Numerical Study of Tidal Water Mass Exchange in an Inland Sea with Archipelago

The tidal water mass exchange in an inland sea with archipelago is numerically studied adopting the control volume based 2-dimensional finite element method to cope with the complex coastline. Yatusiro Sea situated in the south-west of Kyushu, Japan is the model inland sea of our study. Water mass exchange by semi-diurnal (M_2) tidal flow is investigated by the dispersion of Lagrangean particles and by the Eulerean tidal residual flow. Main results are as follows: i) Except the southern part of Ariake Sea and Nagashima Strait, the most part of Lagrangean particles still stay in the areas after 20 periods. ii) The particles in Ariake Sea (Yatusiro Sea) flow into Yatusiro Sea (Ariake Sea) through Yanagi-seto (Misumi-seto). iii) The particles in Hachiman-seto flow into Yatusiro Sea through Oh-seto and Gannojiri-seto. iv) The particles in the south part of Yatusiro Sea flow into Nagashima Strait through Mebuki-seto and Ikara-seto. v) In the Eulerean tidal residual flow, there exists a clock-wise vortex around Shishijima island in Yatusiro Sea.