금강과 만경강 역과 모래의 비교연구 = Geomorphological investigation on gravels and sands of two rivers ; the Keum and the Mangyung

다국어 초록 (Multilingual Abstract)

This study is to detect, by analyzing gravels and sands, some characteristics of fluvial processes of two rivers: the Keum and the Mangyung, flowing respectively mountains and plain area. With regard to gravel we analyzed petrographic spectrum, roundness and flatness. In terms of sand analysis, we controlled mineralogical spectrum and observed the form and the surface feature of quartz grains. Such procedure permitted us to find out some important facts, available for geomorphological researches of the rivers. Results of gravel analysis revealed that actual gelifraction furnish many rock debris to the Keum, mountainous river. This fact is also reflected by high deviation values of roundness and flatness. The important tributaries of the Keum, such as Daejonchun and Mihochun, may carry little quantities of gravels to main stream. But in case of the Mangyung, plain river, roundness and flatness show relatively low deviation value, due to the decomposition of rocky element in alluvium However, average value of roundness of the two river is high(300-500), compare to the rivers in Europe and humid tropical Africa, owing to frequent fluctuation of discharge in Korea`s river regime. Quartz concentration ratio of the sands ranges 40-87% in the two rivers. However the sands of the Mangyung show relatively low value, because of the dissolution conducted by the interference of tidal salt water. Mineral spectrum of the sands of the two rivers reveals that granitic saprolite of basins is actually important furnishing source of river sands. Exoscopy of quartz sand grains show diverse rounded forms(from the angular to the well rounded) and variable surface feature(transparent, matte, iron coating...). However, the mattes and the iron coating are apparently more frequent in the samples of the Mangyung, due to red soil of the regions and to it`s geographical conditions favorable for aeolian processes and dissolution by salt water.