Field Observation of Tidal-Exchange Through Straits from Deterministic View Points and Consideration of Methods to Control the Process

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Abstract
Tidal-exchange phenomena at straits were investigated from a deterministic view point. Coherent structure theory was used to analyse the turbulent boundary layer formed by tidal current through straits. Remote-sensing technology from airplanes and Landsat were introduced as a flow visualization method, which enabled the coherent structure theory to be applied to such a large scale turbulent flow in the field. Onsite study was practiced at Naruto, Tomogashima and Akashi Strait which connect Seto Inland Sea with open sea. Aerophotographic survey at Naruto Strait presented the existence of the coherent vortices in the free boundary layer of the tidal current and amalgamation process between them. MSS data from Landsat was analysed to reveal the existence of the large scale vortex and its formation process, namely amalgamation process of the small scale coherent vortices. This formation process of large scale vortices via the stage of small scale coherent vortices from vorticity exfoliated at the strait were found to play an important role in the tidal- exchange process and were ascertained experimentally with hydraulic scle model tests. Some practical hints for planning engineering devices to promote the tidal- exchange process were presented experimentally, which suggest that the process may be accelerated by setting some jetties to exfoliate the turbulent boundary layer in order to amalgamate the vortex into a pair of strong large scale vortices. This deterministic approach employed in this paper seems to have more advantage than the stochastic one to give clearer physical image of such a large scale flow phenomena in the field as that of tidal-exchange process at straits.

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