The flow passing through constriction in an open channel is highly three-dimensional. The center flow close to the bed, however, can be analyzed by combining the two-dimensional potential flows and by using the boundary layer analysis already developed by the authors. Although this method is applied successfully in order to calculate bed shear stress along the center line of flow, the calculation is rather tedious, and it is neccessary to know the water stage at least along the center line. Furthermore, it is not possible to analyze the phenomena of flow in the whole domain of the flow. For the practical purposes, the characteristics of flow are investigated by the aid of laboratory experiments and the appreciable results can be obtained based on the hydrodynamic consideration.