Dam safety |


Learning from the Libyan tragedy


An ICOLD workshop has assessed the Libyan dam failures which occurred during September 2023 in the aftermath of a catastrophic storm


References


An assessment of the failure of the Wadi Derna dams (Libya) and lessons for enhancing dam safety. Workshop on1st October 2024 during the ICOLD2024 Annual Meeting.


www.icold-cigb.org/ article/GB/news/ press_releases__news/ workshop--an-assessment-of- the-failure-of-the-wadi-derna- dams-libya-and-lessons-for- enhancing-dam-safety


www.nrc.no/ perspectives/2024/one-year- on-looking-back-at-dernas- flood-disaster


MARCUS WISHART IS WORLD BANK’S Lead Water Specialist for the Middle East and North Africa. Speaking at ICOLD’s Annual Meeting in New Delhi last year he said Libya isn’t typically the first place that springs to mind in terms of large dams. However, the country does have a relatively small portfolio concentrated on the north coast which plays an important role in ensuring water security, despite its arid conditions and natural scarcity of water. Wishart explained that a lot of these dams were constructed on highly variable ephemeral wadi systems that don’t have any flow for large parts of the year. They’re important not only in terms of flood management but for agricultural production, and are quite often positioned in such a way they support recharging of underlying aquifers.


Constructed in the 1970s, the Derna and Abu Mansour dams were built to control floods and protect the city of Derna, recharge aquifers, and provide water for the Fataya Agricultural project. Located around 1km upstream of Derna City, Derna dam was an embankment with a clay core that stood 40m high, with storage of 1.15Mm3


. It had a morning glory type of overflow spillway with a capacity of 350m3 /


sec. Abu Mansour Dam also goes by various different names and Wishart said this caused some confusion during the early stages following the failure. A 73m high embankment dam with a clay core it had a storage of 23.7Mm3


and catchment area of 476km2


Below: The Derna dam collapses in Libya were the catastrophic failures of two dams during September 2023, in the aftermath of Storm Daniel


/sec. . Located


around 11km upstream of Derna Dam it also had a morning glory overflow spillway and spillway capacity of 170m3


Storm Daniel Storm Daniel made landfall in Libya around 9 September


2023. Rainfall levels were well in excess of the long-term average, up to 200 times higher than expected during that period.


Wishart spoke about the impact of climate change and said heavy rainfall is up to 50 times more likely to occur compared with a 1.2°C cooler climate. So there are questions around the role of climate change in this disaster, as well as other considerations around original design parameters, particularly the idea there was a limited hydrological record to inform the initial design. Storm Daniel had significant far-reaching impacts not


just to do with the dam failures. After the event, a rapid damage and needs assessment looked at the extent of the damage. More than 250,000 people were affected by Storm Daniel with damages and losses equivalent to 3.6% of GDP and US$1.65billion. More than 4000 people died, 10,000 people were unaccounted for and 34,000 people displaced (although more recent estimates suggest the number of lives lost range from 5900 to 20,000, making this the second-deadliest dam failure in recorded history.) And over 7% of the country’s housing stock was destroyed or damaged with initial reconstruction estimated at US$1.8 billion.


Aftermath A collaborative assessment between ICOLD, UNESCO


and the World Bank took place in the aftermath of the tragedy. Wishart said it was difficult to source a lot of information as there were a number of conflicting reports in the public domain, including information provided by the original design firm. The country’s dam portfolio itself remains a little uncertain but there are 18 large dams in Libya, 14 of which are registered in ICOLD’s World Register of Dams. This was a useful starting point to understand some of the dam characteristics associated with the failure. Another noteworthy point was the highly variable


system these dams were constructed on. When looking at the overall portfolio, storage capacity is somewhere in the order of 380-390Mm3


and there are three dams that


22 | August 2025 | www.waterpowermagazine.com


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