Comparision of depositional environments between sandy and muddy tidal flats in the tide-dominated coasts, Yellow Sea

초록

The west coast of Korea is characterized by a highly indented shoreline composed of a great number of ria-type bays and nearby island. The coast has extremely high tidal ranges, resulting in extensive development of tidal flat, total area 1,980 km2. This is classified by sandy and muddy tidal flat due to complex factors such as local energy regime, supply of sediment, coastal topography and so on. Especially, sediments of sandy and muddy tidal flat differ from each other in composition and textural characteristics such as mean grain size, sorting and skewness. Textural parameters (mean, sorting, skewness) of sandy tidal flat are relatively coarser, better sorting and negatively skewed distribution than ones of muddy tidal flat. The distribution of surface sediments between sandy and muddy tidal flat shows a typical coarsing and fining in seaward direction, respectively. These can be interpreted to result from hydraulic energy, relative predominance of tide and wave effect, morphology and supply of sediment between two environments. According to C/M diagram, transport mode of muddy tidal flat is mixed 3 mode (bedload, graded suspension and uniform suspension), these are typical sedimentary process in tidal flat. Sediment of sandy tidal flat is transport by forms of bedload and graded suspension. From these results, muddy tidal flat is a typical tide-dominated environment, which tide play an important role of dispersion of wave effect and shoreward transport of offshore sediment. On the other hand, sandy tidal flat show macrotidal beach environment, which is characteristic of redistribution of sediments and seaward transport of fine sediment by relatively strong wave effect.