Analysis of flood susceptibility in Chi river basin, northeastern, Thailand using topographic index

Abstract

The Chi River basin in northeastern Thailand is influenced by climatic conditions that affect rainfall and runoff during the rainy season, leading to flooding that affects communities in low-lying areas. Therefore, this basin is an area where flood management should be given considerable attention. The first objective was to identify depressions with potential for development as flood detention ponds by extracting them from the digital elevation model. The depressions were screened based on criteria including depth and non-overlap with existing roads and water bodies. Statistical analyses were conducted using suitability criteria, namely size, distance from rivers, and depth. The results revealed 22 potential areas of depression. Considering size, depression CD03 had the largest area, covering 140 km²; and a storage capacity of 1.13 km³. Another objective was to assess flood susceptibility in the study area using the Flood Susceptibility Index model and to produce a susceptibility map. This enables the research to serve as supporting information for decision-making in water resources management planning. Geoinformatics tools were integrated with the Frequency Ratio and Relative Frequency Ratio methods. Past flood inventory data from 2005–2020, comprising 68,780 flood points, were used; 70% were employed for analysis alongside nine factors: elevation, slope, aspect, profile and plan curvature, Topographic Wetness Index, drainage density, road density, and rainfall. The remaining 30% of the data were used for model validation. The results indicated that rainfall influenced the model; therefore, Model 2 was developed. The findings showed that 11% of the study area had high to very high flood susceptibility, and the model performance was classified as very good.