论沙市河段主泓南移的趋向性

Discussion on trend of thalweg moving to south in Shashi reach

沙市河段因主泓紧贴北岸荆江大堤,而成为长江中下游重点防洪河段。本文分析了该河段主泓变化的规律,发现主泓南移及其回复,与三八滩的冲淤消长相关;运用弯道环流理论、耗散结构理论研究了该河段演变及主泓位置变化机理:根据数模计算成果,三峡水库运行后水流的含沙量大幅度减少、坝下游冲刷使上荆江比降有所增大,预测沙市河段河势变化趋势,论述了主泓南移的必然性。同时因水库调蓄作用,流量变化幅度减小,河势趋稳定,将有利于防洪。

As the main flow in Shashi reach is near the north bank of Jingjiang Dike, the Shashi reach becomes an important reach of flood prevention. In this paper, the evolution law of thalweg in this reach is analyzed. It is found that the movement of thalweg to the south is related to the scour and deposition of Sanbazhou bar. Using the principle of bend circulation and the theory of dissipative structure, the evolution mechanism and thalweg movement of this reach are analyzed. According to the calculated result of mathematical model, with the operation of the Three Gorges Project the sediment concentration will greatly decrease, the slope of the Upper-Jingjiang will increase, and the thalweg will surely move to the south. At thesame time, the more uniform discharge processes will benefit to the stability of river pattern and flood control.