In case designing the counter-dam constructed to minimize the scouring of the downstream side of the main Sabo-dam, it is necessary to take into account the depth of scour by falling water. To calculate the depth of scour, the depth of the water cushion which varies with the influent hydraulic quantity between the main and counter-dam is needed. In this study, the characteristics of jet flow of water fall which is the cause for scour, and the depth of the water cushion between the main and counter-dam are examined. The flow in the water cushion is thought to be two dimentional jet flow, however the hypothesis that the flow is one dimentional may be available for the actual analysis of the phenomena Then, in this study, the equation of one dimentional mean velocity derived from the Albertson's two dimentional jet flow theory is applied for the analysis of the water depth. Secondly, applying the theory of momentum, the equationes for the calculation of each depth at the cross sections of scoured hole are introduced under the thought that the maxium height of hump, and the water depth and the height at top bed of the front of scoured hole are known. The experiment performed to ascertain the characteristics of flow in the scoured hole has showed good results and each depth of water cushion at their cross sections, calculated by the equations, has almost agreed with the results of the experiment.