Vertical structure of salt and suspended sediment at the macrotidal Han River estuary

초록

Vertical profiles of current velocity, salinity, temperature and suspended sediment concentration were observed during 24 hours of spring tide from October 15-16, 2008 by using ADCP, CTD and OBS at the Yumha Channel of the Macrotidal Han River estuary. The vertical structure of salt and sediment exhibited uniform most of time due to strong shear of tidal currents, although salt and suspended sediment concentration varied 22-30 psu and 200-800 mg/l, respectively, with tidal cycle. However, weak stratification occurred at the surface at the beginning of the ebb and this was resulted from tidal straining. On the other hand, the near-bed region was stratified due to increased settling of suspended sediment during low tide slack. The sediment-induced stratification was broken by the increased shear during the flood. In order to further investigate the near-bed stratification process, a 3D sediment transport model of EFDC was set-up for the Han River estuary. The model reproduced the field observation of salt and suspended sediment concentration and the time-varying characteristics of the vertical structure of suspended sediment concentration. Further analysis of model results indicated that the stratification was initiated by the turbulence damping due to sediment-induced buoyancy.