Sedimentation of Tidal Currents

在我项目的最后一年，我研究了阿里亚克海潮间带沙洲的沉积，以及太平洋沿岸阿吉古拉海滩附近的更新世潮间带沉积1。有莱克海(湾)内侧广泛分布泥质潮滩沉积，熊本县外海岸发育砂质潮滩沉积。在户户半岛的Toguchiura海滩，我们可以看到十个甚至更多的潮间带沙洲。它们的山脊蜿蜒曲折，与海滩近平行。涨潮时风中的波浪在潮间带沙洲上形成了许多波纹。波纹的峰线与沙洲的脊线倾斜，在沙洲向海的斜坡上，波纹的峰顶在波纹出现前被微弱的波浪作用侵蚀，变圆或变平。向陆地的斜坡上的波浪波纹几乎不受波浪的影响。结果表明，潮间带砂坝部位的波纹产状具有一定的特征。它们的不同作为区分出海方向的标准是非常重要的。我们在Ajigaura海滩发现了更新世阶梯沉积。当一个海岸沙洲在天气晴朗的时候移动到海滩上时，它就变成了一个海滩连接(焊接)的沙洲。回流的水从海滩表面滑下，使焊接的沙洲沉积物变形，形成台阶。我们可以从当时的台阶深度(Z：台阶沉积物的厚度)中得到台阶底面深度(H)，h=1.8Z。由于对台阶沉积物的描述很少，所以我将对台阶沉积物进行描述。

In the last year of my project, I did research on sedimentation of intertidal sandbars in the Ariake Sea, and Pleistocene intertidal sediments near Ajigaura beach along the Pacific coast.1. In the Ariake Sea (Bay), muddy tidal flat sediments are widely distributed at the inner part, and sandy tidal flat sediments are developing along the coast of the outer part in Kumamoto Prefecture. At Toguchiura beach, the Uto Peninsula, we can see ten and more ridges of intertidal sandbars. Their ridges are sinuous in phase and subparallel to the beach. Many wave ripples are constructed on the intertidal sandbars by waves in a wind during high tide. The crest line of wave ripples is oblique to the ridge of these sandbars.The peaked crests of wave ripples on a seaward slope of these bars are eroded with weak wave action just before emergence of wave ripples, and become rounded or flattened. Wave ripples on a landward slope are very little deformed by waves. As the result, the attitude of wave ripples is characteristics at the position of intertidal sandbars. Their difference is very important as a criterion for discriminating the seaward direction.2. We found out Pleistocene step sediments at Ajigaura beach. When a longshore bar moves to the beach under fair weather, it becomes a beach-attached (welded) bar. The backrushing water sliding down the surface of the beach deforms welded bar sediments to make step. We can know the step-base depth (h) from the step depth (Z : the thickness of step sediments) at that time ; h=1.8 Z. As description on step sediments is very few, I am going to describe on step sediments.