抄録
Looking at the results of the surveys taken along the coast of the western part of Enoshima (Kanagawa Prefecture) and of Tokai village (Ibaraki Prefecture), “period” the author found among the intercuspspaces periodical changes the length of which could be called as by the author.
The average length of these periods is about 500 meters, and one period contains many cusps which are arranged in order of length i.e, from long to short and short to long again. Along the shore, longshore bars and troughs are developed. Corresponding to the periods, these bars have been situated in front of the period.
Based on these facts, the author presumes the relation between cusps and long-shore bars as follows:
The wave is reached and, broken on the bar, and plunged into the trough. The strength of the plunging of wave may take the strongest on the center part of the bar and weak on sides of the bar, because the height of the, bar above the bottom of the trough is high at the center and low at sides of the bar.
Consequently, concerning the strength of the swashing on the beach, the front part of the bar is stronger than the side parts of the bar. Accordingly, the huge cusps formed on the beach of strong swashing and minor cusp formed on the beach of weak swashing.
On the western coast of Enoshima the sizes of cusps and bars are larger than on the eastern part, and on the coast of Tokai village, they are larger in the northern part than in the southern part. In the region of Tokai village, the sizes of cusps are inflicted by influences of the banks locating off estuary of Kuji River and they are the shelter against the north_??_eastern wind waves also. In case of Enoshima, however, the reason of difference of sizes of cusp and bars, in the eastern and the western parts, is considered as the loss of energy of wave by the bottom friction.
