Catastrophic Dam-Break Flood Modeling and Risk Assessment: A Case Study of Yongning Reservoir, China

Dam-break floods pose severe threats to downstream settlements and infrastructure, especially in narrow mountainous river valleys. In this study, the potential consequences of a hypothetical failure of Yongning Reservoir were assessed using the one-dimensional MIKE 11 hydrodynamic model under partial-breach and full-breach scenarios. Model verification was conducted at Xuyong hydrological station, where the simulated results showed good agreement with observed data. The results indicate that the full-breach scenario produces significantly greater flood hazards, with peak discharge increasing from 23,865 m³/s to 108,940 m³/s. Flood depth, velocity, and inundation extent were also substantially higher, while flood-wave arrival time was shorter, reducing evacuation time. These findings provide a scientific basis for dam-break risk assessment and emergency planning.