Hydromorphological changes of Chi river, mueang district, Khon Kaen province

Abstract

This thesis focuses on the analysis of hydrology coupled with geomorphology for river management such as flood mitigation and river restoration. Morphological Quality Index (MQI) is used for assessing hydro-morphological conditions from part of the Chi River (67 km long) at Khon Kaen province, a major river in north-eastern Thailand. This study area has been suffering from unexpected and repeated flooding. MQI is applied to evaluate the degree of hydro-morphological alteration in terms of relative scores (from 0 to 1). Basically, in case that MQI score equals 1, it means the area has no any alteration. On the other hand, if MQI score equals 0, the area has maximum alteration. The objective aimed at evaluating hydro-morphological conditions from 5 periods: 1952, 1988,1992, 2006, and 2020. The other relative geomorphic indexes were used to describe river planform including sinuosity index (SI), widening rate of channel width and migration rate of the river. Field survey and channel profiles were conducted. As a result, the natural migration rate of Chi River was calculated as average 0.725 m/year. MQI in the study area ranges from 0.84 to 0.63 indicating that the area owns a degree of alteration from minor to moderate alteration. However, the other geomorphic indexes from river segments shows high alteration. The maximum widening rate is 11.08 m/year in the area where sand mining in the river was observed. In place where a dam across the Chi River was constructed (1988-1992), maximum migration rate was up to 90 m/year and SI value had changed from 1.53 (in 1952) to 1.02 (in 2020). This indicates that the construction of dam has changed river direction and river planform. High geomorphic index alteration will correspond with many areas that were altered by artificial construction (low score of MQI). It suggests that artificial construction in the study area has more impact on river alteration than a natural process. The analysis in change of MQI and other geomorphic indexes from this study confirms the need of hydro-geomorphological research that can be applied for future prediction and protection from flooding and river restoration.