冰期河流弯道冰水动力学行为研究

Behavior analysis of ice and water flow dynamics in a river bend during freezeup period

以黄河什四份子弯道为研究对象,基于2019-2020年度的凌情监测影像及现场试验数据,分析了河流弯道冰水动力学行为特征。结果表明:上宽下窄的河道形态是造成弯道卡冰的主要原因,流凌-封河阶段,弯顶节点工程对水流的顶托作用促进了上游回流区的形成;受弯道离心力作用,河冰聚集于河道凹岸一侧,并在回流区堆积形成冰桥,从而缩小了断面过冰面积,河道逐渐封冻;弯顶下游流速大且来冰量少,形成清沟,主流向河中发展;冰塞堆积于弯顶上游凹岸主河槽内,水流被挤压至凸岸非冰塞区,弯道主流易位;在稳封期,河道冰水动力特征基本不再变化,在解冻开河期,凸岸非冰塞区流速较大,主流区冰盖优先解冻且沿主流输移,回流区冰盖最后消融,河道主流逐渐恢复至畅流阶段,整体呈复归式。

Based on the monitored images and field experiment data of 2019-2020,the behavior characteristics of the ice and water flow dynamics of the Shisifenzi Bend in the Yellow River was analyzed.Results show that the main reason for the ice jam in the bend is the morphology of the river channel,which is wide at the upstream and narrow at the downstream.During the open flow to freezeup period,the project at the bend apex promoted the formation of upstream backflow area by supporting the water flow.Affected by the centrifugal force of the bend,the river ice accumulated on the concave bank of the river and formed an ice bridge,which reduced the ice area of the river,then the river gradually froze up.In the downstream of the bend apex,the flow velocity was larger and lack of adequate ice,so the open flow area formed and the mainstream developed towards the middle of the river.The ice jam accumulated in the main channel of the concave bank of the bend apex,so the flow was squeezed to the non-ice jam area of the convex bank,and the mainstream of the river channel changed its path.The hydrodynamic characteristics of the river ice basically did not change during the stable freezeup period.During the breakup period,the non-ice jam area on the convex bank had a high flow velocity and gave priority to thawing,then the ice transported along the mainstream line,the ice cover in the backflow area melted the last,and the mainstream of the river gradually returned to the free-flowing status,showing a regression trend.