Development of a water quality tank model classified by land use for nitrogen load reduction scenarios
The Ariake Sea, a typical semi-closed bay located in Kyushu Island, western Japan, has a maximum tidal range of 6 m in spring tide, and its vast tidal flats are composed of both sandy bottom areas and muddy bottom areas. In this study, two-dimensional depth-averaged finite difference numerical models have been developed for predicting the tidal flow velocity and suspended sediment concentration in the Ariake Sea. In the suspended sediment transportation model, a time-dependent sediment resuspension and deposition process was modeled as a response to the tidal flow by considering the presence of cohesive bottom sediment. The shifting-particles method, known as an operator-splitting technique, was used for time integration of the convective-dispersion equation. The model results were compared with in situ measurements of suspended sediment concentration and tidal flow velocity at several points in Isahaya Bay—located at the western part of the Ariake Sea—and also with the estimated suspended sediment concentration distribution via a Landsat Thematic Mapper image. The results indicated that the models were able to predict the measured values for suspended sediment concentration and tidal flow velocity, as well as the spatial distribution pattern of the suspended sediment concentration as estimated by the Landsat Thematic Mapper image.