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

在本报告中，海湾口屏障、沙嘴和砂砾沙洲沿着沿海低地向海的一端平行于海岸线延伸，在本报告中被称为“海岸堤岸”。一般认为，滨岸顶部是在海侵时期形成的。本文利用从日本海滩获得的数据，讨论了海岸岸坡的形成与日本海岸海平面变化之间的关系，即海岸岸坡顶部与对应于现在海平面的后岸向陆界之间的相对高度(H)。明确了后岸向陆界(BH)的高度与海滩物质的粒度(D)和裸露海滩上的近岸海底坝(N)的数量(N)密切相关，并且在面向日本内海的海滩上，BH几乎是不变的，与D和N无关。在上述结果的基础上，对日本海岸的一些岸滩进行了h左右的考察。调查结果表明，日本海岸有四种岸滩类型，即(1)h向沿岸泥沙输移方向下降，(2)沿岸线任一点几乎相同，(3)在每个点上都约为0(零)，可以认为类型(1)是在海平面消退期间形成的，类型(2)是在海平面变化可以忽略的短时间内形成的，类型(3)是在海平面稳定在现在水平后形成的，类型(4)是海岸沙丘覆盖的。

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.