Dam Failures in Derna, Libya 25

[SSCon]

https://eos.org/thelandslideblog/the-failed-dams-in-wadi-derna-in-libya

 

[3DDave]

There is zero indication that the recent event wasn't more severe than past.

 

[LittleInch]

I've had a flick through GE history of these two dams and can't find any photos at any time of the year that actually show ANY water in either of the dams (!) to the extent that trees are growing in the bottom of the dam.

The overflows are both two concrete glory hole type affairs which isn't uncommon.

But it could be that these dams have never been effectively tested before now and maybe the central clay core dried out after 50 years in the desert heat and dryness?? so as soon as they were ever needed they failed?

This is the lower one, but larger higher dam is similar. The height of the higher up dam seems to be about 45m, with the lower one more like 25m.

The size of these dams though seems relatively small ( about 2.5 million cubic metres from a quick GE assessment. compared t the destruction wrought, but I guess a wall of water on a low lying coastal plain town would be very bad. Some of the destruction though could be secondary rain flows once the dams then selves went.


Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TugboatEng]

Some of the destruction though could be secondary rain flows once the dams then selves went.

Certainly. In the 1941 flooding event the natural flows were strong enough to wash away German tanks. In the 1959 event, hundreds of people were killed without the torrent caused by a dam failure. I don't see much about 1968.

 

[1503-44]

Oh it is true in Spain. This year there have been record rainfalls. What used to be commonly 10 to 20 liters/m2-h have seen increases to 25-40+ liters/m2-h. And they have occurred in a matter of an hour rather than over 3 to 6 -12 hours.

This is the latest of many such events this year.

https://www.euronews.com/2023/09/04/record-rainfall-in-spain-leads-to-deaths-and-travel-chaos

The Libya storm dumped record levels of rain on Greece just before arriving in Libya. The 300mm number is from the Greek Met Agency reports.

4 days ago

https://phys.org/news/2023-09-greece-rainfall-mediterranean-weather-dangerous.html

754mm in 18 h = 42 liters/m2-h

Greece & Turkey

https://www.itv.com/news/2023-09-07...severe-flooding-in-greece-turkey-and-bulgaria

Norway

https://www.theguardian.com/world/2...orway-with-heaviest-rain-in-25-years-forecast

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[1503-44]

https://www.aljazeera.com/news/2023/9/13/mapping-libya-flood-damage

https://www.ibtimes.co.uk/how-dams-derna-caved-flooded-city-171

Both say about 30M, one says cubic yards, the other says 12000 olympic size swimming pools (50m x 25m x 2m) 12000 x 2500 =30Mm3
Almost the same.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[TugboatEng]

Yes, California had a historic amount of rain this year as well. It was not record, though. That happened in 1862.

https://youtu.be/ugh33NI_vsM?si=ySaraUy5EqInTSqu

 

[1503-44]

2nd thought. Actually the reports do not give the size of the dams, but estimate the water volume flowing into the city. Perhaps the dams were 3M m3, water volume 10 X dam volume?
Yeah, that's a fail.

California ... not next to a 27.5°C ocean. Some areas are drier, others wetter.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[LittleInch]

There no way those dams held that much water, but total water flow might have been that close when you take into account the water volume which fell in the area and fed into the wadi.

Either way, they were not designed for that sort of rain fall and had no major secondary spillway. But they would have needed a dozen dams to hold back the rainfall that was experienced there without the water escaping the wadi banks in the middle of the city.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

That little wadi drains 575km2
Putting houses in the downstream path was ... a disaster all by itself.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[TugboatEng]

One of the articles posted said "climate threat" in the headline. That was a break from always seeing "climate change" as the blame. This city was in a very threatened area.

 

[1503-44]

The storm is being called a Medicane, a new type of storm in the region can form over high temp Mediterranean Sea waters.

CNN

The two dams that burst on Monday were built around half a century ago, between 1973 and 1977, by a Yugoslav construction company. The Derna dam is 75 meters (246 feet) high with a storage capacity of 18 million cubic meters (4.76 billion gallons). The second dam, Mansour, is 45 meters (148 feet) high with a capacity of 1.5 million cubic meters (396 million gallons).
Those dams haven’t undergone maintenance since 2002, the city’s deputy mayor Ahmed Madroud told Al Jazeera.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[TugboatEng]

Medicane sounds a lot like fire tornado. Another new term to describe an existing phenomenon. Firestorms used to exist. Now they're called fire tornadoes I guess.

 

[dik]

@pham... is that ever a neat link...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

@Tug... I think it was the mayor of Lahaina that referred to their fire as a fire hurricane... first time I had heard that expression... maybe a thing of the future to look out for?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Brian Malone]

Human behavior puts populations at risk. The two dams added to the wadi for flood control by definition allows people in the area to live in and develop in locations that traditionally would have been avoided. The possible insufficiency of the flood control structures would not be recognized since it is hard to create flood conditions on demand to test the flood mitigation to ensure it can perform as expected. These events are less nature diasters than human diasters. Human activity put humans in a flood channel. The constant talk of increasing storm intensity is wearing on me - the human population has increased and our cities and homes are increasingly expanding into areas that formerly would have been open, wild land that would have absorbed the action of the storm with little impact on humans and any storm intensity would have been largely ignored. Certainly human actions have changed weather patterns but the micro examination of every storm and weather event with the proclamation of evidence of climate change raises my inner skeptic.

 

[dik]

...or maybe conditions can change, too.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[LittleInch]

Those figures come from the original article and just don't make sense when you look at the actual dams and dimensions on GE. The higher dam is not 10 times larger. More like 1.8 and 1.5 million?

Any way, clearly inadequate compared to the amount of water which fell. But 50 years ago I doubt anyone could foresee that level of rain.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[dik]

The upstream topography may have an impact...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[SWComposites]

https://www.nytimes.com/2023/09/16/world/middleeast/libya-dams-warnings.html

 

[TugboatEng]

Any way, clearly inadequate compared to the amount of water which fell. But 50 years ago I doubt anyone could foresee that level of rain.

Has anyone confirmed that the dam spilled over?