To study the flow structure arround natural reef, Water flume experiment was carried out. The following results were obtaind. 1) Granulor dye scattering method was very useful to visualize the flow pattems arround a three-dimensional obstacle. 2) The mechanism of upwelling vortex generation is completely different between two-dimensional model and three-dimensional model. 3) An obstacle whose length is between 6 and 8 times of its height generates strong upwelling vortex behind its recirculating zone. The height of upwe11ing vortex is more than 4 times of the height of the obstacle. 4) Dual cones type model generates strong upwelling vortex effectively compared with other mound type model. The tidal currents associated with temperture and salinity fluctuations have been observed at Nomi Bay.
