长江中下游分汊河道的演变特点及稳定性

Characteristics of fluvial processes and stability of the braided channel in the middle and lower reaches of the Yangtze River

长江中下游是典型的河槽分汊型河流,主槽与支汊交替转化是最突出的演变特点。两者保持相对稳定是由于分流分沙对支汊有利;其发生转化是由于河势变化引起了主流线的摆动、汊道分流区水面横比降的变化及汊道的水、沙重新分配。经与国内外一些分汊河流对比,分析各种影响因素,指出长江属于江心洲高度发育、稳定性高的分汊河流。

The middle and lower reaches of the Yangtze River are classified as typical braided rivers with bifurcating channels characterized by the interchanging of position between the main and branch channels. The favourable conditions of diverting more clear water and less sediment to the branch make it possible to maintain relative stability for a rather long period. Mutual alternation occurs due to the change-of-flow feature in upstream which causes the change in transverse gradient at the point of diversion and consequently the redistrbution of flow and sediment into the branch. A comparison with some known braided rivers both in China and abroad indicates, after analysing all affecting factors, that the Yangtze River belongs to a bifurcating reach with highly developed islands and with high stability.