The Study of the impact of water channel obstructions in the lower Mun River on flooding

Abstract

In 2022, Ubon Ratchathani Province experienced severe flooding that caused extensive damage to local communities. Local public opinion attributed the severity of this event to flow obstructions in the Mun River, particularly Kaeng Saphue and the Pak Mun Dam. These structures have raised concerns regarding their potential impacts on flood hydraulics. To explore this idea, this study will look at how these barriers affect flooding downstream using the HEC-RAS 2D hydrodynamic model. The simulation domain covers the river's reaches from the confluence of the Chi and Mun Rivers to the point where the Mun River flows into the Mekong River. The 2022 flood hydrograph was used to simulate flood extent and water levels under scenarios with and without the obstructions, including four different cases. Model calibration and validation were performed using data from 2019 and 2022, yielding high accuracy with R² values of 0.964 and 0.978, and RMSE values of 0.14 and 0.057, respectively. The study found that the water level at station M.7 was 116.50 m MSL in both the scenario with Kaeng Saphue and the Pak Mun Dam (OB.1) and the scenario without the Pak Mun Dam (OB.3), indicating no difference between these two cases. In contrast, removal of Kaeng Saphue (OB.2) reduced the water level to 116.15 m MSL, and removal of both obstructions (OB.4) further lowered it to 115.92 m MSL. These results indicate that Kaeng Saphue plays a significant role in raising water levels at station M.7, while the Pak Mun Dam has a secondary effect. When Kaeng Saphue is removed, the Pak Mun Dam becomes the primary obstruction contributing to upstream water level increases. This highlights the hydraulic influence of both natural and man-made obstructions in exacerbating flood impacts along the Mun River.