Restoration-driven shifts in the Nakdong Estuary: Contrasting hydrodynamic and morphological response timescales

초록

The Nakdong River Estuary (NRE) in Korea has been the focus of a restoration project aimed at mitigating some of the long-term impacts of human development. Construction of two estuarine dams and reclamation of about 17 km2 of tidal flats over the past century shifted the estuary from a tide-dominated to a wave-dominated system, producing barrier islands at the entrance and expanding mud-dominated environments. Understanding how the estuary may respond to restoration is essential for predicting recovery pathways and informing sustainable management. This study used a calibrated hydrodynamic and sediment transport model (COAWST) to simulate recovery processes over a decade, for the case where the estuarine dams are opened and reclaimed area reverted to open water. Model results showed that tidal currents would strengthen immediately after this restoration, enhancing sediment transport and promoting the re-establishment of an ebb-tidal delta that progressively replaced the barrier islands, while stronger tidal influence also drove a shift in sediment texture from muddominated to sand-dominated conditions. Response occurred on contrasting timescales: hydrodynamic changes such as tidal amplitude and velocity appeared rapidly, while morphological adjustments including bathymetric evolution and sediment redistribution progressed more slowly, requiring nearly a decade to stabilize. These delayed responses were linked to tidal asymmetry, which reshaped erosion and deposition patterns over time. Overall, these findings demonstrate that, for the specific restoration measures examined here-dam openings and the reversion of reclaimed land-hydrodynamic responses occurred immediately, whereas morphological stabilization was delayed, underscoring the necessity of long-term monitoring and adaptive management.

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