The Impact of the Installation of an Estuarine Dam on Sediment Distribution and Accumulation in the Geum Estuary, South Korea

초록

Geum River is the third-longest river in South Korea. Prior to the 1994,the Geum River had an active river-mouth estuary with an upstream saltwedge. In 1994 the Geum River Dam was installed 9 km upstream fromthe mouth of the river, within the lower estuarine portion of theriver. The installation of the dam converted the system into a short tidalbasin with dramatically reduced tidal prism, an artifi cially modulatefreshwater infl ow, generally eliminated salt wedge dynamics, andreduced the tidal prism by approximately 54%. Analyses of a series ofsediment vibracores collected both upstream and down-stream of thedam were analyzed for grain size distributions and analyses ofexcess 210 Pb and 239+240 Pu geochronologies were analyzed for selectcores. Analyses of seven cores reveals that there are three stages to thesedimentary history recorded in the cores: 1) pre-dam installationconditions, 2) transitional condition, which occurred after the installationof the dam during the period when the reservoir was fi lling with waterand there was no sluice gate release of water or suspended sediment,and 3) post reservoir fi ll, when water and suspended sediment werereleased from the dam. Above the dam, coarse sediment that wouldhave been deposited in the mouth of the estuary is instead trapped inthe upper arm of the estuary, and fi ner sediment rapidly accumulates atthe face of the dam. Below the dam, rather than coarse fl uvial sedimentaccumulating, fi ne sediment rapidly accumulates due to the removal ofthe bedload from the post-dam sediment budget of the estuary.