Hydrodynamic Analysis of Landslide Dam Breach Formation and Outburst Flood Propagation in the Sunkoshi River Basin, Nepal

A dam breach is an uncommon but profoundly destructive event that transpires when a dam collapses, releasing accumulated water downstream and leading to extensive damage. This study focuses on the Jure landslide dam, located in the Sindhupalchowk district, Nepal. The region is characterized by complex river channels and steep terrains, which are significantly influenced by flood dynamics. This study aims to establish a compressive numerical simulation of a two-dimensional dam breach unsteady flow hydraulic model to simulate the dam breach process and downstream flood propagation. The study analyzes the dynamics of the Jure landslide dam outburst flood, emphasizing the flood characteristics, inundation, and velocity hazards in the mitigation of flood impacts. The results reveal that the peak discharge of the Jure landside dam was 5336.7 m3/s, while it decreased to 1181.4 m3/s when traveling 35 km. The flood depth obtained by 2D (HEC-RAS) downstream of the dam rages between 0.0334 and 55.9 m, while the corresponding estimated peak flow velocity of simulated breaches was 21.46 m/s, demonstrating extreme hydraulic force conditions, capable of catastrophe. The proposed hydraulic simulations reveal significant variations in overflow dynamics across different terrain types, with narrower sections exhibiting faster flood progression and greater water depths. The findings underscore the necessity of accounting for terrain heterogeneity in future flood risk assessments. This work offers valuable insights into the emergency management of landslide dams in similar regions.