FLUVIAL ENVIRONMENT RESPONSES TO CLIMATIC CHANGES AND HUMAN IMPACTS

In southern part of Korean peninsula, Holocene alluvial or fluvial deposits occupies quite a large surface areas, while the latest Quaternary fluvial deposits are less developed in apparent, except in coastal, old fluvial and hillslope areas. Among the latter case, the most outstanding depositional sequences are latest Pleistocene fluvial wetland deposits. They are filled now in the drowned valleys along the coastal areas or distributed at alluvial plains. This research is aimed to revealing lastest Quaternary fluvial environmental change responded to fluvial wetland in South Korea. The environmental responses to climatic changes and human impacts during the last 17,000 years were analyzed on the basis of organic muds profiles intercalated in fluvial deposits. Several fluvial sites, including Jangheung-ri of Nam rIver, Soro-ri of Miho river, Youngsan rivermouth in Muan, Oksan-ri of Hampyeong and Sanggap-ri of Gochang were selected to examine their sedimentary facies, carbon radiometric age, and pollen analytical data. The terrestrial fluvial sequences show a millenium-scale climatic fluctuations in the fluvial sub-environments, which were represented by the cyclicity of fluvial sands, backswamp organic muds, and flooding muds with paleosols. Pollen anaysis indicates paleo-vegetation change during the last 6,000 up to 15,000 years. Some ancient rices, uncertain of wild or domesticated ones in origin, were found in Soro-ri organic muds dated as old as 14,000years B.P. In general ancient human management of fluvial wetland is inferred from their reclamation practices after 5,000 to 6,000 years B.P in Korea. Frequent reclamation of fluvial wetland made fertile cultivating land at a large extent since the last 1,500-2,000 years. Cyclic inundation, however, made ancient people migrate towards hill side at least above 6.5 m to 7.0 m above local base level in order to avoid flooding hazard. Modern artificial constructions in fluvial areas since the 20th century, including heavy construction of banks, dam and excessive aggregate extraction, have diminished flooding damage drastically. Yet cultivated land has not been fully prevented from occasional high peaks of flooding attacks. Over-managements or artificial rising or decreasing of the equilibrium height of riverbed might be one of causes of artificial flooding damages.