高坝下游挑跌水流在水垫塘内的流态是相当复杂的。定性上可看作为淹没冲击射流和淹没水跃流的混合流态。一方面射流入水后沿程不断扩散，在冲击区对水垫塘底部产生巨大的冲击压力，具有淹没冲击射流的特征；另一方面在冲击区下游，高速主流贴近床底并沿程扩散和迅速跃起，同时在主流区的顶部形成较大的表面漩滚区，流态特征类似于淹没水跃流。针对这种混合流态，提出一个综合评价水垫塘消能效率的新指标，以便为水垫塘设计提供科学依据 The flow pattern in the plunge pool downstream of the dam is quite complex. Qualitatively, it can be regarded as a mixed flow state that submerges the impinging jets and submerges the jets. On the one hand, the jets continue to spread along the course of jetting into the water, creating a huge impact pressure on the bottom of the plunge pool in the impact zone, which has the characteristics of submerging impinging jets. On the other hand, in the downstream of the impingement zone, Rapidly leaping at the same time forming a large surface swirling zone at the top of the mainstream area, the flow characteristics are similar to submerged water jets. Aiming at this mixed flow regime, a new index for comprehensively evaluating the energy dissipation efficiency of plunge pool is proposed to provide a scientific basis for plunge pool design