Longshore Migration Of Shoreline Mega-cusps Observed With X-band Radar

摘要

Intertidal morphology was monitored continuously with an X-band radar at the research pier HORS in Hasaki, Japan. Hourly-averaged radar images were processed to observe longshore distributions of shoreline positions. Variations of longshore mean shoreline positions and their fluctuation intensities observed in the years 2005 and 2006 showed a seasonal change which followed the so-called beach-cycle. Longshore pixel intensities close to the waterline were extracted from time-averaged images for every hour of the two years to process longshore time-stack image. Longshore migration speeds of shoreline mega-cusps were estimated by cross correlation analysis of the time-stack image, and the reliability of the method was checked. Migration speeds were compared to measured longshore current speeds at the pier and the longshore component of the wave power, showing that they are highly synchronized for most conditions. Finally, the migration statistics were related to the wave data, and the results showed that the northwards migration rates were typically larger than southwards rates, which was consistent with the statistical results for wave forcing variables. Also, the relationship between the migration speeds and the forcing variables indicates that the migration was more active when the wave incidence angle was close to 45°.