It had been clear for years that the dams protecting Derna, on Libya’s Mediterranean coast, were in danger of giving way.
Torrential rains were not new. Decade after decade, they had pounded the area, washing away the soil that helped soak up water as it ran down from the dry hills above town.
Climate change had also changed the land, making it drier, harder and increasingly shorn of vegetation, less able to absorb the water before it pooled up dangerously behind the dams.
Then, there were the decades of neglect by officials — who knew the dams needed repairs — in a country so torn by years of civil war that it still has two opposing governments: one in the west and another in the east, where Derna lies.
Academics had warned that it would not require a storm of biblical proportions to overwhelm the dams.
The residents of Derna are “extremely vulnerable to flood risk,” wrote Abdelwanees Ashoor, a hydraulic engineer at Omar Al-Mukhtar University in Libya, in a paper he published in 2022.
The kind of storms that had hit the area in recent decades — he cited a damaging flood in 1959 — could bring down the dams and inundate Derna, he warned, calling the situation “dangerous.”
This past week, those predictions grimly proved to be true, when enormous flooding from a powerful storm broke through both dams and swept parts of the city into the sea. Thousands are dead and many more missing, according to the authorities. According to the International Organization for Migration, over 34,000 people were displaced by the catastrophe.
Reached by phone, Dr. Ashoor said he had lost several members of his extended family to the flooding this past week, adding that the government had ignored years of warnings — including his own paper.
“We’re living in shock. We can’t absorb what’s happening to us,” Dr. Ashoor said. “The state wasn’t interested in this. Instead, they guzzled money, practiced corruption and fought political squabbles.”
The dams had been built by engineers who had underestimated the amount of rain expected in the region, he argued. Making matters worse, the terrain had undergone a process of desertification, making it less porous and capable of absorbing runoff. Beyond that, local officials say the dams had barely been maintained since their construction in the late 1970s.
Dr. Ashoor said he had sent his paper to academic colleagues in the nation’s capital, Tripoli, and a senior dam expert in the United States said his conclusions appeared to be solid.
“He nailed it,” said Michael W. West, a retired principal at the engineering firm Wiss, Janney, Elstner. “His main point is that the hydrologic design of those dams was inadequate, and they couldn’t handle the large-magnitude storms.”
“It’s probably devastating to know you were right, plus the personal tragedy on top of that,” Mr. West added. “I can’t imagine how he’s feeling.”
Libya, an oil-rich nation on the shores of the Mediterranean, has been worn down by years of civil war and government misrule. Climate change only added to the strain, helping to turn the once-fertile terrain arid and desolate.
The two dams that towered over the city had been built with the help of engineers from the former Yugoslavia, according to experts. The larger one, known as Abu Mansour, stood 74 meters high and could hold up to 22.5 million cubic meters of water. The smaller one, al-Bilad, or simply Derna dam, was built on the city’s outskirts.
During the long, autocratic reign of Col. Muammar el-Qaddafi, floods came and went, but the dams stood. In 1986, a major storm convulsed the region, damaging the dams and shearing soil from the ground. The structures were damaged, Dr. Ashoor said, but again they held.
Despite the stresses, repairs were minimal. In 1998, the Libyan government commissioned a study that revealed cracks and fissures in the dams, said Attorney General Sadiq al-Soor.
Nearly 10 years later, a Turkish company was finally contracted to repair the dams, the prosecutor added. But the government dragged its feet in paying, and the project got underway only in 2010, Mr. al-Soor told reporters on Friday.
Just four months later, in 2011, Libyans marched against Colonel el-Qaddafi’s 42-year grip on power, inspired by the uprisings that had toppled Arab autocrats in Tunisia and Egypt. When he threatened to annihilate the opposition, NATO intervened and bombed his forces, with the United States a backbone of the operation. Colonel el-Qaddafi was ousted from Tripoli that August.
In the tumult, work on the dam ceased, the prosecutor said.
He pledged that the authorities would take “firm measures” against anyone deemed responsible for failing to properly maintain the two dams. “This is extremely important for protecting the rights of the victims and to determine who was responsible — if there was neglect or dereliction of duty,” said Mr. al-Soor.
He said that the authorities had appointed prosecutors from different parts of Libya to investigate what caused the dams to collapse, inspect houses and determine whether maintenance measures could have prevented the disaster.
More than a decade after Colonel el-Qaddafi’s chaotic ouster, the country remains split between an internationally recognized government in the west and one under Khalifa Hifter, a military commander who controls the east, including Derna.
Derna was a key battleground during the country’s civil war, which saw the city fall under the control of Islamist militias. After a protracted siege, forces loyal to Mr. Hifter declared victory in 2018, although skirmishes continued for several months.
All the while, the neglect of the dams continued.
According to a 2021 report by Libyan state auditors in the west of the country, more than $2.3 million allocated for maintaining the two dams was simply never used. They called it a case of government negligence.
And as recently as last week, less than two days before the dam burst, a Libyan nonprofit, Roya, wrote on Facebook that the dam could fill to bursting during the powerful storm that was sweeping across the Mediterranean.
“We ask the residents of the valley to be very careful,” the group said.
Even as the waters swelled, some officials, far away in Tripoli, said just after midnight on Monday that the dams were in “good condition” and that there was “no cause for concern about collapse.” They added, however, that the storm had affected their ability to contact those charged with monitoring one of the dams.
Very soon after, well before dawn, the rising waters appear to have overwhelmed the dams — first the larger Abu Mansour dam, then the second, smaller one downstream, which was obliterated in a matter of “moments,” Dr. Ashoor said.
The rampaging tide wiped out large chunks of the city, shattering roads and bridges, washing away cars, and smashing apartment buildings, witnesses said
Whole families were killed, officials say, drowned or trapped under rubble. Others were dragged out to sea.
William F. Marcuson III, a former president of the American Society of Civil Engineers, said that these dams — which were made with clay and rock — were common around the world.
“There’s nothing wrong with that approach, if it is done correctly,” he said. But, he added, the dams must be designed for the maximum rainstorms likely, and be constructed under careful inspection, so that no corners are cut.
The dams included concrete spillways that are supposed to function much like an overflow drain in an ordinary bathtub: If the water rises too high, it goes into the spillway, down underground pipes, and is discharged below the dam.
But if the spillway is not built to a sufficient size or the pipes are too narrow for the strength of the storm, the water continues to rise.
When it rises over the top of the dam — called “overtopping” — the dam itself begins to erode. As that happens, the embankment, which supports the dam, is gradually eaten away until the entire structure fails and the water flows freely.
If the upstream dam failed first, a wall of water may have wiped out the lower dam frighteningly quickly.
With no more obstacles in its path, the water tore through the countryside, fanning out over dozens of kilometers. The main force of the raging torrent slid into the natural funnel of the Derna river basin, where residents say they were issued confusing, sometimes contradictory, orders on whether to evacuate.
In a televised speech on Thursday, Aguila Saleh, the speaker of the Parliament in the nation’s east, sought to bat away accusations that the scale of the devastation was rooted in government mismanagement and neglect.
“Don’t say, ‘If only we’d done this, if only we’d done that,’” Mr. Saleh said. “What took place in our country was an incomparable natural disaster.”
Dr. Ashoor acknowledged that the flood was prompted by a giant storm rarely seen in the country. But he believes the authorities could have done far more to minimize the risk.
“Political strife, two governments, all of the wars we’ve seen since 2011, terrorism, all the problems we’ve faced,” Dr. Ashoor said. “All of this gathered together to lead to this deteriorating disaster, this calamity we’re living through. May God ease this crisis.”