On a stepped channel, three distinct flow regimes, nappe, transition, and skimming, occur successively with increasing discharge. This work proposes a criterion of the transition flow occurrence: a critical slope of the channel exists between mild and steep slopes, and for mild slopes, air pocket disappearance and nappe parallel to channel slope are defined as the lower and upper limits of transition flow, whereas for steep slopes, the two phenomena oppositely represent the upper and lower limits. The analytical approaches based on the criterion demonstrate the critical slope of 30° and predict the lower and upper limits of transition flow. The experimental data verify the existence of the critical slope and its prediction accuracy, and indicate that the prediction of the lower and upper limits of transition flow works well for both mild (<30°) and steep (>30°) slopes. During stepped channel design, employing the critical slope can control the transition flow occurrence, therefore reducing the risks caused by structure vibration and excessive splashing.

在阶梯式通道上，随着流量的增加，三种不同的流态，推覆、过渡和撇取依次发生。本文提出了过渡流发生的判据：在缓坡和陡坡之间存在通道临界坡度，对于缓坡，气袋消失和平行于通道坡度的推覆被定义为过渡流的下限和上限，而对于陡坡，这两种现象相反地代表了上限和下限。基于该准则的分析方法证明了30°的临界斜率并预测了过渡流的下限和上限。实验数据验证了临界斜率的存在及其预测的准确性，表明过渡流下限和上限的预测对于温和（< 30°）和陡峭（>30°）的斜坡。在阶梯式通道设计中，采用临界坡度可以控制过渡流的发生，从而降低结构振动和过度飞溅带来的风险。