Abstract
The Kanmon waterway is one of the most important international routes in Japan. Nowadays, the depth in the waterway is maintained at 13m and will be dredged deeper to enable the navigation of larger ships. Some parts of the Kanmon strait are remarkably narrow and curved considerably. Such geographical features induce rapid and complicated tidal currents in the waterway. Consequently, sand waves as well as continuous sediment accumulation occur in the waterway, and the dredging to keep the required water depth has been prerequisite. MLIT (Ministry of Land, Infrastructure, Transport and Tourism) has been continuing the yearly survey of bathymetry in the Kanmon waterway since 1974. Especially, at four areas where the sand waves are formed frequently , the survey has been conducted several times a year.
In this study, for the purpose of clarifying the characteristics of the sand waves in the Kanmon waterway, bottom topography changes were investigated in detail focusing on Tanoura area where the sand waves are formed remarkably. First, bottom topography in Tanoura area was analyzed by using a GIS, and the motion of sand waves was extracted. Next, the traveling direction of the sand waves was examined by applying PIV(Particle Image Velocimetry). Then, the characteristics of the sand waves, i.e. sizes, moving velocities, occurrence frequencies, etc. were investigated along some cross sections which were set on the basis of the results of PIV analysis. As results, the characteristics of the sand waves were clarified. For example, the moving velocity of the sand waves is about 0.2 to 0.8m/day, and the occurrence frequency is approximately 20 to 45 months.
