lower sections

三峡水库2003年6月蓄水运用后,下游河道水沙过程已发生大幅变化,对于岸滩抗冲性较弱的荆江河道来说,河道的横向调整过程势必受到影响。采用考虑岸滩崩塌的河势研究数值模型,针对三峡水利枢纽工程运行所引发的水沙变异过程,初步探讨了荆江典型河道横向调整及河势变化对水沙条件变化的响应。对于下荆江石首河段来说,来沙减少后,冲刷加剧,局部河岸坍塌及平面变形加剧,主要发生在受弯道水流顶冲的位置,但河势演变趋势及平面变形总体上基本一致,并未发生较大变化。对于上荆江沙市—新厂河段来说,来沙量减小后,河道平面变形幅度总体上减小,局部最大减幅可达50%左右。

The flow and sediment regimes downstream of Three Gorges Reservoir have undergone a significant change since the beginning of its impoundment in June 2003. Accordingly, the spatial variations in downstream channel mor- phology will be adjusted, in particular in the Jingjiang reach of the middle Yangtze River with eroded bank materials. In this study, the lateral migrations of channels in the Jingjiang reach in response to changes in flow and sediment re- gimes are investigated. The turbulent flow and sediment transport as well as the bank erosion process are simulated by two- and three dimensional numerical models. No significant changes can be found in the overall evolution of channel planform in the Shishou segment in the lower Jingjiang reach. However, localized bank collapses and plane deforma- tions are likely to intensify due to the reduction of sediment transport, especially on the apex of bend. For the Shashi- Xinchang segment in the upper Jingjiang reach, the overall evolution of channel planform is reduced compared to that before reservoir impoundment. Up to 50% reduction can be expected in some local segments.