Changes in tidal currents in the ariake sound due to reclamation

The Ariake Sound is a highly productive estuary located in the western part of Japan. The decline in fisheries and the frequent occurrence of red tides and hypoxia indicate a deterioration in the ecosystem of the sound. A change in tidal currents, which is one of the possible causes of the deterioration, was investigated by numerical experiments. Two major changes in the topography of the sound, which may have changed the tidal currents, are examined. These are the reclamation in the innermost part of the sound and the construction of a dyke in a subembayment called Isahaya Bay. The numerical experiments show that the reclamation caused the tidal currents to decrease by more than 10% over a large area in the innermost part of the sound. The influence of the dyke on the tidal currents is relatively local compared to the reclamation; the area where tidal currents significantly decrease is located mostly in the subembayment.