冲积性弯曲河道造床过程及演变机制

Process and Evolution Mechanism of Bed Formation in Curved Alluvial Channels

冲积性弯曲河道独特的几何边界特征,使得弯曲河道的水沙运动特性和河床演变特性与其他类型河道显著不同。为模拟自然条件下的冲积性弯曲河道河床冲淤演变特性,采用自然模型法的理念在试验水槽中塑造出近似的弯曲河道,探究不同水沙条件对弯曲河道形成和发育过程的影响。试验表明:进口水沙循环周期长、来水来沙强度较小时,弯曲河道达到动态平衡状态所需的时间相对较短,河道形成稳定河宽也较小。弯曲河道在形成和发育过程中,河道的形态要素主要由水沙作用条件决定,在一定变化范围内,当水沙作用循环变换周期较短、来流流量较小、含沙量较大时,有利于形成弯曲度较大的河道;而当来流量较大、水位漫滩冲刷浅滩时,所塑造的弯曲河道会偏向于宽浅形断面形态。在河道弯曲程度和河道横断面形态的调整中,水沙作用变化对横断面形态塑造的作用相对较强。

The unique geometric boundary characteristics of alluvial bends result in distinct water and sediment transport behaviors and bed evolution dynamics compared to other channel types.To simulate the natural evolution of riverbed scour and siltation in alluvial bends,we employed a natural modeling approach to replicate a representative bend channel in a laboratory flume to investigate the influence of varying water and sediment conditions on the formation and development of bends.The experiments reveal the following:1)A longer cycle of incoming sediment with lower intensity results in a quicker attainment of dynamic equilibrium in the curved river channel,with a narrower stable channel width.2)Throughout the formation and development of the bend,morphological changes in the channel are primarily dominated by the prevailing water and sediment conditions.3)Specifically,within a certain range of variation,shorter cycles of sediment transport,reduced incoming flow rate,and higher sediment concentrations facilitate the development of a more pronounced curvature in the channel.4)Conversely,higher flow rates causing scouring of shallow areas tend to shape the bend into a wider and shallower cross-section.The adjustments in channel curvature and cross-sectional morphology are predominantly driven by changes in water and sediment transport dynamics,highlighting their significant role in shaping channel morphology.