复式分汊水槽分汊口水流运动特性

Experimental Research on the Flow Characteristics of Bifurcation of Compounding and Branching Channel

分汊型河道是一种广泛存在的河流平面形态。当河道宽广时,河道行洪断面极有可能形成复式断面形态。存在江心洲的河道在演变过程中,洲头分流段水流运动往往起到了极其重要的作用。江心洲分流作用叠加复式断面滩槽交互作用,将共同对分流分沙产生影响,最终影响到整个河道形态的演变。为探究江心洲洲头水流运动特性对复式分汊河道演变的影响,设计了复式分汊河道的水槽试验。试验结果表明,复式分汊河道中,江心洲前的单一复式段,垂线流速分布基本满足对数分布;分流段流速主要受分汊形态的影响;复式断面形态是分汊口主槽和滩地流速变化的主要影响因素;在复式分汊河道的整治防护中,要着重关注江心洲洲头以及两侧的冲刷和两汊流速差异导致的淤积与冲刷;当流量增大到某一特定值时,复式分汊河道的断面形态可简化为简单的矩形河道进行研究。

A branched river exists widely as an important river form.When the river channel is wide,the cross section of the river channel is likely to form a compound section.In the evolution of the whole river morphology with the central bar,the flow movement often plays an extremely important role in the diversion section of the head of central bar.The distributary action of central bar superimposed on the interaction of compound cross-section floodplains and main channel will jointly affect the distributary and sediment separation,and ultimately affect the evolution of the whole channel morphology.In order to explore the characteristics of the flow motion of the head of central bar on the evolution of the compound braided channel,an experiment of a straight compound braided channel eroded by clear water is designed in this paper.The test results show that,①the vertical velocity distribution basically meets the logarithmic distribution in the compound section in front of the central bar in the straight compound braided channel;②the flow velocity of the compound braided river is mainly affected by the braided morphology;③the shape of compound cross section is the main influencing factor of the flow velocity change in the main channel and floodland at the bifurcation;④in the realignment and protection of compound braided channel,we should pay more attention to the scouring at the head of the central bar and both sides and the siltation and scouring caused by the difference of flow velocity between the two branches;⑤When the discharge increases to a certain value,the section shape of compound braided channel can be simplified to a simple rectangular channel for research.