Image source: Anadolu Agency
2 hours ago
The collapse of the two dams surrounding the city of Derna in northern Libya, as a result of Hurricane Daniel, raised many questions about the reasons that resulted in the unprecedented disaster in the country.
Libyan ambulance spokesman Osama Ali said, “The failure to maintain the two dams in Derna had a clear impact on the occurrence of floods.”
At least 5,000 people were killed in Derna, and about 10,000 people were missing, as a result of the floods.
The two dams, Abu Mansour Dam and Al-Bilad Dam, are located south of the city of Derna, with the second near the entrances to the city.
The height of the two dams was only about 40 meters before they turned into rubble.
Why were the two dams built?
The city of Derna has historically been exposed to a series of floods, including in 1941, 1959 and 1968. But the flood of 1959 had the greatest impact on the city.
Following this, studies in the 1960s suggested that levees should be built to protect the city from flooding.
Indeed, a Yugoslav company built the two dams in the 1970s, and the upper dam was called the country’s dam, with a storage capacity of 1.5 million cubic meters of water, while the lower dam, the Abu Mansour Dam, had a storage capacity of 22.5 million cubic meters.
The dams were built with a core of compressed clay with a surrounding shield of stone and rock.
Derna suffered floods in 1986, but dams managed the water to avoid causing serious damage to the city.
How did the collapse happen?
The Dams Administration in the Ministry of Water Resources of the Interim Government of Unity in Libya, headed by Abdul Hamid Al-Dabaiba, said that the flow of the amount of water stored in the Wadi Derna dams led to a weakening of the dams’ capacity and then their collapse.
The amount mentioned by the Ministry was estimated at about 23.5 million cubic metres.
The inability of the first dam to contain the flood led to the rapid flow of water towards the second dam, which led to its explosion as well.
Reports also said that the rainfall amounted to more than 200 mm, exceeding the design capacity of the structures.
Reports also indicated the need to study the possibility that this rainfall total could be attributed to climate change.
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Lack of maintenance and dilapidated infrastructure
Following the disaster, allegations emerged that maintenance of the two dams had been neglected for a long time. It appears that the structures of the two dams, which were built 50 years ago, were already dilapidated.
The lack of effective drainage systems and other protective infrastructure also made the surrounding areas more vulnerable to flooding.
In a research paper published last year, hydrologist Abdel Wanis A. said: R. Ashour from Omar Al-Mukhtar University in Libya said that the recurring floods in the valley pose a threat to Derna. He noted that five floods had occurred since 1942, and called for immediate steps to be taken to ensure regular maintenance of dams.
Ashour attributed the problems threatening the Wadi Derna Basin to several reasons, including “the occurrence of some damage to the existing hydraulic facilities, namely the two Wadi Derna dams, after the 1986 flood.”
He added that recurring floods from time to time have become a constant threat to the residents of the valley and the city of Derna.
Also, soil erosion in the basin due to flood waters is a major concern that negatively affects the vegetation cover, according to Ashour.
The research paper included a warning stating: “If a massive flood occurs, the result will be disastrous for the residents of the valley and the city.”
In addition, the long armed fighting that the country has experienced and the weakness of the government lead to further neglect and fragility of the infrastructure.
It should be noted that Derna is now not protected from the recurrence of a similar disaster, while the possibility of floods remains.
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2023-09-13 15:33:05
