A Dam Shame: Engineer’s Warning Goes Unheeded and Eleven Thousand Die

Libya’s neglected dams collapse after Storm Daniel—2nd worst dam disaster ever.

The second-worst dam failure in history,[i] with over 11,300 people known dead, occurred on September 11, 2023, in Derna, Libya. In addition, tens of thousands are missing and 34,000[1] people were displaced when dams collapsed after torrential rains.

The tragedy underscores the importance of monitoring and performing maintenance of dams.

Most dams in existence today were built during the 1970s, a golden age of dam building, when the structures were going up at the rate of one thousand a year. The World Bank estimates that 19,000 large dams are over 50 years old. Many were built in countries, such as India, that can ill afford to maintain them. Many were built with earth and rocks, like in Libya.

Torrential rains from Storm Daniel, which had formed over Greece on September 4, swept into Libya and started to cause flooding in the coastal city of Derna on or around September 9, 2023. The worst was yet to come.

The Derna Wadi, a dry ravine behind the town, began filling up with water. Unlike previous annual rainfalls, this one was particularly severe, with an incredible 16 inches of rain falling in a 24-hour period. The area’s normal rainfall is about 10 inches annually. With most of the water flowing over dry, hard earth, the wadi accumulated some 20 to 30 million m³ of water. Trying to hold it back 9 miles (14 km) from Derna was the 74 m (240 ft) high Abou Monsour dam. Made of clay, rocks and dirt; neglected for decades; and damaged from previous storms, the dam was no match for a once-in-a-lifetime storm and it gave way. The water rushed down the wadi, encountering Derna’s last line of defense, the smaller earthen Derna dam on the edge of the city.

Both of the dams on the Derna Wadi were made of rocks, clay and dirt —not concrete. 

Not that there’s anything wrong with that, said William F. Marcuson III, former president of the American Society of Civil Engineers, to the New York Times. Earth and rock dams exist all over the world, and they are built correctly and maintained sufficiently.

That’s a big if. Libya had little money or interest in dam maintenance—for reasons soon to be explained.

Abdelwanees Ashoor, a hydraulics engineer in Libya, warned that the residents of Derna were in danger from the dams. After evaluating the volume of water from torrential rains, the capacity of the wadi, the data from the storms of October 1945 and November 1986 with geographic information system (GIS) software, Ashoor warned that the Wadi Derna basin “has a high potential for flood risk” and recommended the dams of Wadi Derna basin get their “periodic maintenance.”

Ashoor had sent his paper to colleagues in Tripoli, Libya’s capital.

Ashoor, reached by phone by the New York Times, was disconsolate. He had lost several members of his extended family in the flood.

“We’re living in shock,” he said. “We can’t absorb what’s happening to us. The state wasn’t interested in this. Instead, they guzzled money, practiced corruption and fought political squabbles.”

The first dam to collapse, the Abu Mansour. Image: Google Earth.

The Derna Dam on the edge of the city, the second dam to collapse. Image Google Earth.

The dams had been designed and built in the 1970s with the assistance of an engineering team from Yugoslavia. Abu Mansour, the large dam, was 74 meters high and held back 22.5 million cubic meters of water. The smaller dam, on the edge of Derna, was called al-Bilad or Derna Dam.

Libya is best known for two things: its dictator, Muammar Gaddafi, and oil. Gaddafi was deposed and assassinated in 2011, but the country’s high-quality sweet (low sulfur) crude oil remains much sought after. Libya has the ninth biggest oil reserves in the world and produces half a million barrels a day.^[ii] However, oil wealth has been spread evenly and since the demise of its authoritarian leader, the country has been wracked by civil strife that continues to this day.

Libya is effectively split between one faction in the East, controlled by the nationally recognized government in Tripoli, and factions in the West, composed of armed groups including Islamic militants. Ansar al-Sharia, a terrorist group, is considered responsible for the attack on the U.S. consulate in Benghazi in 2012. Though the Islamic State was largely defeated in 2016, other rebels still continue the fight.

Between East and West is the city of Derna, which has exchanged hands. It was last retaken by the East in 2018.

It’s no wonder dams were built to contain the seasonal torrents that occur once in a generation. And given the state of affairs of Libya, it is also no surprise that the government, split as it would be in a civil war, had more pressing existential matters to deal with than rain.

The dam was weakened in 1986 after a severe storm. More than 10 years earlier, cracks had been found in the dam, according to Libya’s general prosecutor. A 2021 government audit reported that no maintenance had been done on the dams despite more than $2 million allocated for that purpose between 2012 and 2013.

Wadi is an Arabic term for dry river valleys formed after eons of seasonal rains. They are a common feature in Northern Africa and the Middle East.

The Derna Wadi watershed. Image: Mheberger—Own work, CC BY-SA 4.0.

The Derna Wadi, one of the biggest of the wadis, runs primarily West to East, emptying into the Mediterranean where Derna lies. The shape of the land jutting into the sea on which the Derna is built suggests deposits of silt over the millennia.

Samy Magdy, Experts had Long Warned ‘Consequences Will be Disastrous’ if Dams in Libya Ignored,, PBS NewsHour, September 18, 2023.