大潟海岸・四ッ屋浜の観測桟橋跡周辺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 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. There are several artificial structures like submerged breakwater in Yotsuyahama coast. The coastal area between Naoetsu harbor and Yotsuyahama coast has been suffered from severe beach erosion. Both sounding and sediment sampling on the sea bottom have been carried out in Yotsuyahama coast on June.28 2008, Oct.15 2009, Mar.1, 6 2010, and Aug.17 2010, and Nov.7 2010. The longshore measurement section is about 200m offshore from shoreline, and the cross-shore measurement sections are at the central region and the joint region of a crescent-shaped bar. The sediment sampling has been conducted in the cross-shore measurement sections at interval of 1.0m deep. It was shown clearly that the existence of Observatory Pier has given the full influence to the sedimentation on the sea bottom. 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.