Water structures' resilience to accelerated global warming impacts is attracting increased attention. Adaptation to unprecedented flash floods in semi-arid regions (e.g., Middle East and North Africa (MENA)) is becoming more challenging under the huge uncertainty of their frequency and intensity, lack of accurate hydrological studies, and water-resilient cities' absence in these wadi systems. Ten to twenty percent of Derna's population (similar to 90,000 people) were reported dead and missing along with more than 35,000 residents having been displaced (also, 737 completely collapsed, and 2859 partially collapsed houses) following two destruction waves after two dams' failures during unprecedented storm Daniel on the 11th of September 2023. In this study, we extensively investigated the causes and consequences of this significant main dam breach. We started by discussing the history of dams in the region and the Derna flash flood protection system design background. Then, we rebuilt the most probable scenarios and simulated the dam break analysis validated by a field survey. No matter how well-maintained the main dam was, the unprecedented Daniel storm flood highly exceeded its design capacity. Aside from the widely reported poor maintenance, our investigation of the overflow shafts of the two dams raised a potentially fatal design issue with the main dam. We concluded the most probable dynamics of the two dams' failure through two waves of destruction confirmed by diverse field observations. Ironically, the study concluded that a similar flood induced by the storm could leave much less damage in the case of the absence of any dams (i.e., far less maximum depth and velocity occurrence and fewer flooded areas). Therefore, it is imperative to review the design assumptions of comparable dams and upgrade or directly dismantle aging dams including those with reported low annual storage-to-design capacity ratios. Concurrently, reallocation of people and infrastructure from vulnerable low-lying regions, should be considered if achieving a complete and resilient system proves unattainable.
