大潟海岸・上下浜の海底地形と海底底質の粒度組成 --主に弧状沿岸砂州において--

Abstract

Ogata Wave Observatory, Kyoto University is located in Yotsuyahama coast, Niigata Pref., Japan. Yotsuyahama coast is in the center of Joetsu-Ogata Coast. In this region, Katamachi sand dune develops very much, and the sediment in Joetsu-Ogata Coast is composed of both sand and gravel. Jogehama coast is another coast in Joetsu-Ogata Coast and is in a natural state. The distance between Yotsuyahama and Jogehama coast is about 3.0km long. The seashore between Yotsuyahama and Jogehama coast has been suffered from severe beach erosion. Both sounding and sediment sampling on the sea bottom have been carried out in Jogehama coast on Nov.7 2010, July.27 2011, July.24 2012. The longshore measurement section is about 200m offshore from shoreline, and the cross-shore measurement sections are at the joint region and the central region of a crescent-shaped bar. The sediment sampling has been conducted in the cross-shore measurement sections at intervals of 1.0m deep. The results of data analyses on both the bottom profile and the grain size composition of the sediment on the sea bottom provide some ideas to understand the reasons for the coastal erosion.