On the morning of September 11, 2023, while most of the world remembered the horrific terrorist attacks of 2001, an even deadlier but lesser-known disaster was quietly unfolding thousands of kilometers away—in the North African nation of Libya. Just as Americans were lighting candles and remembering lost lives, the coastal city of Derna was being ripped apart in an instant by a catastrophe so vast that one out of every three of its residents may have perished.
The weapon wasn’t a bomb, but water—an unstoppable tidal surge unleashed not from the sea, but from the crumbling guts of Libya’s mountainous interior.
This is the story of how a thousand-year storm, two neglected dams, and decades of civil war and corruption collided to destroy a city… and how the tragedy might have been even worse because of the very dams meant to prevent it.
A City in the Crosshairs of Geography
Nestled in the far northeastern corner of Libya, Derna sits along the Mediterranean coast at the mouth of a seasonal river called the Wadi Derna. Behind the city, the Jebel Akhdar mountain range—Libya’s greenest, wettest, and most fertile region—funnels rainfall down narrow valleys like water through a firehose. These “wadis” are dry most of the year, but during storms, they can turn deadly in a matter of minutes.
With steep terrain, flash floods have long plagued Derna. The Germans noted it during World War II. Major floods were documented in 1942, 1956, 1959, and again in 1968. Each event more than hinted that something bigger might one day come.
In the 1970s, Libya’s government tried to act. But in hindsight, it may have planted the seeds of its own destruction.
The Dams That Were Meant to Save Derna
Between 1973 and 1977, the government under Muammar Gaddafi hired a Yugoslavian firm to construct two large dams upstream from Derna. The idea was simple: stop the floods before they reached the city. The larger of the two, Bou Mansour Dam, stood 75 meters high and could theoretically hold 22.5 million cubic meters of water. Below it sat the smaller Abu Mansour Dam, closer to Derna with a far more modest 1.5 million cubic meter capacity.
Both were built with a clay core and rock embankments—strong under normal conditions, but dangerously vulnerable if overtopped. The calculations at the time suggested these dams could withstand floods that would happen once in 1,000 or even 10,000 years.
But those numbers were catastrophically wrong.
And the third dam that was recommended further upstream to reduce strain on the others? It was never built.
Neglected, Forgotten, Doomed
Reports of cracks and structural weaknesses began surfacing as early as 1998. In 2003, a Swiss consulting firm warned that the flood volume estimates were grossly off, and that the dams were far too small for the potential load.
Despite the warnings, no maintenance was done after 2002.
Then came the Arab Spring.
Gaddafi’s regime fell in 2011, and Libya plunged into more than a decade of chaotic civil war. Derna changed hands repeatedly—from Libyan rebels to ISIS militants, then to al-Qaeda, and eventually to the Libyan National Army under warlord Khalifa Haftar. The city was under siege for five straight years. During that entire time, nobody—nobody—touched the dams.
Even after a ceasefire in 2020 brought relative peace, legal confusion and political division prevented any company from restarting work. Should they report to the UN-backed government in Tripoli? Or to Haftar’s GNS government in the east? Or to Haftar himself, the de facto ruler of Derna?
No one knew. So no one acted.
Enter Storm Daniel: The Perfect Disaster
In September 2023, an unusual meteorological phenomenon known as a medicane—essentially a Mediterranean hurricane—formed from Storm Daniel. It moved from the Balkans into Libya and slammed into the Jebel Akhdar with unprecedented rainfall.
At the Al-Bayda weather station, 414 mm of rain was recorded in just 24 hours—more than what usually falls in an entire year in eastern Libya.
Overnight, up to 100 million cubic meters of water—nearly five times more than the capacity of the Bou Mansour Dam—rushed into the Wadi Derna. There was no outlet, no emergency spillway, no backup dam. Just crumbling infrastructure, overtopping water, and silence.
The Collapse and the Wall of Death
At 12:30 a.m. on September 11th, 2023, the Bou Mansour Dam began to spill over.
By 2:00 a.m., its reservoir was overflowing by two meters.
By 2:40 a.m., the dam gave way—unleashing 30 million cubic meters of water down the valley like a liquefied freight train.
Twenty minutes later, it hit the Abu Mansour Dam, demolishing it instantly.
At 3:00 a.m., the sleeping city of Derna was smashed by a tsunami of water, not from the sea, but from the mountains behind it.
Entire neighborhoods were ripped from their foundations and dragged out into the Mediterranean. One survivor was rescued 11 nautical miles offshore the next day. All seven bridges over the Wadi Derna were destroyed. Five of the seven roads into the city were cut. One quarter of all buildings in Derna disappeared.
The confirmed death toll ranges between 11,000 to 24,000. Thousands more remain missing, and likely always will be.
Could the Dams Have Made It Worse?
A study published in the journal Science in 2025 modeled several scenarios and reached a shocking conclusion:
The disaster might have been less severe had the dams never existed at all.
Without the dams acting as temporary reservoirs, the rainfall would have passed more gradually through the valley. Instead, the presence of the dams allowed pressure to build up—until the collapse unleashed it all at once, supercharging the flood into a wall of devastation.
The dams meant to save Derna may have ensured its destruction.
A Legacy of Miscalculation and Corruption
This wasn’t just a natural disaster. It was a man-made one.
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Faulty dam design underestimated potential flood volumes.
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No maintenance occurred for more than 20 years.
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Civil war and political division prevented any repairs.
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Corruption may have embezzled money earmarked for dam maintenance.
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Confusing emergency messaging led residents to stay put rather than evacuate.
And in a dark irony, city officials had imposed a curfew just before the storm hit, ordering citizens to stay in their homes—right in the path of the coming deluge.
12 Officials Convicted—But Justice Feels Hollow
In 2024, twelve Libyan officials were arrested and convicted for their roles in the disaster. Their names were never publicly released. Sentences ranged from 9 to 27 years.
But many survivors feel that’s not enough.
They argue that those deaths weren’t just a result of mismanagement—they were the result of decades of negligence, conflict, and indifference.
Three Tragedies, One Date
September 11th is now etched with three separate international catastrophes:
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2001: The 9/11 terrorist attacks in the U.S.
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2012: The Benghazi embassy attack, just 250 km from Derna.
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2023: The Derna dam collapse, killing up to a third of the city.
Each tragedy shows how complex geopolitics, failed infrastructure, and poor planning can lead to massive loss of life. And how history tends to repeat itself—when no one listens to the warnings.
FAQ: Derna Dam Collapse
Q: How many people died in the Derna flood?
Estimates range from 11,000 to 24,000, with many more missing. Roughly a third of the city’s population may have perished.
Q: Were the dams ever repaired?
No. Despite contracts signed in 2007 and 2014, civil wars and political instability meant no meaningful maintenance was ever completed.
Q: What caused the dams to collapse?
A combination of record rainfall, overtopping, and erosion of the dam embankments. The failure was exacerbated by neglect and inadequate design specs from the 1970s.
Q: Could this happen again elsewhere?
Yes. Across the world, aging dams—especially in conflict zones—pose silent risks. Without maintenance, many are ticking time bombs.
Q: Is climate change partly to blame?
Likely yes. Warmer sea temperatures in the Mediterranean helped create the rare medicane, intensifying Storm Daniel’s rainfall.
Q: Did the government warn residents?
Poorly. Conflicting messages were issued—first ordering people to stay home, later calling for limited evacuations. Most residents stayed put, to fatal consequence.
