Tidal pumping and advective sediment fluxes seaward of an estuarine dam: Geum Estuary, Korea

초록

The Geum estuary dam, which was completed in 1994, resulted in episodic freshwater discharges, tidal current reduction, and enhanced sedimentation at the estuary head. To better understand the sedimentary processes in altered estuaries, such as the relative roles of macrotidal and fluvial forcing and the sediment flux magnitude, acoustic current profilers were moored 1.5 km and 6.5 km seaward of the estuarine dam for two neap-spring cycles during which six episodic dam discharges occurred. Suspended sediment concentration was estimated by acoustic backscatter and sediment flux was decomposed into tidal pumping and nontidal advection fluxes. Results indicated landward transport at both moorings with a negative flux gradient indicating deposition. Tidal pumping near the bed was the main mechanism for sediment transport while advection contributed 16% to the landward flux. Most of the flux occurred during spring tide and was negligible during neap tide. Dam discharge episodically caused advective flux in the middle and surface of the water column of greater magnitude than tidal pumping, resulting in 5,000 kg m flux seaward. However as discharge durations were only a few hours, cumulatively the episodic seaward flux due to dam discharge did not exceed that due to continuous landward tidal pumping. The cumulative flux was estimated to be 23,000 kg m per neap-spring cycle. As non-discharge advection was observed to be relatively weaker and unsteady near the estuarine dam, this study suggests estuarine dams can cause a net decrease in advective fluxes, allowing landward tidal pumping fluxes to dominate in macrotidal regimes.