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The behaviours of density current were visualised in a simple cylindrical tank and a hydraulic model shaped as Ariake Bay, set in a rotating tank. In both, water was stratified by dissolving salt in the lower layer. In the cylindrical tank, the spread of density current was well parameterised by newly proposed dimensionless numbers. When the Rossby number decreases, we observed that the current was divided into two parts. This may be interpreted as baroclinic instability. In Japan, recently, there is a big discussion on the effect of Isahaya Dyke on the marine ecosystems in Ariake-Bay. We conducted a hydraulic model test and saw the flow difference between the cases with and without the dyke. Also measured was the effect of artificial density current. We found a suitable location for the apparatus for having nutrient-rich water stay at the seaweed cultivation field before it is diffused very much. In addition, we conducted numerical simulations of the above case.

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