Warning Signs Present Ahead of Libya Dam Failures

Following the failure of two dams in Libya on September 10th, that resulted in significant damage and loss of life in the coastal city of Derna (see Sky News report), Value.Space was asked whether we could have detected issues with the dams beforehand. The answer is yes. Warning signs showing weakening of the dams were present before the heavy rainfall of the storm system Daniel caused the dams to fail.

Figure 1: Failed dams in Libya

• The dams that protected the city of Derna from potential floodwaters were constructed in the 1970s. Local experts and surveys had identified structural issues with the dams over the years, but the political and security situation in Libya prevented any action from being taken (for background see CarbonBrief Q&A).

• The Derna City dam (Al-Bilad dam) was located approximately 1 km south of the city centre, with a storage capacity of about 1.5 million cubic meters of water. The Abu Mansour dam was located about 13 km upstream along the Wadi Derna River and had a storage capacity of 22.5 million cubic meters of water.

Figure 2: Value.Space assessment of Derna City dam

• Value.Space’s satellite-based risk assessment of Derna City’s dam for a three-year period preceding the failure – from September 2020 to September 2023. Finds are marked on the dam.

• Find 01 - Deformation cluster on the dam slope where the direction of movement significantly differs from other movements of the dam, reaching up to 10 mm per year. Maximum cumulative deformation over the period was 30 mm.

• Finds 02 & 03 – Deformation clusters on the top of the dam where the direction of movement differs from other movements of the dam between 6.5 and 8.5 mm per year.

Figure 3: Value.Space assessment of Abu Mansour dam

• Value.Space’s satellite-based risk assessment of the Abu Mansour dam for a three-year period preceding the failure – from September 2020 to September 2023. Finds are marked on the dam.

• Finds 01, 02 & 04 – Deformation clusters on the top of the dam where the direction of movement differs from other movements of the dam between 7.5 or 12 mm per year. Maximum cumulative deformation over the period was up to 30 mm.

• Find 03 – Deformation cluster on the toe of the dam where the direction of movement differs from other movements of the dam, reaching up to 8 mm per year.

If the dams had undergone regular assessments by Value.Space, we would have issued a warning to the client to investigate the findings and take remedial action if necessary.

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