In Suma Beach of Kobe City, artifical beach nourishment have deen conducted as well as construction of groins and offshore breakwaters which aim to prevent nourished sand against wave action. But, the construction of groins and offshore are feared to impede smooth circulation of sea water and to cause water pollution. This paper discribes the rusults of hydraulic model tests conducted to investigate the influence of groins and offshore breakwaters against exchange of sea water between the inside and outside off offshore breakwaters.
　The model is 1/100 in scale horizontally and vertically. In the model, are reproduced a constant current and small waves in summer season. The dispersion of dye and the current are measured in various arrangements of groins and breakwaters. As a results, construction of groins and breakwaters have been found to accelerate exchange of sea water between inshore and offshore more then tha present state without beach nourishment if thier structure and arrangement are suitable.