Characteristics of Environment and Tidal Current in the Ariake Sea

摘要

In recent years, the Ariake Sea in the west of Kyushu Island has been suffered tornenvironmental problem such as red tides. This paper presents two major approaches inrnrelation to the change of environment in the Ariake Sea; one is analysis on the water qualityrnand meteorological variables using past observed data, the other is numerical simulationrnbased on two-dimensional model. Through the analysis on the water quality, it was found thatrnan oxygen depression, an important factor for the outbreak of the red tide, has been occurredrnat bottom layer in the head of the bay since 1970s. In this numerical experiment, followingrnresults were obtained: 1) a vibration cycle became shorter by about 20 minutes, after thernshutoff in Isahaya Bay, 2) the local circulation inside the shutoff bank evolved due to controlrnof water gate, 3) after Kumamoto Port built, the drift of a current around the port changed byrn20-30cm s~(-1), and 4) the drag induced by seaweed crop nets made fairly decrease of drift of arncurrent in center and inner part of Ariake sea.