Chapter 9 - Applications for Horizontal-Slice Inversion

Abstract

The Nekoseto Channel is located at the central part of the Seto Inland Sea, Japan and displaced northward by 20km from the main shipping traffic route of the inland sea connecting Japan and China and Korea. In the inland sea with the east–west length of about 450km and the mean depth of about 40m, relatively strong tidal current is generated around the central part of the inland sea through a resonance of semidiurnal tides with the first-mode seiches occurring in the entire east–west-sided channel of the inland sea. In the Nekoseto Channel, tidal currents are directed eastward at the flood tide and westward at the ebb tide. The bottom topography, which is characterized by sand banks and troughs, is constructed by bottom stresses due to a pair of tidal vortices induced by a strong eastward tidal jet, which flushes out from the narrow western inlet during the flood tide. The tidal vortices develop as the eastward current is strengthened, and they reach a maximum size of about 2.5km in 2h after the strongest eastward current. The vortices move toward the narrow inlet at the incipient phase of the westward current and change rapidly with increasing westward currents. The tidal vortex pair in a flood tide is finely photographed from an aircraft flying about 6000m in altitude. Whitish sediments suspended from the seabed by the vortices touching the seafloor serve to visualize them. Steady, residual currents may be directed westward through a tidal process in which the vortex pair develops in the eastward current and the current becomes uniform in the westward current.