FLUVIAL GEOMORPHOLOGY DURING 30 YEARS OF THE MUN RIVER, WESTERN PART OF CHANGWAT BURIRAM

Abstract

Mun River is a very crucial right bank tributaries of Mekong River which has been known for its complexity of meandering. Those geomorphology that are effected by river’s movement and a helical flow are changed during a period of time. The various geomorphologies during different times can be interpreted from aerial photos, maps, and satellite images and measure the intensity of change by using geomorphic criteria calculation. The geomorphic criteria which are used to quantify river changes are Sinuosity Index (SI), Radius of Curvature (RC) and Channel Width (W). All these criteria and their relationship were used for further examine about meander geometry. As a consequence, SI of Mun River during 30 years has increasing from 1.5 to 1.8 which means the modern Mun River becomes more sinuous. The value of channel width average is decreasing from 72.81 to 39.45 m by influence of the increasing of flow velocity. The river has migration rate of 0.5 – 1.8 m/y. Normalization in migration rate and bend curvature (RC/W) revealed that erosion rate from 1976 to 2009 has a tendency to depreciate. Moreover, profiling from 3 different locations, it found lithofacies that predominated Mun River are Sh, St and Sl. Every lithofacies are identify in a sandy group. This information can prove that Mun River in study area was eroded from a pure sandy source associate with Mahasarakham formation. Also, the research was carried out by using a geophysical tool, Ground Penetrating Radar (GPR), to unveil the subaerially structure of point bars. The tool is a non- destructive geophysical technique that invented for shallow subsurface survey. Not only it can explore underneath earth without penetrate and drill to the ground but also it can show image and estimates depth of subsurface object. By using magnetic wave (microwave) and reflection theory, GPR allows to record a near-continuous sedimentary structures. 8 GPR survey lines from 2 sites achieved by using 200 MHz antenna attached with an odometer based survey wheel for distance tracking. 8 GPR radar facies were recognized to expose variety of sediment characteristics e.g. channel fills, side bar deposit and sand beded. The results from GPR interpretation indicated the complexity of braided characteristic under point bars. Therefore, it can conclude that point bars have developed from mid-channel bars.