The failure of Libya’s Wadi Derna dams and its role in the catastrophic aftermath

Storm Daniel, a Mediterranean hurricane system, caused widespread destruction in Libya this past week, bringing with it more than 400 mm of precipitation in areas that normally receive 1.5 mm for the whole month of September.

Probably the most determinant reason behind the dramatic aftermath that left entire neighborhoods in the city of Derna completely wiped out, as well as thousands of people dead or missing, was the failure of the Wadi Derna dams.

The Wadi Derna dams were two dams upstream of the city along the homonymous river valley and located at distances of one and twelve kilometers away from Derna.

As for their capacities, it has been reported that the upper dam was able to store 1.5 million cubic meters of water and had a height of 45 meters, while the lower one was 75 meters high and could hold back 18 million cubic meters of water. However, it is worth noting that these height dimensions seem exaggerated, as Dave Petley also notes at The Landslide Blog.

The city of Derna has experienced flooding incidents several times in the past, from the 1940s to the 1960s, and the construction of the dams was deemed necessary for the protection of the city in the future.

They were two earth dams constructed from 1973 to 1977 by a Yugoslav construction company that is now based in Serbia, and reports have been made, by Derna Deputy Mayor Ahmed Madroud, about maintenance neglection since 2002, largely due to political reasons.

A paper published in late 2022 by civil engineers Abdelwanees A. R Ashoor, of the University of Omar Al-Mukhtar also supported the dams’ lack of maintenance, quoting  "the current situation in the Derna valley basin requires officials to take immediate measures, carrying out regular maintenance of the existing dams, because in the event of a huge flood, the result will be disastrous for the residents of the valley and the city".

The first speculations include overtopping of the upper dam, which led to the lower one being overwhelmed by the volume of water and subsequently getting washed away too.

A video of the moment that the water mass entered the city of Derna shows no large amount of water flowing in the stream prior to the event, which raises questions about the operation of the dam’s floodgates.

However, only speculations are currently in place, as the exact reasons behind the events have not yet been determined.