ARTIFICIAL RESORT BEACH PROTECTED BY OFFSHORE BREAKWATERS AND GROINS

Abstract

In Japan, area of natural beaches has decreased in the vicinity of cities, towns and villages, in consequence of constructing ports and harbours, reclamating shore and beach, and building strom-surge prevention structures like sea dikes and sea walls. On the other hand, the demand of people for recreation area is increasing year by year with the improvement of living and economic conditions. Therefore, since several years ago, local governments have extensively been constructing artificial beaches and restoring eroded beaches on many places by the aid of the central government. Such artificial beaches, however, need large amount of natural sand, in spite of the deterioration of sand supply and the soaring of sand price. Moreover, local governments are able to get subsidiary payments of the central government for the construction of artificial sand beach, but not for replenishing sand lost by wave action after the completion of the construction works. Therefore, most artificial beaches in Japan are usually protected by groins and offshore breakwaters in order to retain artificially filled sand. But in summer when sea is in calm condition, pollutant produced by sea-bathing people or discharged from the land is likely to stagnate in the vicinity of the shoreline on account of such structures. From the above-mentioned, coastal engineering problems on construction and restoration of sand beach in Japan are: (1) suitable arrangement of offshore breakwaters and groins from standpoint of artificial beach protection (2) keeping the sea water of the beach clean (3) estimation of profile change of the artificial beach due to wave action after its construction. This paper presents the results of investigations conducted with the aim of solving the above coastal engineering problems related to artificial beach constructions at Suma and Ito beaches. The investigations are mainly conducted using model experiment.