A PROJECTION-TYPE SOUNDER

Takeshi Ijima

Abstract


The Depth sounding is the fundamental process for the investigation of sand drift on sandy beach and has been carried out by means of echo-sounders. Although it is necessary to obtain the actual variations of bottom topography under the direct action of strong waves, the data even by the up-to-date method of soundings are limited to the case of calm sea conditions. Moreover, even in calm seas it is often difficult to measure the depth of water in the surf zone which has remarkable change of bottom topography due to wave action. The author has no information on the data of bottom topography under the direct action of waves on actual beaches in Japan, excepting those of Mr. Fujiki on the coast of Niigata along the Japan Sea, who, however, had measured the bottom profile along one fixed line which was set perpendicularly to the beach. At present we have no effective method of measuring the amount of drift sand, and therefore the measurement of dynamical variation of bottom topography is considered to be the possible primary and fundamental approach to the estimation of sand drift on sandy beach without any coast structure and also to be the final method of finding out the similarity law between model test and actual phenomena, through which model test may become a confiderable method of solving the sand drift problem. In order to observe the dynamical varation of bottom topography by wave action, it is necessary to develope newly any possible method without boat and echo-sounder. This is the purpose of study of projection type sounder.

Keywords


depth sounding; sediment transport; echo sounder

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