Impact of an estuarine dam on sediment distribution and accumulation in the Geum Estuary, South Korea

초록

The Geum Estuary, located on the west coast of South Korea, provides a compelling case study of estuarine transformation under intensive anthropogenic modification. Following the construction of the Geum Estuarine Dam in 1994, the estuary has undergone marked changes in hydrodynamics, sediment transport pathways, and depositional environments. To quantify these changes, a suite of vibracores was collected upstream of the dam, within the inner estuary, across adjacent tidal flats, and on the inner continental shelf. Grain size distribution, sediment geochemistry, and radionuclide-based geochronologies (Pb-210 and (239)+Pu-240) were used to reconstruct depositional trends and assess sediment retention dynamics. The results demonstrate a pronounced shift from sand-to mud-dominated environments downstream of the dam, with sedimentation rates reaching 6-8 cm/yr(-1). In contrast, formerly mud-rich offshore zones now exhibit sandier stratigraphy and reduced accumulation rates, while coarse sediments continue to dominate upstream of the dam. These patterns are consistent with the similar to 54 % reduction in tidal prism and the dam's top-gate discharge design, which restricts bottom flows and promotes trapping of suspended sediment within the estuary. Seasonal processes such as strain-induced periodic stratification and episodic dam releases further reinforce sediment convergence in the inner estuary. This study highlights the long-term legacy effects of river regulation on estuarine sediment dynamics and pollutant accumulation. The findings have broader implications for the management of dammed estuaries in monsoon-influenced regions. The Geum Estuary serves as a critical reference for evaluating sedimentological consequences of human interventions in estuarine systems globally.

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