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 part of four-year (2010-2013) research program, ‘Development of Integrated Estuarine Management System of Korea’, a series of field experiments have been conducted to understand sedimentation process, especially the governing processes of source, transport and sink of fine sediments, in the altered Yeongsan estuary. 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, LISST and floc camera 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 andtransport of freshwater and sediment. Most of the discharged sediments from the river were fine sediments in the form of flocs. The discharged fine sediments were transported in the surface freshwater layer above the stratification. The flocs settled down further offshore where stratification weakened, and returned landward by tidal currents, causing sediment accumulation near the estuarine dam. Consequently, the Yeongsan estuary underwent high rates of sediment accumulation up to 10 cm per year.