Assessment of Mun River Overbank and Diversion Strategies for Flood Mitigation in Ubon Ratchathani Province

Abstract

This study aimed to investigate flood conditions using the HEC-RAS 2D model, based on the 2019 flood event, which represented a 20-year return period. The simulation focused on overbank flooding from the Mun River in Ubon Ratchathani Province and evaluated the effectiveness of proposed flood diversion canal schemes. The Manning’s roughness coefficients used were 0.040–0.045 within the river channel and 0.07–0.12 for the floodplain. The model was calibrated and validated using data from the 2022 and 2019 flood events. Model performance was assessed using the coefficient of determination (R²) and root mean square error (RMSE), yielding R² = 0.978 and RMSE = 0.057 for calibration, and R² = 0.964 and RMSE = 0.14 for validation, indicating high model reliability. The simulation revealed a flood extent of 362.21 km², with a peak water surface elevation of 115.86 m MSL and a flood duration of 29 days. Three flood diversion scenarios were analyzed: (1) a canal diverting flow from the Chi River to downstream of Pak Mun Dam, (2) a canal diverting flow from the Mun River and Huai Khayung to downstream of Kaeng Saphue (bypassing Ubon Ratchathani urban area), and (3) a combined implementation of both canals. The results showed reductions in flood extent to 321.30, 328.12, and 270.60 km²; peak flood levels to 114.78, 114.65, and 113.44 m MSL; and flood durations to 26, 22, and 16 days, respectively. Scenario 3 was the most effective, reducing the overbank depth of the Mun River to 1.42 meters. This significantly mitigated flooding severity in low-lying areas, protected urban economic zones, and preserved main transportation routes.