"They knew."

When hydrologist Abdul Wanis Ashour began researching the system of dams protecting the eastern Libya port town of Derna 17 years ago, the peril facing residents was already no secret, he said.

"When I gathered the data, I found a number of problems in the Derna Valley: in the cracks present in the dams, the amount of rainfall and repeated floods," he said. "I found also a number of reports warning of a disaster taking place in the Derna Valley basin if the dams were not maintained."