Why did Derna’s dams break when Storm Daniel hit Libya?

There is widespread destruction across Libya’s east after Storm Daniel led to heavy flooding.

But the collapse of two dams in Derna, which gave out under pressure they could not handle, was the worst of it.

The dams caving under the pressure of water gathering behind them during the storm led to thousands of deaths in the port city alone.

So, why did the dams break, what happened to Derna, and what comes next?

Why did the dams break?

There were two major dams upstream from Derna that, for one, had not been maintained since 2002, according to Ahmed Madroud, the beleaguered city’s deputy mayor.

On the other hand, he told Al Jazeera, the dams were not very large, with the first dam only 70 metres (230 feet) tall.

Once one dam collapsed, the second one was facing a losing battle. Not only did it have to deal with heavy rains that were still pouring down in the storm, but it was also hit with a raging wall of water released with force from behind the other dam.

The multiplied force of the water was only strengthened due to the elevation difference between the first and second dams, and the stream took the second dam down on its way to Derna and ultimately, the sea.

Coming down the river, the water travelled approximately 12km (seven miles) from the top of the first dam before it reached the sea.

Experts estimate that 30 million cubic metres of water were released when the dams broke, equivalent to 12,000 Olympic-sized swimming pools.

What happened to Derna?

Derna, a city of roughly 100,000 people, was left completely defenceless after the dams broke.

Hichem Chkiouat, minister of civil aviation and member of the emergency committee of the eastern administration of Libya, said one-quarter of Derna was completely wiped out.

“I returned from Derna. It is very disastrous. Bodies are lying everywhere – in the sea, in the valleys, under the buildings. I am not exaggerating when I say 25 percent of the city has disappeared,” he told Reuters.

Madroud, the city’s deputy mayor, said on Tuesday that at least 3,000 people were dead in Derna alone, and bodies were still being pulled out of the water in large numbers, with fatalities likely approaching 5,000.

On Wednesday, the death toll was updated to 6,000 across eastern Libya.

Some of the bodies may have been washed out to sea along with the homes that were swept away by the flash floods. Entire neighbourhoods have now disappeared, according to witness testimonies and footage of the area.

Even multistorey apartment buildings that were not in the immediate vicinity of the river were significantly damaged and at least partially caved in due to the force of the water that broke the dams.

What comes next?

Thousands more people are still missing, and the death toll is expected to keep climbing.

Libyan authorities have called for foreign aid, which several nations are now providing, and more countries have pledged their help.

Authorities have deployed heavy machinery, including bulldozers, to assist with rescue operations in Derna and other cities, but the level of destruction has made reaching the flood-stricken challenging.

Rebuilding the largely dilapidated infrastructure destroyed in the floods is expected to be difficult and time-consuming.

The fact that Libya is governed by two rival governments, one in the west and one in the east, will only complicate matters further.

The country’s infrastructure had been neglected under the decades-long authoritarian rule of Muammar Gaddafi and fared no better since his overthrow and assassination in a NATO-backed uprising in 2011.

The two governments appear to want to cooperate on the emergency response to the flash floods, but divisions could still prove problematic.