Research on flow field and rehabilitation of aquatic environment in the Ariake Sea

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1)A large scale in-situ observation project was carried out in the overall northern part of the Ariake Sea in summer, 2003. Flow and stratification structures under a strong stratification of density due to heavy rainfalll were obtained. 2)It is confirmed from results of field observations that flow structure at the mouth of the Isahaya Bay depends on tidal condition (spring-neap variation), but strong flow along shore of the Shimabara Peninsula dose not. 3)Decreasing trend of velocity at four points in the Ariake Sea was confirmed. It is considered that the Isahaya sea-dyke affects flow structure from the inner area of the Isahaya Bay to the center area of the Ariake Sea. 4)In-situ observations of tidal current and stratification in overall area of the Isahaya Bay were carried out at neap tide in 2004. As a result temporal variation of 3-dimensional flow structure was obtained. 5)It was confirmed by multi-regression analysis that a flow field in the northern area of the Ariake Sea is … More deeply affected by a wind field. 6)Characteristics of bottom sediment distribution around river mouth of the Chikugo River and coastal area of Saga Prefecture were clarified by grain size and nutrients analysis for core samples of bottom sediment. 7)The sigma-coordinate 3-D numerical model of tidal current cooperated with tidal wetland sub-model was developed. 8)It was confirmed from results of field observations of dissolved oxygen and tidal current at the mouth of the Isahaya Bay that oxygen depression depends on inflow discharge of fresh water from rivers and the Isahaya sea-dyke. 9)The algorithm to estimate a distribution of transparency from a satellite image was developed by using the dataset of field observations. 10)Model and numerical experiments to investigate activation effect of the Bottom Roughness installed in the Ariake Sea on tidal exchange was carried out. The tidal exchange between the northern area and the southern area can be restored to the original state before constructing the Isahaya sea-dyke by this method. 11)Upwelling current by the Bottom Roughness was confirmed by a prototype experiment in the Isahaya Bay. Less