Hydraulic experiments and a numerical simulation were carried out for a Tidal Flow Generator (TFG). The TFG is an assembly of break waters with a small mouth for control of sea environment.
　The TFG makes uni-directional flow in front of its mouth by tidal motion. The residence time of an object is decreased by that flow. It means that the TFG can be used as a system for a water purification.
　By hydraulic experiments, some features of the flow came out from the TFG were measured. The velocity distribution of the flow is described as a 2D free jet flow's distribution. The intensity of central velocity in front of the mouth was well predicted by a proposed function.
　By a numerical simulation used an optimized discrete vortex method, the velocity distribution of the flow was well predicted also. The numerical method that we
proposed here had a high cost performance for the prediction of a local flow.