Why was the damage to Derna so catastrophic?

Greater than 5,000 persons are identified to have died and hundreds extra are lacking after devastating floods swept by the Libyan coastal metropolis of Derna.

Total neighborhoods disappeared into the ocean when an enormous tsunami-like torrent of water swept by town.

Total households have been swept away, based on a Libyan journalist who spoke to survivors within the metropolis and described the scenario as “past catastrophic.”

BBC Verification and the BBC Visible Journalism workforce have analyzed a number of the the explanation why floods induced such catastrophic harm in Derna.

File rainfall

The waters introduced by Storm Daniel arrived in Libya on Sunday.

The storm, a Mediterranean cyclone generally known as Medicane, dumped greater than 400mm of rain on elements of the northeastern coast over a 24-hour interval.

That is an uncommon deluge of water for a area that usually sees round 1.5mm of rain all through the complete month of September.

The Nationwide Meteorological Heart in Libya mentioned that rainfall set a brand new file.

Map showing heavy rainfall in northern Libya and highlighting Derna and Benghazi

Map exhibiting heavy rainfall in northern Libya and highlighting Derna and Benghazi

It’s too early to confidently attribute the depth of this storm to rising world temperatures.

Nonetheless, local weather change is believed to extend the frequency of probably the most highly effective medicine.

Professor Liz Stevens, an knowledgeable in local weather danger and resilience on the College of Studying, says scientists are assured that local weather change is resulting in elevated rainfall related to such storms.

The 2 dams have been overwhelmed

The Wadi Derna River extends from the inside mountains of Libya, by town of Derna to the Mediterranean Sea.

It’s dry for many of the yr, however unusually heavy rains have flooded two essential dams and destroyed a number of bridges.

Metropolis residents, who have been ordered by native authorities to remain of their properties, reported that they heard a robust explosion earlier than water flooded town.

“The dams would have held the water again initially, and their failure would possible launch all of the water without delay.

“Particles suspended within the floodwaters would have elevated the damaging drive,” says Professor Stevens.

Specialists who spoke to BBC Confirm say it’s too early to know whether or not the heavy rainfall was merely an excessive amount of for the dams to deal with, or whether or not the situation of the constructions additionally performed a task.

Primarily based on their observations, the dams are possible made from dumped and compacted soil or rock, which isn’t as sturdy as concrete.

“These dams are susceptible to overtopping (when water exceeds the capability of the dam), and whereas concrete dams can face up to overtopping, rock dams usually can not,” says Professor Dragan Savic, a professor on the College of Exeter and an knowledgeable in hydraulic engineering.

It seems that the higher dam collapsed first, based on structural engineer Andrew Barr.

He says the water might have then flowed down the rocky river valley towards the decrease dam earlier than submerging it, resulting in sudden and disastrous flooding of town trapped between the mountains and the ocean.

As rescue efforts proceed within the metropolis, Libyan journalist Jawhar Ali, who spoke to survivors within the metropolis, informed the BBC: “Folks hear the cries of kids underground, and so they have no idea easy methods to attain them.”

“Folks use shovels to dig our bodies out of the bottom, and so they use their fingers,” Ali mentioned. “All of them say it’s like doomsday.”

A drawing showing the burst dams and the destruction of four bridges

A drawing exhibiting the burst dams and the destruction of 4 bridges

The car is covered in mud and rubble

The automotive is roofed in mud and rubble

Games seen in the affected store

Video games seen within the affected retailer

Produced by Chris Clayton, Mike Hills, Paul Sargeant, Toral Ahmadzadeh, Cady Wardle, Gerry Fletcher, Philippa Silverio and Erwan Revolt. Further reporting by Mark Pointing, Peter Muay and Jake Horton

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