Height of coastal sand banks and sea level change at Japanese beaches

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Bay-mouth barrier, sand spit, and sand and gravel bars, which is extending parallel to the coastline along the seaward end of coastal lowlands, are called "coastal banks" in this report. Generally, it is considered that the top part of coastal banks is formed during the marine transgression term. Using data obtained from Japanese beaches, this report purpose to discuss the relationship between the formation of coastal banks and sea level change of the Japanese coast in connection with the relative height (h) between the top of coastal banks and the landward limit of the backshore which corresponds to the present sea level.It becomes clear that the height of the landward limit of the backshore(BH) is closely related to the grain size of beach material (D) and the number of nearshore submarine bars (N) on the exposed beaches, and that BH is almost constant independent of D and N on the beaches facing the Inland Sea of Japan. It was also proved that there is no correlation between BH and D on the pocket beaches, and that BH decreases abruptly with increasing N, and tends to approach the steady value of 2 m.Based on the result about BH mentioned above, some coastal banks along the Japanese coast were examined about h. Investigation shows that there were four types of coastal banks, i.e., (1)h decreases to the direction of longshore sediment transport, (2)his nearly same at any point along the shoreline, (3)his about 0 (zero) at every point, and (4)h changes in the direction of the shoreline disorderly.It can be considered that type (1)is formed during the regression term of the sea level, type (2)is formed within the short period of time during which the change of the sea level can disregard, type (3)is formed after the sea level settled in the present level, and type (4)is covered with coastal sand dunes.