More than 11,000 people have been killed and tens of thousands are missing following the catastrophic collapse of two dams in the eastern Libyan city of Derna. The dam collapse came after an extreme storm, Storm Daniel, slammed into the north African country. The Conversation Africa’s Moina Spooner asked water resources and engineering expert Nadhir Al-Ansari, who has researched the design and safety of dams, to provide insights into the disaster.
How does extreme weather affect the stability of dams?
Dams are usually built to withstand heavy rainfall or drought. The design and construction of a dam takes into consideration all possible effects. All factors, including the type of building materials, the design of the foundation and the stability of a dam, as well as expected floods and earthquakes and even military action, are taken into consideration when planning a dam.
Aside from how the dam is constructed, there should be safety provisions in place. For instance, in cases of storms, the engineers should release the water to ensure that a dam’s maximum carrying capacity is not exceeded.
In the Libyan case, I believe that the management of the dams was not good. The engineer responsible for the dam should have made sure the water did not exceed the dam’s upper carrying capacity. When he noticed that a huge volume of water was entering the reservoir he should have released large quantities of water to keep its level lower than the upper limit.
Research shows that the main causes of dam failure are foundation problems (40%), inadequate spillway (23%), poor construction (12%) and uneven settlement (10%). A site for a dam will not always be level because dams are built in mountain areas, but the designers must take that into consideration. The dam design must suit the topography. Among the rarer causes of dam failures are acts of war (3%), defective material (2%) and earthquakes (1%).
In Libya’s case, bad management appears to have been the cause of the dam’s collapse.
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