黄河高含沙洪水“揭河底”冲刷机理研究

Study on Mechanism of“River Bottom Tearing”of Hyper⁃Concentrated Floods in the Yellow River

“揭河底”发生时会导致河床形态在短时间内剧烈调整,影响河防工程安全。为研究“揭河底”冲刷机理、防治高含沙河流洪水泥沙灾害,以黄河中游小北干流河段为研究对象,分析了“揭河底”冲刷的基本条件,提出淤积物形态、水沙条件及前期河槽边界特征是主要影响因素;剖析了“揭河底”冲刷的物理机制,考虑河底淤积物在水流脉动力和冲击力作用下的转动揭起方式,通过力学分析建立了力矩平衡方程,推导得到“揭河底”的判别指标θ,用来反映淤积物自重力矩和水流揭掀力矩的比值以及淤积物自身厚度的影响;小北干流龙门站多年实测水沙资料显示判别指标θ存在临界值,当θ≤0.15时,“揭河底”会发生。

The formation of“river bottom tearing”will lead to the drastic adjustment of the river bed shape in a short time,thus affecting the safety of river defense works.In order to study the formation mechanism of“river bottom tearing”and provide technical reference for the pre⁃vention and control of flood and sediment disasters in hyperconcentrated rivers,the basic conditions of formation of“river bottom tearing”were analyzed by taking the Xiaobei main stream of the Middle Yellow River as the research object.It was found that formation of deposited sediments,water and sediment conditions and the characteristics of channel boundary were the main influencing factors.This study further analyzed motion mechanism of“river bottom tearing”and considered the rotational lifting of deposited sediments under fluctuating force and impact force.According to force analysis the moment balance equation was established,with which the critical discriminant indexθwas de⁃termined.θwas used to reflect the relative magnitude of gravity moment dividing lifting moment and the influence of thickness of deposited sediments.Whenθ≤0.15,the“river bottom tearing”would occur and the results were accurate after verification of years of measured data.