Estimation of siltation rate in the Incheon North Harbour, Korea

초록

The construction of the North Harbour, Incheon, Korea was initiated on the macro-tidal flat from 1997 and completed in 2012. The tidal flat was 2 m high above the ALLW (Approximately Lowest Low Water) before the construction, while the planning depth for the navigational safety was designed -14 m below ALLW. The dredging has been periodically performed to maintain the safe nautical depth of -14 m. As part of efforts to reduce the siltation in the North Harbour of Incheon, sedimentation rate was estimated using four hydrographic sheets (1959, 1990, 2006, and 2013) of Korea Hydrographic and Oceanographic Administration, and amounts of dredged volume obtained from Incheon Regional Oceans and Fisheries Administration. Two gravity cores were also obtained for the accurate siltation estimates. For deeper insight of siltation mechanism in the North Harbour, two ADCPs were deployed at the entrance and inner harbour over a month to measure profiles of flow velocity and suspended sediment concentration. In addition, two CTD surveys were performed twice over 13 hours at two ADCP stations. The CTD survey included OBS, LISST and water sampling at three vertical layers (surface, middle and bottom). The calculated sedimentation rates by two different methods agreed well each other and have a wide range between 20 cm/y at the inner harbour and about 100 cm/y at the harbour entrance. It is inferred that the net horizontal entrainment of the suspended sediment into the harbour occurs more dominantly at the harbour entrance than the inner harbour, resulting in the high siltation at the harbour entrance. On the other hand, the high resolution EFDC numerical model shows the clockwise eddy during the flood in spring tide, which is responsible for the high siltation at the harbour entrance.