首次提出了上、下水垫深度的概念．以射流理论为基础推导了上、下水垫深度与双股入水水舌的水力要素之间的关系，指出了这两个水垫深度可用来划分拱坝水垫塘底板上最大动水压力区（“１＋１＝１”、“１＋１＞１”和“１＋１＜１”区）．结合小湾电站水垫塘的实验成果，给出了可用来迅速求解上、下水垫深度的图表．分析结果表明，当小湾电站水垫塘内水深为３７．８７ｍ时，中孔水舌入水的较优间距为１３．３～４０．５ｍ，与实验所得的１３～１７．５ｍ至４０～４９ｍ的间距基本相符 For the first time raised the concept of the depth of the water mats. Based on the jet theory, the relationship between the upper and lower plunging depths and the hydraulic elements of the double-inlet plunge is deduced. It is pointed out that the depths of the two plugs can be used to divide the maximum hydrodynamic pressure zone on the floor of the plunge pool “1 + 1 = 1”, “1 + 1> 1” and “1 + 1 <1” regions). Combined with the experimental results of the water cushion pond at Xiaowan Hydropower Station, a graph is provided for quickly solving the depth of the upper and lower water mats. The results show that when the depth of water in the plunge pool of Xiaowan Hydropower Station is 37.87m, the optimal spacing of water inlet into the water hole of the mesopore is 13.3 ~ 40.5m, which is in good agreement with the experimental data of 13 ~ 17.5m ~ 40 ~ 49m The spacing is basically the same