SEASONAL CHANGES OF SEDIMENT CHARACTERISTICS ON TIDAL FLAT IN GEUNSO BAY, WEST COAST OF KOREA

Abstract

Geunso Bay, located in Taean of the western Korean Peninsula, is a semi-enclosed bay type with a mean tidal range of about 6 m. The tidal flats are largely developed all along the side of the bay. Digital elevation model showed that 95% of the total area of the bay was tidal flat. The surface sediments in the bay consisted of mainly muddy sand and were classified into five sedimentary facies in winter and summer 2009. The short-term sedimentation rates were determined by burying a plate at sub-bottom depth and periodically measuring in sediment depth between the surface and plate. In the eastern tidal flat, the annual sedimentation rates were ranged -71.3 to 12.4 mm/year with net erosion rate of -15.0 mm/year. The erosion was dominated on the tidal flat at middle bay, while the deposition occurred on the western tidal flat during winter and spring with the net deposition rate of 10.8 mm/year (Figure 1). The suspended sediments were supplied relatively a large amount into the bay in winter and spring and were transported in anti-clockwise direction. Sediment transport paths were calculated using grain-size parameters of the surface sediments in winter 2009. The resultant sediment transport pattern showed relatively predominant westward transport vectors in the tidal flat. The winter waves played a limited role in the seasonal variation of sedimentation due to the southwestwardly opened bay mouth. It seems that the supply of suspended-sediments and circulation pattern of tidal currents are most important for seasonal variation of sediments on the tidal flat.