Dynamics of Sediment Resuspension in the Inner Harbor Under Different Forcing Conditions: A Case Study of Ulsan, Korea

Bottom mooring data of currents and backscatter strength derived from a 1200-kHz acoustic Doppler current profiler were collected in the inner Onsan Harbor, Ulsan during the summer season (July 5 to August 5, 2016). The mean volume backscattering strength (MVBS), which is a proxy of suspended sediment concentration (SSC), continued to exhibit distinct signatures of sediment erosion (or resuspension) under different forcing conditions such as tides, winds, and precipitation. Results exhibit the different patterns of sediment resuspension between spring and neap tides. During spring tide, the extensive tidal forcing provided a favorable condition to resuspend sediments trapped near the bed. The MVBS with high SSC was consistently recorded. During neap tide, on the other hand, the MVBS with high SSC was intermittently recorded, which was related to the strong wind events. While the flow was being intensified by winds, the short-lasting (2-4 hours) sharp spikes of MVBS were observed. The stratification developed by increased precipitation might cause to block the upward transport of sediments near the bed, even though the strong winds (>13.6 m s(-1)) lasted over 4 days. These outcomes could give insight into the complexity of hydrodynamics and sediment transport occurring in the harbor where various natural and artificial forcings are combined.