Dam Failures in Derna, Libya 25

[SSCon]

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

 

[dik]

It looks like the western world is doing it by themselves...

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

-Dik

 

[3DDave]

Not only is the Western world working hard to destroy itself, it extends that effort to kill everyone else.

Derna is listed as the most fundamentalist Islamic city in Libya. I fail to understand how anyone in the West would presume to tell them where and how to live.

 

[TugboatEng]

Is aerospace not the most fundamentally Western industry?

 

[1503-44]

"We could build infrastructure, too."

Does not comply with the military industrial complex core list of products. Infrastructure construction shall be limited to military airports with associated aircraft hangers, clubhouses, swimming pools, tennis courts, fences and guard houses.

Apparently the UN does do those dam studies you talk about. I have been conversing with a guy that says it is what he does.

--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]

AZPete, I am leaning towards believing that the dams were sized appropriately for their time using the available data of the day. Total capacity seem to be around 18Mm3.

--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]

I've seen the data for 1900 to 2021. There was no reason to expect that a storm of this kind would ever affect Libya. It was probably a 10 to 30x average outlier. No 5-day total rainfall in Libya ever exceeded 16mm. This storm apparently hit with 100mm in a few hours. Maybe considerably higher due to local topographical conditions. A true black swan.

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

 

[dik]

With climate change, there will likely be a lot more of these events on the horizon.

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

-Dik

 

[LittleInch]

That's all sounding about right.

Even if they took 20 or 25mm of rain over a 5 day period to size the dams, getting hit with at least 10 times that volume of water, plus increased run off rates would simply overwhelm any storm holding dams. The fact the dams clearly failed as well simply added to the initial surge of water, but if not then it would have been almost as bad I think.

So a bit like those dams in the NE of the US which failed a couple of years ago - anyone / anywhere with dams which could fail and cascade really needs to be doing some revision and emergency planning to deal with a x2, x5 or x10 design rainfall event.

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

 

[1503-44]

I wrote a couple hundred words, but the text disappeared when I submitted. That's the short version.

Here is the rainfall data summary I found.

See if you draw the same conclusion.

Yearly average is around 25mm, max ever 55mm.
5day rainfall total is available apx 8mm, highest ever 16mm.

10mm on a 157km2 basin at full 100% runoff, not very likely, but still, is 1,57 Mm3.
25mm is apx 4,0 Mm3
100mm is 15.7 Mm3 50% over max ever recorded yearly rainfall.
Assume the 55mm yr total is 1 in 100yr event, that's the data right there.
55mm 8.63Mm3, worst yearly max ever.
50mm is a 50year yearly rainfall total event, we saw 2 in that range in 100 yrs of records.
40mm is a 20-25yr frequency.
25mm is a yearly frequency.
Those only became apparent during/after the 80's.
In the 50s, those didn't even look possible.
Keep in mind those are yearly totals. Not convertible to dam capacity, which might, I don't know exactly, only be 25% of those numbers.
55mm, 100 yr total rainfall 8.6Mm3 might represent something like 4 x an actual dam design capacity and they have 2 x that.

1 year totals are very much different than 1 day totals. It's totally unreasonable to expect to get 2 x a worst case year's rainfall in a day, never mind a minimum of 4x that in a few hours.
Yet the dams could hold that much.


I don't really believe the downtrend lines. It's flat. Only the computer thinks it's a downtrend.
2022 and 2023 are missing, so that will only kick it up, not down.

 

[1503-44]

The possible maintenance issue is a separate problem. I only wanted to know if the designers blew the capacity number. I think, certainly not. No such storms were ever recorded in the history of the region and I believe this storm was not even predictable as an extreme black swan. Its rainfall was far greater than 3 σ.

A storm like that has never been seen in the area before. You can call it climate change, or not, but it is a new thing one way or another and I think ... the answers have changed. This is a wake up call.

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

 

[TugboatEng]

There is some new debate over how quickly canyons form. They may not be formed by slow erosion but by massive singular flood events.

https://www.livescience.com/8312-canyons-form-quickly-gusher-suggests.html

What happened in Derna might be a first for the region but it seems to occur regularly throughout Earth's geological history. Maybe the steep walls of the Grand Canyon are a sign it was formed by a massive flood and not gradually as once thought.

 

[AZPete]

Its rainfall was far greater than 3 σ.

If all storms over all regions persist in breaking 3σ threshold, then maybe a new day is here. Taking one instance in isolation is not, per se, a marker of "change". Nothing magical about 3σ. Assigning causality to it is way off as well. Geologically, we don't have squat for time study/frequency of climatic phenomenon by which to assure construction with complete resistance to natural events and still be "economically sensible".

 

[LittleInch]

Well the English channel (26 miles at its thinnest point) was apparently formed due to release of a huge sea of melt water to break the land bridge that was existing between what is now the UK and the European mainland.

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

 

[1503-44]

Yes, it is true. Black swans are more common than we realize, basically because they don't happen often enough to accurately gage their frequency, hence probabilities in the long tails are not well understood and slight errors in estimated probability drastically affect freq & v/v. But they do happen, so we must all be very careful with the big consequence events.

The Colombia River was apparently formed by a natural dam break and the Great Lakes and Mississippi were the result of the massive glacier melt over a relatively recent and short time.

All we can say about Libya is that these events aren't in the written history. Geologic evidence is that North Afric-Saharah was considerably wetter, surely not much hotter, than present and probably not all that long ago. 10,000 to 100,000 ago. Salt water clam population of the Black Sea is nonexistant in the fossil records until being flooded by the Med. The Opening of the Bosphorus and Black Sea formation may have been responsible for the Great (Noah's) Flood in prehistoric but very recent recent time, as it was thought to have displaced many early settlements of the time. Actually only 7500 years before present.

https://www.smithsonianmag.com/science-nature/evidence-for-a-flood-102813115/

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

 

[AZPete]

Who were the big breakthrough idea people in history? People like Archimedes, Gutenberg, Curie, Einstein, Fermi, Watt, Da Vinci, etc.? List them by the hundreds, thousands, perhaps. What fraction of the population do they represent, then and cumulatively? Small number. Yet, it's those little specs in time that are big, outsized motivators of progress.

In any sample, they practically are not discoverable. Over time and space, they are "frequent enough".

Science and risk management ought to be a fairly low-key and amicable discovery process, very pragmatic and tempered. Unfortunately, it gets raided by table-topplers intent upon something or other but not relative truth. No accusations here, just a side comment.

 

[dik]

AZP... you missed Tesla, but I glad you got Watt... and not for the steam engine, but for the governor...

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

-Dik

 

[1503-44]

AZ structural and civil env engineers are already doing exactly what you don't have time for. As discussed further above. Perhaps mechanical engineering has not yet been severely affected by rainfall? Maybe your design temperatures have had some impact somewhere, which might have gone unnoticed, if you don't follow the climate records of the area.

Yes this just one storm, but of a type and magnitude never seen in the historic records of this region before. It is very likely that, after updating the region's design conditions data base, a significant change will be incorporated that will impact both existing and future infrastructure in this region.

There have been at least some impacts to mechanical engineering. The "Texas Big Freeze" effectively changed the design conditions for cold weather operation of electric generators and gas pipeline capacities when ERCOT required modifications be made to ensure continued operability of all Ercot connected facilities. Gas production and pipeline companies have installed heaters and numerous operational changes in guaranteeing electrical supply is maintained to gas production facilities, rather than being taken offline as before those changes were made. That also was "just one storm".
Undoubtedly, being a mechanical engineer, you can more easily find other examples than I which have affected MEs already. I don't follow that very closely.

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

 

[AZPete]

The wadi looks to be something that only nature could have designed, and it likely did not involve chipping away with a mallet and chisel. Doubtless, there were phenomenal amounts of water and sediment coursing through the landscape over time.

When you set up permanent camp in a regional low, don't blame mankind for nature's propensity to throw a gutter ball once in a millennium or ten.

 

[1503-44]

Well yes. In fact we are finding out that philosophy applies to just about everywhere, for one type of disaster or another and it may lead to not being able to keep on building things disregarding the maximum power that mother nature can throw at us. In fact we may not even know what that power level is.

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

 

[dik]

I'm not so sure... design for a blizzard in the Atacama or Sahara desert doesn't make much sense...

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

-Dik