Geomorphic criteria for distinguishing and locating abandoned channels from upstream part of Mun River, Khorat Plateau, northeastern Thailand

Abstract

In order to develop geomorphic criteria for distinguishing and locating abandoned channels and meandered belts, in this paper we examined geomorphologic characteristics from the Mun River, one of the main rivers in the Khorat Plateau, northeastern Thailand. Upstream of Mun River originated at southwestern rim of the Khorat Plateau where the river now cuts through sandstone basement. Meandering process shaped meander from upstream ending at low-lying plain about 30 km downstream from the Mun Bon Dam reservoir, and this process displays given values of geomorphic parameters including sinuosity index (SI), channel width (W) and radius of curvature (Rc). Sinuosity index was calculated to express the sinuosity of the channel. The relationship between W and Rc helps to predict channel stability and also comprehend the possibility of cutoff process. As a result, paleo- and recent flow directions of the Mun River are similar from southwest to northeast. Geomorphic parameters from eight river reaches have changed through time since 1974–2015. Two abandoned channel belts were identified, and they own an average channel width of 35 and 16 m, whereas the Mun River nowadays is of 12.7 m. SI values of two abandoned channel belts are categorized as meandering river system. Relationship between meander migration rate and bend curvature suggests that the Mun River possesses low erosion rate between 0.71 and 2.64 m/year since 1974 to the present. This rank of Rc/W ratio suggests stable state of river bank migration. Different migration indicates discontinuous meandering process from individual belt. Lateral migration rate was also decreased after Mun Bon Dam was constructed upstream.