Breakdown of Stratification and Enhanced Tidal Pumping in a Meso-Tidal Bay: Impact of Typhoon on Sediment Dynamics

초록

Typhoons can rapidly modify stratification and local current patterns in coastal and estuarine systems. However, the impact of typhoons on sediment transport mechanisms at event time scales remains poorly understood. An acoustic Doppler current profiler was deployed to investigate impacts of Typhoon Hinnamnor (5-7 September 2022) on sediment transport in Yeosu Bay, Korea. Prior to the typhoon, freshwater discharge from the Seomjin River maintained strong stratification, which supported a two-layer circulation. The typhoon disrupted the semi-diurnal tidal regime and induced seaward flow throughout the water column. Wave-induced bed shear stress increased during the period of maximum wind speed, but suspended sediment concentration remained elevated even after wave forcing decreased. This persistence coincided with strengthened current-induced bed shear stress, indicating that currents, rather than waves, maintained sediment resuspension during the typhoon period. Phase differences between surface and bottom tidal ellipses closely reflected stratification variability and served as a practical proxy. Following the breakdown of stratification, enhanced vertical mixing and increased sediment availability promoted contribution of tidal pumping to total near-bed sediment fluxes from 29% to 54%. Landward sediment flux increased substantially despite bed shear stresses comparable to the pre-typhoon period. These findings demonstrate that typhoon-induced breakdown of stratification and sediment availability can alter sediment transport mechanisms, highlighting how extreme weather events modulate sediment dynamics in a meso-tidal bay.

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