Storm Daniel Breaks Two Dams Above Derna

On the night of September 10 to 11, 2023, torrential rain brought by Storm Daniel triggered the collapse of two embankment dams above the coastal city of Derna in northeastern Libya. The storm, which had previously caused severe flooding across Greece and the Balkans, made landfall near Benghazi and dropped torrential rain across the hills of eastern Libya. Upstream in the seasonal riverbed of the Wadi Derna, the reservoir behind the Abu Mansour Dam, about seventy-four meters tall and able to hold up to 22.5 million cubic meters of water, filled beyond its design capacity. When that barrier gave way, its impounded water surged down the valley and quickly overwhelmed the secondary Derna Dam, located just south of the urban center.

Built in the 1970s by the Yugoslav engineering firm Hidrotehnika-Hidroenergetika, the two clay-filled structures were designed for agricultural irrigation and downstream flood protection along a river valley with a documented history of major inundations. Both installations utilized bell-mouth spillways. Over subsequent decades, however, upkeep lagged. A study commissioned by the Libyan government more than a decade after a damaging storm in 1986 found cracks and fissures in the structures. A state audit in 2021 found that although more than two million dollars had been allocated for maintenance in 2012 and 2013, sustained work never materialized, despite repeated scientific warnings, including a 2022 university paper explicitly projecting catastrophic results in the event of major flooding.