Wind-Induced Water Exchange between Stratified Basins

Water exchange between lnohanako Estuary and Hamanako Bay, Japan with density stratification is investigated using the field data. The basins are connected by a narrow channel with length 200 m through which waters and nutrients are exchanged between them. The principal axis of channel between two basins is located nearly in the north-south direction, thus it is natural that the water flow between the estuary and bay is influenced more by the north-south component of wind than the east-west component of that. Although the relationship between water exchange and the east-west component of wind is relatively low compared with the north-south component, the water exchange is controlled by this. In this study, using the field data measured by ADCP and CTD in summer months of 2009, a mechanism of wind-induced water exchange was investigated and discussed. A simple theoretical approach suggested that the dynamic response of density surface in Hamanako Bay to the wind force caused the circulating flow in the channel. The change of water density was more remarkable in Hamanako Bay than in Inohanako Estuary in response to the wind direction, and the surface layer in Hamanako Bay became thinner during the westerly wind. This study shows that the water exchange associated with the east-west wind is caused by the difference of water pressures between Inoahnako Estuary and Hamanako Bay, which is induced by the fluctuation of density interface between the surface and bottom layers due to wind.