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ABSTRACT Woo, S.-B. and Yoon, B.I., 2018. Numerical simulation of fortnightly modulations of the convergence zone by residual volume transport in a macrotidal estuary. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 606–610. Coconut Creek (Florida), ISSN 0749-0208. This study examines the fortnightly modulation of convergence zone by residual volume transport of main channel using a numerical model in the tidally dominated Han River estuary (HRE), South Korea. The numerical model, EFDC (Environmental Fluid Dynamics Code), was simulated for 124 days, from May to August 2009, and used observed freshwater discharge for major rivers of HRE. The residual volume transport discharged into the HRE from the Yeomha channel and Seokmo channel had a ratio of 44:56 over thirty days under normal freshwater conditions. The model results show that a temporal variation of the residual volume transport (Lagrangian transport = Eulerian transport+Stokes transport) is formed near the Yeongjong Bridge with spring-neap variability, and net transport is outflowed to the west through the channel between Ganghwa and Yeongjong. Due to magnitude change of the residual volume transport by fortnightly (spring-neap) modulation, convergence zone (junction location of residual volume transport) show upward and downward spatial variation. We found that the convergence zone moves downstream during the spring period because of; 1) strong net downward barotropic flow by increased sea level difference between upstream and downstream during the spring tide; 2) decreased baroclinic flow towards the upstream of the main channel, caused by intensified tidal mixing during the spring period; and 3) increased outflow through the tidal flat channel between Ganghwa and Yeongjong during the spring period. [ABSTRACT FROM AUTHOR]

The Yellow Sea is fringed with deltas and estuaries on the Chinese and Korean coasts, respectively. The Korean estuaries, rock bound on the Ha coast, are represented by the Han estuary, the largest in the eastern Yellow Sea. To reveal the relationship between extensive tidal flats and major channels in the Han estuary, suspended sediment transport was observed from the water column down to the bottom boundary layer. Transecting channels and deploying benthic tripods were accomplished at a number of critical sites during different spring tides, mostly under the fair-weather conditions of dry seasons in 2006-08. The hydrodynamic measurements unraveled the role of macrotidal currents in estuarine suspended transport. According to lateral momentum analyses, cross-channel flows were governed by two forces: rotation and surface slope. The estimations of suspended flux and lateral momentum balance elucidated that, of the two candidate channels, the Yeomha Channel dominantly supplied riverine muds to the adjacent vast Ganghwa tidal flats. The other larger channel, Sukmo, was found to displace muds up the channel to the Han River mouth. Another offshore major channel, Jangbong, revealed small suspended flux, reflecting no substantial mud input of offshore origin into the Han estuary. This study maybe timely in that most Korean estuaries have artificially developed and are facing various environmental problems. [ABSTRACT FROM AUTHOR]