Wave-driven sediment suspension during slack in the tidal channel of Gangwha tidal flat, Korea

초록

Tidal flats of Incheon, Korea are located off the coast of the Han River mouth. The extensive macrotidal mud flats, for which tidal range exceeds 9 m, are unique in that freshwater discharge during the summer wet season influences the region, while strong waves dominate resuspension and transport processes during winter. A field campaign initiated to better understand imparting influences of these processes and a benthic pod was deployed in a tidal channel in Southern Gangwha tidal flats during November, 2006 and Septermber-October, 2007. Instrumentation on the pod includes one Acoustic Doppler Velocimeter, one Acoustic Backscatter System, and two Optical Backscatter Sensors. During the normal conditions, sediment suspension mainly occurred during the accelerating phase of flood and ebb. Thus, sediment flux is directed landward over a tidal cycle. On the other hand, when waves were stronger, wave-induced shear appeared to support sediment suspension even during the slack after the flood. The sediment flux under strong waves is offshore due to high flux right after the high slack. Considering that high waves occur only about 2% of time over the year, this mechanism of sediment flux is responsible for long-term accretion of Gangwha tidal flats.