Flood and ebb dominance in estuaries in Korea

Ebb dominance, which is mainly observed at the Youngsan River estuary (YRE) and flood dominance at the Keum River estuary (KRE) are conspicuous features in the southwestern coastal zones of Korea. In considering the sources of this asymmetry, which include, not only bottom friction, irregular bathymetry and tidal flats, other issues also need to be considered, since dominance occurs extensively in coastal regions near the YRE (ebb) and the KRE (flood). This study concludes that the rotational directions of M2 tidal ellipses at the eastern side of the Yellow Sea can produce the differences between maximum currents in flood and ebb, and thus, flood/ebb dominance in southwestern Korea is closely related to the tidal characteristics of the Yellow Sea. An analysis of Kelvin and Poincare´ waves in the Yellow Sea also indicates that flood/ebb dominance is caused by the southward propagation of an M4 tide while an M2 tide propagates northward, which is another characteristic feature of the Yellow Sea. This reinforces the above conclusion. Flood/ebb dominance, which is generated by these mechanisms at the outer sea, becomes more pronounced landward with an increase in the amplitude of M4 tides. However, the mechanisms involved in the growth of an M4 tidal constituent at the KRE and at the YRE are very different. While flood dominance at the KRE is mainly due to energy dissipation by friction, ebb dominance at the YRE is largely caused by the vast tidal flats. In addition, shallow water tides propagating from the outer sea also serve to reinforce flood dominance at the KRE as well as ebb dominance at the YRE.