In this paper the author describes an experimental attempt to prevent the rapid blocking of a harbor entrance caused by littoral drift in the summer period. This work was conducted at "Seppu", a fishing harbor constructed on a sandy beach in Hokkaido, Japan. This investigation was originally sponsored by the Harbor Section of the Hokkaido Prefectural Office One of the top priority objectives, at that time, was to determine the efficiency of two jetties constructed on the updrift side for the purpose of countering the sand drift. Detailed observations including preliminary model experiments, were made from 1961 to I963 on the general aspects (ie condition and phenomena) of the coast in question. Meteorological data were also compiled together with investigations as set forth by the government. Based on the above, the author finally suggested the utilization of natural forces ie waves, offshore currents etc, by constructing an offshore breakwater to curb the blockage of the harbor mouth. This idea was shown to be adequate at least qualitatively by model experiment with the exception of the troublesome time scale problem. These findings, however, have not been adopted as yet for actual improvement of the harbor at present.
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