Seasonal sedimentary processes on macrotidal flats in Garolim Bay, west coast of Korea

Abstract

The sedimentary processes on the western tidal flats of Korean Peninsula are directly influenced by monsoons and heavily affected by waves in winter and tidal currents in summer, resulting seasonal deposition and/or erosion of sediments. Garolim bay is typically a semi-enclosed bay with wide tidal flats which occupy about 77% of the bay surface. The tidal channels at the entrance distribute on either side of the ridge. Tidal currents are flood dominant on the eastern side and ebb dominant on the western side. Generally, sandy sediments dominated over the bay mouth, whereas sand-mud mixed sediments covered in the middle and inner bay in summer 2014. In comparison of surface sediment distributions in summer 2002 and 2014, the area of sand and muddy sand sediments extended from the outer to middle bay and the percentages of mud increased in the inner bay in summer 2014. The short-term sedimentation rates from February 2014 to February 2015 showed that the erosion was dominated on the tidal flats at inner (EU-Line) and outer bay (DG-Line) during spring and winter with net erosion rate of -1.55 mm/year and -55.23 mm/year, respectively. In the tidal flat at middle bay, the deposition occurred on DS, DD and SM-Line with net deposition rate of 18.94, 6.65 and 4.85 mm/year, respectively and the erosion was dominated on JW-Line with net erosion rate of -14.80 mm/year. The calculated sediment transport vectors with grain-size parameters showed that the sediments transported eastward and then deposited on east side of middle bay at Hwanseongri and Doseongri tidal flats in summer 2014. Based on these data, the sediments enter into the bay through the eastern channel of the bay mouth by tidal current mostly deposited in tidal flats at middle bay from spring to autumn. However, in winter, sediments in tidal flats at outer and middle bay transported to inner bay by wind wave and tidal current, resulting deposition sediment in the tidal flat at inner bay.