有明海

A numerical simulation model has been developed to evaluate the effect of nori aquafarming grounds on the tidal currents in the Ariake Sea coastal waters. The Ariake Sea, a typical semi-closed bay located in the Kyushu Island in Japan, is very rich in many marine products, including nori. Numerous nori aquafarming grounds are installed in the coastal waters of the Ariake Sea during winter. A twodimensional depth-integrated model developed by integrating the three-dimensional continuity equation and momentum equations has been used to simulate tidal currents in the Ariake Sea. Because the maximum tidal variation in the Ariake Sea is approximately 6 m, a wetting and drying scheme is incorporated in the model in order to simulate the emergence and disappearance of tidal flats. Numerical simulations have been carried out using the data pertaining to the actual water depth, observed river inflow rates, wind fields calculated by using a mass-consistent model, sea-water levels calculated at open boundaries, and the actual distribution of the aquafarming grounds and installation density of aquafarming equipment. To validate the model, the simulation results are compared with the observed data at six points in the coastal waters. The velocities and directions of the simulated tidal currents are in good agreement with those observed data. Nori layers growing in the aquafarming attach themselves to nets supported by rods at the sea surface in the Ariake Sea; sufficient tidal current velocity and nutrients supply are absolutely essential for obtaining high quality of nori products. The optimum arrangement of the aquafarming grounds and optimum installation density of the aquafarming equipments have been investigated by numerical simulations performed using the developed simulation model in various assumed scenarios. On the basis of the simulation results, the optimum aquafarming ground arrangement and installation density are decided from the viewpoint of the tidal current velocity.