In recreational beach, groins and offshore-breakwaters are often constructed to protect the shore from erosion by waves. But such structures are feared to obstruct smooth flowing of tidal currents and to stangnate polluted water near the shore, especially in summer when sea is calm.
　In this paper, taking the beach of which equi-depth lines are parallel each other, influence of groins and breakwaters on dispersion of pollutant discharged on the shoreline are researched using hydraulic and numerical models. Hydraulic model test was conducted under a constant current. Numerical simulation was conducted using ADI-method under cyclic tidal current in addition to the same constant current as the hydraulic model test.