Impacts of the Sea Dike and Reclamation Project in Isahaya Bay on Baroclinic Structure in the Ariake Sea, Japan

Abstract: In 1997 the Isahaya Sea Dike was built in the head of Isahaya Bay which is a branch of the Ariake Sea, Japan, with the aim of reclaiming land for agriculture and flood control. This study examines how the Isahaya Sea Dike has affected the baroclinic structure and development of hypoxic waters in the Ariake Sea by focusing on the spatial change of freshwater discharge, the temporal change of freshwater discharge and the vertical mixing. To accomplish this modelling in Delft3D-FLOW was used to simulate the three scenarios: conditions without the dike (1), conditions with the dike (2) and conditions with the dike but with the Honmyo River discharge from the North Gate (3). The results show that the spatial change and the temporal change of freshwater due to the construction of the dike has no significant effect on the baroclinic structure in the Ariake Sea. The results also confirms the results by Yano and Nishimura (2014) that the dike has caused weakened vertical mixing in Isahaya Bay. To determine the cause of the development of hypoxic waters in the Ariake Sea further studies are needed.