Abstract
The largest change in the Ariake Sea before and after coffering by a closing levee in the Isahaya Bay are appearances of a regulating reservoir and intermittent discharge of deteriorated fresh water from it to the Isahaya Bay. People are prone to think that the water discharge from the reservoir flow straight out through the central and the mouth parts of the Ariake Bay and that its impact on the inner part of the Ariake Sea is slight. To make sure of this, we carried out numerical advection -diffusion simulations of conservative substance supplied steadily from the inner part of the Isahaya Bay and made it clear that it stayed in the inner part of the Ariake Sea at high concentration in a steady state. This fact is quite reasonable from the point of view of hydraulics and fluid dynamics. Therefore there is a strong possibility that the deterioration of water quality in the regulating reservoir extends widely over even the inner part of the Ariake Sea.
