A Study on Stimulation of Tidal Exchange of a Closed Sea

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Closed sea areas in Japan were classified into several groups by the closed index, which was defined by the ratio of the sea surface area to the cross-section area of the mouth of the closed sea. A local fishing port was considered for the realistic application of the stimulation of the tidal exchange of the closed sea area. A numerical simulation program was developed with the tracking particle method for the visualization of the flow and the preliminary calculations were conducted in a rectangular port. The remnant function was obtained by the number of the remaining particles in the port. The averaged residence time was calculated from the remnant function of the port in the studies of 1999.A local fishing port in Seto inland sea was taken as an example of the closed sea area. Stimulation of the tidal exchange was examined by the introducing a opening in the breakwater which surrounds the port. The remnant function and the averaged residence time of the port were calculated for some positions of the opening in the breakwater. The particle tracking method is applied to simulate and visualize the flow inside the port using a number of imaginary particles. From those numerical results, the effects of the opening in the breakwater on the stimulation of the tidal exchange were confirmed. The determination method of an optimum position of the opening in the breakwater should be established in the future.A similar method was applied to study about tidal exchange of the Hakata bay of Fukuoka city, where Wajiro tidal flat is located at the back of the bay and is valuable as a sanctuary for wild birds. We proposed the construction of a waterway through the sandbank from the outer sea to the inside of the bay. The flow in the waterway would be driven by the tide and be controlled to generate a one way current. These effects on the tidal exchanges were studied using numerical simulations.