Along-channel Variation ofSediment Flux Mechanisms in a Shallow,Macrotidal Estuary with an Estuarine Dam: GeumEstuary, Korea

초록

During the Holocene, deglaciation and marine transgression drowned river valleys and formed estuaries.During the Anthropocene, humans have altered the forcing and geometry of estuaries. Human impacts,such as the construction of estuarine dams, can have consequences to the sediment fluxes anddepositional rates in estuaries, but these consequences are not well understood. To better understandthe sediment fluxes and depositional rates in an Anthropocene estuary, observations were collected inthe shallow, macrotidal Geum Estuary, Korea, where an estuarine dam constructed during 1983-1988 andwhich began operation in 1994 is known to have resulted in enhanced deposition. Observations werecollected over a neap-spring cycle by six Acoustic Doppler Current Profilers (ADCPs) along the 22 kmmain channel and by one ADCP along the 10 km distributary channel which bifurcates 8 km seaward ofthe estuarine dam. ADCP backscatter was calibrated with suspended sediment concentration to estimatethe suspended sediment flux. The fluxes were decomposed into correlation flux (on the tidal timescale)and mean-flow flux (on a longer timescale) terms. Results showed that the sediment fluxes at all stationswere directed landward resulting in deposition. The landward correlation flux due to tidal asymmetryduring spring tides was the primary flux mechanism along the main channel. The seaward mean-flowflux during episodic dam discharge was a secondary mechanism which was only important in the inner 8km section. The sediment fluxes were modified by periodic stratification which occurred in the centralestuary, as well as by waves, which were important only during wave events and near the shallow,exposed channel bifurcation. Overall, the evidence suggests that shallow, macrotidal estuaries withrelatively small discharge may experience enhanced landward sediment fluxes and depositional rates inresponse to the construction of an estuarine dam because of the increase in the tidal asymmetry andsettling-sc