2次元数値モデルによる有明海奥部の潮汐流の流動特性の検討 : 諫早湾潮受け堤防の影響評価

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In order to clarify the effect of the embankment of Ariake reclamation project to the water quality of Ariake sea, tidal flow was computed by the two-dimensional numerical simulation and flow characteristics around the bay head were investigated. The discharging rate and the residence time of sea water of the bay head were determined, utilizing tracer particles and a passive scalar function. It was found that the discharge of sea water from the bay head consists of two phases. The discharging rate in the first phase increases faster than that in the second phase and its magnitude changes in the effect of the embankment as well as the tidal amplitude. On the other hand, the discharging rate in the second phase is almost independent on such parameters. The cause of the differences between the two phases was investigated through the study of the flow structures. At the boundary region between the bay head and the center, there exists a circular residual flow. The sea water of the bay head is transported by the flow to the bay center, immediately after the initiation of computation. Then, the discharging rate exhibits the rapid increase. The variation of the discharging rate by the embankment is probably due to slight change of the location of the circular residual flow. It is the reason why the discharging rate in the first phase shows above mentioned characteristics. Consequently, it was concluded that the discharging rate in the first phase do not represent the real tidal exchange. During the first phase, the area of the circular residual flow is filled with sea water of the bay head, and in the second phase, the discharging rate begins to show the net value of the tidal exchange. Then, residence times were computed from the latter discharging rates, and the values were from 50 to 279 days. The differences depend mainly on the magnitude of the horizontal diffusivity applied in each computation. The contributions of the advection and the horizontal diffusion to the discharging rate are almost same, when the horizontal diffusion constant is set as K=1.0m^2/s. As the horizontal diffusion constants increases, the contribution of the advection relatively decreases. Unlike the expectation, it was not found the trend to prolong the residence time by the effect of the embankment.
2003-03-31

2次元数値モデルによる有明海奥部の潮汐流の流動特性の検討 : 諫早湾潮受け堤防の影響評価

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