Ancient and modern fluvial geomorphology of meandering system from upstream area of the Mun River, Changwat Nakhon Ratchasima

Abstract

At the southwestern rim of the Khorat Plateau, the upstream part of the Mun River flows through clastic sedimentary rocks leading to a massive amount of sand was transported via the Mun River to downstream. The Mun Bon Dam was constructed in 1986, and it would be effect more or less on river system. Therefore, the aim of this thesis is to analyze the geomorphological changes before and after the Mun Bon Dam construction. Moreover, the sedimentary facies from geological and shallow geophysical surveys were characterized. The geomorphic parameters was analyzed from series of aerial–photo and satellite image which were taken in 1974, 1986, and 2011. The sinuosity, width and radius of curvature of the river channels were comprehend the channel stability and possibility of cut off or bank erosion process. Medium and Small sized paleo-channel were recognized and their average channel widths were 35 m and 16 m, whereas the Mun River is of 13 m. SI values of two paleo-channel belts are categorized as meandering river system. The channel stability indicated that the Mun River has low rate of erosion for long time with the migration rate of 0.71 to 2.64 m/yr. Shallow geophysical survey was verified with on-sited boreholes along survey lines. Four radar reflection patterns including reflection free, shingled, inclined and hummocky reflections were represented lateral accretion of point bar from GPR survey. Besides, subsurface lithology and channel geometry derived from the different of resistivity from Electrical Resistivity Tomography survey.