Hydraulic simulation and risk categorization of flood events downstream of Namgang Dam

Abstract Flooding remains one of the most destructive natural disasters worldwide, presenting significant challenges to human lives, infrastructure, and ecosystems. This study evaluates future flood inundation risks in the downstream of the Namgang Dam in South Korea, employing advanced hydrological modeling to simulate extreme flood events. Using the Hydrological Engineering Center River Analysis System (HEC-RAS) model, inundation scenarios were analyzed for return periods of 20, 50, 100, and 200 years, based on design flood discharges derived through FFA using Gumbel’s distribution. Cross-sectional data collected from topographic surveys were integrated to simulate water surface profiles, flow, and inundation extents. The results underscore vulnerabilities in the downstream region, with inundation depths remaining within moderate‐ and low‐risk categories during the 100‐ and 200‐year flood events. Flood‐prone areas, particularly along riverbanks and low‐lying zones, were identified, highlighting the need for enhanced mitigation strategies. These include reinforcing embankments, revising land‐use policies, and implementing early warning systems. The study also reveals structural deficiencies in existing embankments where simulated water levels approached or exceeded the design capacity during extreme events. This research emphasizes the importance of adopting proactive flood risk management strategies amidst escalating climate change impacts, which exacerbate the frequency and intensity of hydrological events. By combining statistical analysis and hydraulic modeling, the methodology provides a replicable framework for flood risk assessments in other dam-controlled river systems. The findings contribute valuable insights for disaster preparedness, infrastructure planning, and policy formulation, offering actionable solutions to safeguard vulnerable communities and promote sustainable floodplain management.