Post-disaster review and mitigation strategies for the “2023·9” dam-break flood in Derna, Libya

This study conducts a retrospective analysis of the flood processes caused by the failure of two dams in Libya to provide insights for dam safety management in China. By integrating satellite precipitation, remote sensing imagery, and measured breach cross-sections—with forecasting-operation, hydrodynamic and breach models, the entire flood process was reproduced. The results indicate that the upstream Al-Mansour Dam reached full capacity around 2:00 on September 11, with an inflow of 2 634.4 m³/s. The downstream Bilad Reservoir also reached full storage around 2: 15 due to intermediate inflows,consistent with official reports. The Al-Mansour Dam failed at approximately 2:30, with breach outflow peaking at 24 476.4 m³/s by 03:00. Around 2:40, the Bilad Dam was breached under the combined effect of intermediate flow and the floodwave from the upstream dam failure, reaching a peak discharge of 21 488.5 m³/s at 3:15. The dam-break floodwave reached Derna about 0.3 hours later, causing extensive overbank flooding, with a simulated maximum inundation area of approximately 2.55 km²—closely matching remote sensing observations. This reconstruction reveals key mechanisms of cascading dam failures under extreme precipitation, offering critical references for enhancing reservoir and dam safety management in China.