FLOW CHANGES IN THE SETO INLAND SEA DUE TO COASTAL LANDFORM CHANGE

Abstract

 Coastal development in the Seto Inland Sea(SIS) has been underway since before 1900, and the reclaimed area will continue to expand. Coastal land reclamation affects the flow and transport of water and nutrients; therefore, understanding how reclamation affects the surrounding marine environment is necessary. When coastal development is undertaken, environmental assessments are conducted, but they analyzed the impact of land reclamation at local scales to assess its influence on coastal environment; however, don’t analyzed at large spatial scales. However, in SIS, which is composed of multiple bays and nadas, there is a possibility that the effect of landform changes extends to adjacent area. In this study, we analyzed the effects of coastal landform changes on the flow in SIS using a 3D hydrodynamic model that could resolve the topography in detail with unstructured grids. The calculation results showed that the differences in temperature and salinity distribution were localized in many areas, while in Osaka Bay, the spread of river water changed and the differences were significant. Analysis of the effect on tides showed that the resonance condition with the M2 tide was strengthened by the decrease in the natural oscillation frequency period. In additions, the decrease in the amplitude in Osaka Bay reduced the water exchange between Harima-nada, and changed the scale of counterclockwise circulating current in the central part of Harima-nada. The results of this study show that tidal currents have changed over a wide area due to past and present landform changes, and that the influence of human activities on the sea area is significant. We suggest that future coastal development should be carefully considered, paying attention to the impact of human activities not only on local scales but also large scalese.