FLOC DISCHARGE AND SEDIMENT ACCUMULATION AT ALTERED MACRO-TIDAL YEONGSAN ESTUARY OF KOREA

초록

Macro-tidal Yeongsan estuary of Korea has been altered due mainly to the construction of an estuarine dam in 1981 as well as the reclamation of extensive tidal flats along the Yeongsan estuary. As a result of the presence of an estuarine dam, the Yeongsan estuary underwent high sedimentation at a rate of greater than 6 cm/yr. To understand sedimentation processes of altered Yeonsan estuary a series of field experiments have been conducted. The field campaign includes grain size analysis of surficial sediment, bathymetric survey, coring of bed sediment and subsequent dating analysis. In addition, transport mechanism was investigated by measuring of vertical profiles of flow, suspended sediment concentration and floc size using CTD, ADCPs, and LISST during wet and dry seasons. The construction of the dam caused significant impact to the Yeongsan estuary by blocking estuarine circulation and reducing tidal current velocity. Moreover, the dam operation became the main controlling factor for the discharge and transport of freshwater and sediment. Most of the discharged sediments from the river were fine sediments in the form of flocs. Of the sediment, the content of organic matter was higher, usually 30-40 percent of the total suspended matter. The discharged fine sediments were transported in the surface freshwater layer above the stratification. The flocs settled further downstream where vertical stratification weakened, but horizontal gradient is much stronger, causing high sediment accumulation