为了研究山区河流宽窄相间河段不同流量下水流结构特性，以雅安宝兴河上游河段为研究对象，概化实际河道，并建立三维水流计算模型。结果表明①小流量下，窄段上游无明显壅水现象，宽窄相间河道显现出与顺直河道相似的特性，随着流量的增加，窄段上游壅水剧烈，宽段到窄段沿程断面平均流速呈现“增加—相对稳定—骤减—相对稳定—增加”的分布规律;②受河宽、壅水和回流影响，不同流量工况下宽段横断面的水流特性分布较窄段更加复杂，且在宽段的壅水区与非壅水区流速分布规律差异亦较大;③不同流量状况下，宽段床面剪切力剧烈变化将造成卵石沿程运动的不连续性，宽段河床呈现周期性往复发展的复归性变形，从而维持了宽段河床结构的稳定，而在窄段，河道在较大的床面剪切力长期作用下，形成了与周围环境相适应的河床结构，以消耗窄段较大的水流能量，从而保护河床的稳定。

In order to study the flow characteristics in wide and narrow alternated channels under different discharges, we chose upstream reach of Baoxing river as research object and established a three-dimensional flow numerical model through simplifying the actual river. Results show that 1) under low discharge, backwater at upstream reach of narrow section was not obvious, and wide and narrow alternated channel showed characteristics similar to straight channel; 2) with the increase of discharge, backwater in the upstream reach of narrow section was intensive, and the distribution of cross-section average velocity showed a multi-stage regularity (stages of increasing, relatively stable, rapidly decreasing, relatively stable and finally increasing);3) affected by river width, backwater and reflux, cross-section flow characteristics in wide section was more complex than that in narrow section, and the velocity distribution at backwater area was obviously different from that at non-backwater area;4)under different discharges, dramatic changes of bed shear stress in wide section will lead to discontinuous movement of pebbles, and deformation of riverbed in wide section showed cyclical tendency, which is in favor of stability of the wide river bed structure; 5) while in the narrow section, riverbed structure was compatible with surrounding environment under long-term larger bed shear stress, then larger flow energy in narrow section can be expended and riverbed stability can be guaranteed.