Yes, a cascade failure of two compacted earth dams. Both built in the 1970s.

A "wadi" is also called an arroyo in Spanish and a dry wash in Western US English.

During WWII, a large group of German troops set up camp in a wadi (perhaps this one?). It rained. That benefited the British.

From this, I decided that a wadi/arroyo/dry wash was a poor choice for long-term encampment. Which appears to be what just happened in Libya.



spsalso

Appears to be very limited high ground in the affected zones of Derna so no where for the people to flee. The water flow scoured everything in its path.

https://www.nytimes.com/2023/09/12/world/middleeas...

Dams without effective spillways is not acceptable practice.

Do we know that the dam spilled over or did the foundation fail?

Spsalso, what country? Alt. orollo, or... a barranco (revine). Arroyo is the stream in my usage, although depends what country and dilect. Spanish is not widely consistent across regions and can be very different between countries.

But yes, a wadi is a very steep, if not vertical revine. Extremely dangerous (obviously) during rainstorms as they are usually in bare rick with minimal vegetation. All water runs off and at very high speed and there is no escape route up the sides.

Comments left on the blog say...

Quote:

There is also a pre-failure video from March 2023. Note that the shaft spillway and its surroundings appear very clean. This seems to indicate that an overtopping of the dam is unlikely to be the cause of the failure.

So may have been a blow out below, or tunneling erosion.

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

"arroyo", as used in the US. And, quite likely, Mexico.

FWIW, I just missed going to Arroyo High School, down in Los Angeles.


spsalso

"Wadi" is a term used in Arabic countries, which just means a river or stream which is dry most of the time. Can have steep sides, but not necessarily.

That vertical structure is not a "shaft spillway". It is an inlet or control tower. It would allow some water to escape, but miniscule in relation to a properly designed emergency spillway.

The design/integrity of the dam structures may have had little to do with this disaster. The drainage basin of Wadi Derna is significant and exits above Derna through a narrow gap. Storm Daniel delivered tropical rains to the entire region and overwhelmed the infrastructure or any that might have ever been planned. Once the dams let go, they flooded the city which was already inundated with a foot of rain where normal amounts are measured in fractions of millimeters.

The circumstances were far more grave than the flooding of B.C./Washington several years ago where action on disaster planning could have mitigated much some of the damage.


Wikipedia


Relief exagerated


Relief exagerated


reliefweb.int

Quote (Sym P.le)

Storm Daniel delivered tropical rains to the entire region and overwhelmed the infrastructure or any that might have ever been planned. Once the dams let go, they flooded the city which was already inundated with a foot of rain where normal amounts are measured in fractions of millimeters.

It's my understanding that this region typically gets all of its annual rain within a few days. I don't think this storm was extraordinary.

I have no idea about that region's typical climate. But topography tells a story about it's past. Those canyons aren't there by accident, they are there because millions of years of erosion by rain have put them there. Flooding might not be common, but when it occurs it is dramatic. Not a whole lot different in parts of the US canyonlands.

According to Google (yes, I know, not a 100% reliable source!), the average annual rainfall for Derna is 330 mm, while Storm Daniel delivered something like 100 mm in 3 days. I suspect this event was "extraordinary" from the perspective of the local population, but probably well and truly within the range of what the dams SHOULD have been designed to accommodate.

Fifty or so years ago, designing a dam for 100-year or 1,000-year events might have been normal, but even then, there should have been an emergency spillway to pass bigger flood events - e.g. for a major rainfall event when the dam is already full. From the aerial imagery, I can't see any sign of an emergency spillway on either dam. Once you get overtopping of an earth dam wall ...

The upstream dam had a significantly bigger capacity than the downstream dam on the city's perimeter; the flow of water from the failed upstream dam would have overwhelmed the downstream dam very quickly.

http://julianh72.blogspot.com

Anyone have access to this journal?

https://bfemu.journals.ekb.eg/article_199421.html

This storm was an extreme event, not typical of the season.

24h rainfall rates were measured at up to 440mm in Greece, shorter term rates were estimated at up to 300 mm/h, showing the receipt of very high volumes during very short time frames, some storm events lasting only 1 hour during which many areas received 40 to 77% of their total expected yearly amount. This is also not the usual rainy period in the region, more normally during March to May, and Nov-Dec. This time is normally still hot and dry. Summer does not end until 21 Sept.

Current Med temp measured at 27.5°C 83F off Libya. Med is at all time max recorded temps. That same ole +1.5°C keeps popping up everywhere, even in my latest highest monthly average max kitchen temperature. 5yrs ago it never passed 25-26.



Not restricted to Med.
NOAA latest precip amount intensities and return periods are here,
https://hdsc.nws.noaa.gov/pfds/
check them against your old local building codes, they may be 34% or more higher for storm prone areas. Check Charleston SC 10 yr. Now Miami at +46%





Offshore Gulf of Mex platform design criteria was revised back in in 2010 to consider frequent CAT 5 storms.

Don't look up.

--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, how is any of that pertinent to the Wadi Derna flooding due to Storm Daniel? 100 mm in 3 days may be extreme in that part of the world, but any dam should have considered rainfall of that magnitude, if not much greater. The design, if there was one, was totally inadequate, and the worst part was the lack of emergency spillways. There likely would have been significant flooding over the spillways, but not as catastrophic as what occurred. The stated purpose of the dams was flood control for the city, and they spectacularly failed their mission.

Actually I don't think we know if the dams spilled over or damage was caused by some other defect, or what event magnitude and frequency it was designed for. This was the same storm that came into Libya from Greece.

I'm just saying that storm events are significantly increasing in magnitude and, if you are involved with drainage and storm resistance design, a check of your building code requirements against the new data might be prudent.

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

The question is, can all contingencies be accommodated at any cost. Historic rainfall over broad drainage basins may be one contingency to many. Then we can get into the specifics of who is correct about the rainfall totals. The relief agency map suggests 100 - 300 mm (4" to 1') of rain over the entire drainage basin, and regardless of time period, that surge would have to be metered by the two dam structures above Derna.

I would not venture out beneath any North American dam structure that is over topping with greater volumes yet to be realized. These things are not crash tested.

Quote (1503-44)

I'm just saying that storm events are significantly increasing in magnitude

This isn't true at all. The dams were built in response to severe flooding events in 1941, 1959, and 1968. There is zero indication that the recent event was more severe than past.

https://www.aa.com.tr/en/environment/floods-in-lib...

I'm with 1503-44 on this...it's my last hope for a purpose of this forum...how many of us will design an earthen dam in our career? Probably not a lot. But a lot of us do design structures that have to deal with rain load in other ways, and using this disaster as an opportunity to reflect on our practices and assumptions in tangentially related fields is the greatest benefit of this forum as I see it. After all, I doubt the NTSB checks in here for ideas.

We base a lot of our engineering to resist environmental factors on statistical models. That's great, but we have to be open minded about the base data and accept that it may not be as reliable as we think. This is especially true when an upward trend in the model output presents itself, suggesting that we lack a sufficient data set to forecast some of these events. If we run the model every 5 years and expand the data set and the result is not converging, we need to consider other sources of data and observation to inform our design assumptions.

The ASCE 7 hazard tool presents rain fall rates based on the Precipitation Frequency Data Server linked to above, and the newer editions point to those for structural engineers to design roof structures that have the potential for retaining water. Unfortunately, plumbing codes seem to be lagging behind and are creating a mismatch in expectations. I haven't had it happen yet, but I've come close to "code compliant" plumbing designs resulting in excessive retention on the roof now that I'm designing for more stringent requirements.

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

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.

Quote (LittleInch)

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.

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-rainfal...

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

Greece & Turkey
https://www.itv.com/news/2023-09-07/death-toll-ris...

Norway
https://www.theguardian.com/world/2023/aug/08/stor...

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

https://www.aljazeera.com/news/2023/9/13/mapping-l...
https://www.ibtimes.co.uk/how-dams-derna-caved-flo...
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."

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

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."

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.

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."

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.

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."

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.

@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

@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

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.

...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

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.

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

https://www.nytimes.com/2023/09/16/world/middleeas...

Quote (LittleInch)

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?

The numbers: Estimation of the surface runoff depth of Wadi Derna Basin (sebhau.edu.ly)

Quote (Abstract)

... As a result of the model applied, the annual runoff volume for forty years during 1960–2000 in the study area was estimated by 138.51 Mm3. Furthermore, a volume flood has been estimated, based on the flood of October 1945 and late November 1986. Those events called for average precipitation of 145 and 64.14mm respectively. The rainfall of 1945 produced a volume flood of 53.36 Mm3, which represents 40 % of annual runoff volume, while the flood of November 1986 was 14.8 Mm3, which is in good agreement with the recorded flood in the basin.

100 mm over 575 km² (Wikipedia, Wadi Derna) is 57.5 Mm³. That approximates the 1945 flood volume. This rain event was 100 - 300 mm (reliefweb.int) over that same area which could be double that volume of water or more. The dam capacities are in the order of 20 and 1.5 Mm³ (various sources). Interestingly, the study included a single event of 145 mm but the abstract does not mention capacity issues for the dams. I'm curious about the rainfall rate and runoff/discharge rates used. I suspect a 100 Mm³ event could easily overwhelm the structures, even if they were in good condition.

I also suspect that a single surge from a dam failure would have an outsized impact relative to a steady heavy flow. The war time event would have been spared that peak. I still question whether a quadruple or quintuple capacity system is ever in the cards. I suppose an infrastructure comparison would be the lone Japanese town of Fudai (Youtube) that built an outsized Tsunami break wall.

SymP, it would indeed be interesting to see fainfall rates, duration, storm travel speed and basin coverage. Unfortunately we will probably be left guessing.
Have you been able to download that first link? I can't seem to do it. Site keeps jumping back to the original icon. Can't even keep it's login page open.

Medicane
It's a new term to describe known phenomenon (reaching hurricane like size, similar high water temp cause and effects) occurring in regions where they haven't been seen at the same magnitude before.

Brian, no hydrotest is required. These effects can be predicted by a simple Excel open channel flow calculation, or more elaborate CFD study for a few thousand bucks. We don't have to fill dams with water and blow them up. The potential dangers these dams presented are easily recognisable and, no doubt, would have been recognised assuming that even a minimal amount of study was conducted. Such extreme risk would have been identified and the project halted. But it was built. Why? Could we assume that at the time these were built, the risk was classified as minimal. With hindsight of this disaster, how it could have presented a minimal risk might seem unfathomable today, but that could easily have been the case.

Was the design of these dams perfectly adequate for the design conditions identified back in the day? Why would we assume otherwise, noting that at least so far, there is no evidence to the contrary and we have no reason to believe that they were poorly designed. We expect engineers, even way back then, to be able to build dams. So let's consider what might have happened since then that made these dams such a high risk project that eventually killed 11,000 people.

We are immediately inclined towards thinking, well there must have been a problem with the physical design or construction of the dam, or, think, Of course it happened, it wasn't maintained for years. Or, they let people move into that high risk area. While it is true that all those factors could have contributed to increasing risk, there is at least one more important factor we should consider. A factor that is probably more easily recognised in projects designed for a specific production capacity, such as chemical plants, refineries, power generators and pipelines, among others. When you run at more than design capacity, things start going wrong fast. For dams and reservoirs, we usually think of maximum capacity in terms of water level, but not necessarily about how that was determined. And when we do think about maximum rainfall and drainage area, we tend to think that those numbers are sufficiently high, relatively permanent constants that will give us safe results, rather than considering them as highly dynamic variables. Even if we did, would we consider them to have a potential variation range of 2 or 3 times what is assumed as "a basically maximum constant design value". Probably not. We would have to build a refinery with twice our initially planned capacity. We would never do that. It would never be an economically viable plan.

So, what this disaster suggests is that rainfall rates, i.e. climate data was once probably adequate for the safe design of these dams, and they survived for 50 some years. People got killed by living in the wrong place, but that perspective may be based on hindsight alone. Before today's rainfall data, the dams could have been safe, but today we know they are not. Sure, more people are living in high risk areas up the consequences, but those people had nothing to do with the high rainfall rates. High casualties are a symptom, not the root cause. What this disaster apparently proves is that the design conditions for these dams have changed. Nobody would build them as they were based on this weeks rainfalls.

What can we do to solve these specific types of problems (dams, reservoirs, flood controls)? Each and every dam and potential flood zone (maybe in the whole world, you be the judge) needs to be revaluated using the new data. If I lived downstream of one, you can bet I surely would have done it already. The full monty, CFD and all. In some cases it may be feasible to build bigger and better, but where high variability is present, tear down may be the only solution. I predict a great future for hydrologists.

We can be skeptical of reasoning behind this, but it seems obvious to me that changing design conditions are forcing us to consider higher winds, higher tides, more fires, more and higher flood controls, desertification, invasive species, glaciers and disappearing water resources , Great Salt Lake and Colorado River diminishing flow and higher offshore platform deck levels. All those are facts and we are already taking those measures. Being skeptical does not prevent disaster. Even the most ardent former skeptics are being forced to admit to it and are now saying, Oh just let it happen. Its too expensive to do anything about it, but what that fails to recognize is that it may also be too expensive not to do anything about it. You can be skeptical if you want, but [spoiler alert] the skeptic frog in a warming pot of water does not survive. Doing nothing also has its costs.

Is it true that medicanes will become prevalent in the Med, with their very few hour rainfall rates totalling 77% of the previous yearly accumulations for these cities. Only time will tell, but it looks like that's where we're going.

--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 your analysis is very complete and knowledgeable and I certainly recognize humans are affecting the very world we live, yet does not change my belief the impact of weather events to humans is not necessarily because the events are more intense - it is because either humans have moved into risk prone locations or our population has increased in such locations - often because humans use technology for mitigation or financial methods such as insurance to encourage utilization of areas with potential for loss. The parable of a frog in a warming pot is analogous to human behavior not that of a frog in a natural setting because a frog floating in warming liquid would leave before the temperature is dangerous. If given no path of leaving the frog would exhibit distressed behavior. Frogs do not live in pots - only humans do.

Estimation of the surface runoff depth of Wadi Derna Basin (sebhau.edu.ly)

The PDF is attached below

• https://files.engineering.com/getfile.aspx?folder=de0080d7-41a3-4d3f-9c2c-7

Reader's response to an article in today's Times (UK, London version):

Its not just the locals, the media need a hard navel gaze too. We used to shrug and blame "gods" - now media shrug and blame climate change and "worst floods on record". Few have asked why the Wadi is what it is, why (and by who) the dams were built on it, how these dams ended the city's flood problem, which was causing huge losses of life and property. These include the 1941 flood, which caused great losses to the German army, the 1956 flood, the catastrophic flood of 1959, the 1968 flood, and the 1986 flood, which, although large, the dams prevented damage to the city. So the city grew, oblivious to the old threat. The dams have not been maintained for over 20 years since Libya is a failed state (wonder why), and then another storm arrived, as science predicted. Not man's fault - bend the knee to the climate change god and carry on BAU.

Politicians like to panic, they need activity. It is their substitute for achievement.

LPS to that reader.

Brian, thanks. I try to make some sense of these things.

Hpwever I do think your reasoning confuses mortality data with rain gages. Saying that mortality data depends solely on how many people live in risk prone areas is certainly true, but it ignores why the area is classed as high risk. Take earthquakes. No association with climate change that I know of, so its pretty safe to assume your theory is 100% correct there. If I did a regression of earthquake mortality and climate data, I.e. rainfall rates and durations, size of storms etc., there is no way I would expect to see any connection whatsoever to any of those data points. But if I did the same analysis on drunk driving and traffic deaths, that connection would be very obvious. Now, why don't you do a regression analysis of flood deaths and rainfall intensity in a flood risk region and tell us what that regression study shows. Sure its important to realize that regression analysis is not proof of cause and effect, but it also does not prove that it isn't a cause and effect. What it does is add strongly to the evidence when a possible connection is seen.

In the end, as I say, we are increasing the design conditions anyway. The insurance companies demand that to minimize their payout risk. Doesn't matter if we see a connection or not. They see it and costs of increased design robustness are already on us one way or another. Nobody will insure an offshore platform with a 20ft lower deck height. Have you tried to get flood insurance lately?

Multiple Variable regression analysis
https://corporatefinanceinstitute.com/resources/da...
http://www.ieomsociety.org/detroit2020/papers/516....


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

Quote (The parable of a frog in a warming pot is analogous to human behavior not that of a frog in a natural setting because a frog floating in warming liquid would leave before the temperature is dangerous.)

The frog 'parable' is myth..

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

-Dik

Debunked. But you get the picture, right?

Puds post, Reader comment is the reason behind the high number of deaths, but it misses the probable root cause entirely. It most likely hits the action plan square on.

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

Lack of maintenance wasn't the probable root cause?

maybe a huge increase in rainfall that was never anticipated or planned for?

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

-Dik

The dams were built for the rainfall! The valley has a long history of deadly floods and the dams stopped that for some time. Nobody has indicated that the dams spilled over. As others have noted, the basins are dry most of the year. It seems the dams broke while filling and not due to being overfull.

There is no precise information on exactly when or why the dams did not hold.

What has been reported is
30Mm3 of water passed through the city in an apparently very short time.
Water depth reached 7m in the city.

LittleInch has estimated the dam retention volume as roughly 2Mm3.
The dams are now gone.

If the dams held, that would mean that there was a 32Mm2 of rain water shed from the basin, 2M of which would still be behind the dam. They did not hold, so we assume shed rainfall was 30M.

A water shed 15 X dam capacity tells me that, if the dams broke or held isn't important, as in either case the city would be whipped out by either 30M, or 32Mm3 of water. That's an inadequate capacity issue. If these dams were designed properly 50yrs ago, we can suppose that a 2Mm3 rainfall runoff was the expected runoff, including whatever safety factor was used in determining runoff volume and adequate dam retention design capacity. Today we see runoff is now 30M, 15X what apparently was considered adequate 50yrs ago. Why is that? 50yrs ago they knew that it would be dangerous to build dams there if they got the capacity wrong; they knew the wadi had severely flooded several times already. They must have wanted to get it right used the best available rainfall data at the time.

Today we have only two possible answers as to why dam retention capacity is inadequate.

1) Engineers 50 years ago had no idea what they were doing and underestimated runoff, using a value of only 2/30 = 7% of what they should have. They were complete idiots? Or was the data totally wrong and they made no attempt to verify it by looking at trace levels of previous floods.

2) Engineers 50yrs ago did a proper job with their rainfall/runoff calculations, but for some reason runoff expectations today need to be 15X higher than the 2Mm3 they calculated 50yrs ago. "The answers have changed."



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

A Turkish firm was contracted in 2007 to carry out maintainence on the two dams and build another dam in between. The firm, Arsel Construction Company Ltd., said on its website that it completed its work in November 2012. It didn’t respond to an email seeking further comment.

Another tragedy is the lack of failure modes analysis, surveillance and monitoring, and emergency planning. There are plenty of dams around the world that have vulnerabilities. But the potential failure modes need to be recognized, continuously monitored, and planned for. Every dam whose failure could kill people (high hazard) needs to have an emergency action plan kept up-to-date and regularly exercised. This way when conditions indicate that a PFM could be triggered, people can be clearly warned to get out of harms way. For all of this to happen there needs to be a stable government to regulate and enforce a dam safety program. Here in the US, dams are regulated by the states and the federal government, but we are not perfect. Alabama started regulating their dams only this year, and with some dams there can be political pressure to keep unsafe dams operating to maintain waterfront property values.

Regardless of the magnitude of the rainfall event that was used to design the dams, they should have been designed to handle that magnitude of event when they were already full. Even if the dams were designed solely to manage "rare" flood events and the dams are normally empty, there is a very real possibility of two or more rain events in short succession, such that the dams are still full when a subsequent major rain event strikes.

The only way to do this without overtopping the dam crest is some sort of emergency spillway, which I cannot see on the aerial images of either dam.

http://julianh72.blogspot.com

Per LittleInch and the Google Earth image, both dams had overflow systems in place. As was demonstrated at the Oroville dam, a spillway can be insufficient even given a relatively minor amount of spill. It is very difficult to provide a spillway on earthen structures as even a slight over-capacity of the spillway will immediately begin eroding the dirt from around and under the spillway.

concur about the difficulty... the Oroville dam failed partially because the concrete spillway was poor... concrete spillways are often used with earthfill dams and generally function as they should.

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

-Dik

If they had an overtopping spillway, it most certainly would not have been designed for 15X and we could add that material to whatever went through the city. They certainly would have failed.

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

Without accurate data on the rainfall from 1941, 1956, 1958, or 1968 I am not convinced the 'medicane' event is a new weather event. I don't think it is known what input/output criteria was used for the dam designs and if they were designed with sufficient flow and storage capacity for an event such as those reported in 1941, 1956 . . . I have looked at the Google Earth images of the Derna wadi dams and they are retention flow dams with bellmouth overflow structures, so they would be damaged/ destroyed with overtopping. Maybe the dams were underdesigned and for the last 50 years the rainfall has not reached levels such as the level that occurred in the flood years - is enough information available to decide?

Brian
Underdesign of a dam above the city is a certain death trap. Nobody would build it.
I do not intend to convince you of anything. You must draw your own conclusions.

HERE IS WHAT YOU ASKED FOR
The EuMedClim Database: Yearly Climate Data (1901–2014)
of 1 km Resolution Grids for Europe and the Mediterranean Basin
http://gentree.data.inra.fr/climate
https://www.frontiersin.org/articles/10.3389/fevo....

Finding the data from 2014 to now should be the easy part.

CLICK ON THIS LINK TO DOWNLOAD FULL DATA SET
FILE SIZE:573.6 GB I ran out of space on my micro drive at 2.22GB and had to cancel.
Talk about overtopping! I'll have to buy a TB drive just for this one file.
https://nextcloud.inrae.fr/s/AwPX8PjzRkgDiS8

--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 thanks I will give a look at the data to see if there is specific enough info for Derna and its region in 1941 1956, and 1958.

I don't agree with your assumption an undersized dam would not be built upstream of a population center. Dams are built to the funding allocated and the directives of the entity with the most political power at the time of construction. There are plenty of examples of inadequate dams being built and failing. Even those that seem to be at the vanguard of technology can make mistakes. The inadequate earthen hillside emergency spillway of the Oroville Dam is a prime example:

https://damfailures.org/case-study/oroville-dam-ca...

In hindsight people were surprised the dam's emergency spillway was flowing down the earthen hillside and threatening to destabilize the dam. The engineers who designed Oroville dam were well respected.

we are trying to equate western principles to a third world country.

I might add during the Libyan conflict the military forces were told to keep the hell away from those dams and the post conflict teams to have nothing to do with them. And that's from UK sappers.

There has been very little support since ghaddifi left power. Basically all pretence of first world engineering stopped after lochobie.

Amen, Alistair. Was just about to post something similar. All this babbling on about the dams as if they were in a western country with a functioning government is just useless. Go read the NYTimes article I posted above; it was well known that the dams were in poor condition.

I'm not talking about the condition of the dams. Condition is not relevant to rainfall rates having changed, or not.

The dams were designed well before Lochobie.

I also don't see Oroville as having any relation. Dams fail for many reasons. Oroville failure did not involve excessive rainfall. The spillway failed due to a number of causes. Miscalculation of rainfall rates and storage volumes was not mentioned in that investigation, There is far more information on that subject right here on ET
https://www.eng-tips.com/search.cfm?q=Oroville&...



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

Lockerbie.

"In February 2017, heavy rainfall damaged Oroville Dam's main and emergency spillways, prompting the evacuation of more than 180,000 people living downstream along the Feather River and the relocation of a fish hatchery." https://en.wikipedia.org/wiki/Oroville_Dam_crisis

The main spillway was unable to handle the amount overflow from the heavy rain.

Regardless of implementation problems, the presence of two overflow spillways was insufficient at Oroville and blaming the lack for this disaster boils down to blaming the residents for their poverty (and for not living elsewhere) when the first world chose not to spend their wealth on their own dam which was close to a similar failure from a less intense increase over normal rainfall.

There is a bit of politics and ideology seeping through here... To be honest I have little knowledge about the climate of the region, though as I did point out that basic topology observation and understanding of a desert canyon environment does point towards extreme long tail events regardless of other made made climate change factors. On the other side of things, the warmth of the extreme Mediterranean this year cannot be ignored.

We are engineers, in our profession we should be agnostic towards the politics of the climate change politics. In my home country Australia, we introduced an explicit factor in our wind code for cyclonic regions to account for the changing climate. Right now that factor is 1.0. But it was deliberately introduced acknowledging the currently quantifying increased risk.

...a slight issue. Engineers should never be agnostic about anything. True agnosticism stipulates that the 'truth' will never be revealed.

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

-Dik

Dam bursts happen everywhere and usually for the same reasons:

https://en.wikipedia.org/wiki/Lawn_Lake_Dam

--- Best regards, Morten Andersen

https://www.reuters.com/graphics/LIBYA-STORM/EXPLA...



Can we stop arguing about whether the weather set new rainfall records.
It says it did here. 414mm/24h
Unfortunately 24h is often the best available resolution and we don't get hard evidence of maximum rainfall intensities over shorter durations.










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

Quote (1503-44)

Underdesign of a dam above the city is a certain death trap. Nobody would build it.

My point about Oroville Dam is not about miscalculation of rainfall - it is about design mistakes can be made. The emergency spillway per the original 1968 design was inadequate to prevent erosion due to the very waterflow it was intended to carry and the design was done and reviewed by many capable minds. And the dam was built with an underdesigned critical feature upstream of major areas of population. My statement was and is: mistakes can be made.

Original emergency spillway:
https://www.ussdams.org/wp-content/uploads/2017/02...

New improved emergency spillway:
https://water.ca.gov/Programs/State-Water-Project/...

The dam operators had to make very difficult decisions when the limitations of the emergency spillway became apparent and the realization was made the design was inadequate from day one but it had never been used before. The belief was it would never be needed - the main spillway and powerhouse channels would always suffice.

It is apparent the rebuilt e-spillway addresses the issue of hillside protection as the original should have.

Hi Brian. Yes I understood your point was to explain there were other causes at Oroville. What I want to do is emphasise that I take the root cause of failure of the Derna dams as an extreme weather event that caused an overload on the dam. Whether the dams actually failed because of pressure from too high a water level, tunnel erosion at the dams base, a geologic fault, spillway overflow-erosion-destruction event, a construction defect, or maintenance issues is not important in the context of whatever broke the camels back was initiated by the extreme weather event.

What I am getting at is ...

If it didn't rain 414mm in 24 hours, none of this would have happened at all. In that context, was not the dam's failure sequence initiated by the extreme weather event? In that sense, weather would be the root cause of this failure.

If the dams were in perfect condition, so much water running through them could have overloaded the spillway, increased the base pressure too high, or tunnel eroded under the dams base, or manifested in failure from any number of reasons, but it was the weather that initiated the path to eventual failure. Given the record rainfalls in the area, I contend weather could have been enough to cause severe overload on any one or more of the dams systems resulting in total failure. Weather started it all.

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

Got it! A lot of water did fall in a short time! No rain, no flood, no failure.

I've gone to the NOAA Precipitation rate data site above where I have collected the data tables on rainfall intensities for 5 US cities on the East Coast, areas subject to high intensity storms. Galveston, Tx, New Orleans, Orlando, Fl, Charleston SC, and NYC. I have Normalized all time-intensity values to the 24h rainfall intensity figures, creating factors for each time-intensity value for all cities. The normalised factors are remarkably similar.

If I assume that these intensities are valid for medicane storms, yeah, it might be a stretch, but I did it anyway, I maybe can get an idea of rainfall-time intensities of medicanes.

What it looks like is that in all those cities time intensities, and using the Derna value for 24h intensity of 414mm, then applying them to the 575km2 area of Derna drainage basin, they all result in roughly 30M m3 of rainfall in being generated in only a 5 minute storm duration.

I need to take runoff into consideration and find the potential volume of water reaching the dams for various concentration and storm duration times, but what it looks like so far is that medicane rainfalls are very capable of overwhelming any dam in its path, maybe within a few hours, IF the dams storage volumes and spillways were designed using the lighter rainfall intensities of the region based on previous rainfall records. 100mm rain on this basin generates a volume of 50Mm3. Accumulated rainfall is seen to possibly have reached 300mm+. That would surely have whipped these dams out regardless of any typical spillway protecting them. If so, there looks to be little likelihood that any dam in this region can survive such extreme events. If these become common occurrences, there's a lot of trouble ahead.

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

LittleInch, I found another report on retention volumes, this one at 18 and 1.5Mm3



And this one with 22 and 1.5M.
https://www.scmp.com/news/world/africa/article/323...

And this guy says 18M looks high.
https://eos.org/thelandslideblog/further-informati...

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

Those figures are a bit better - I did a recalc on the top dam and now reckon its about 10-15 Mm3. But the dam wall is no way 75m.

not sure if that's what it was supposed to be as its in a wadi that is about 75 deep, but the dam itself is more like 30m max.

Either way, it was never going to hold back the deluge which arrived over the space of a few hours from its hinterland. you would have needed more than 10 of those similar ones all the way back.

They were simply a disaster waiting to happen and no maintenance was going to stop that volume of water.

The latest GE images have been updated and if you look at the damage on the river bank it shows that the wall of water was about 20m high coming out of the gorge by the lower dam. Everything under about 12m elevation looks to have been enundatede

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

Dam specs, from the builder.

Type of dam: Embankment dam with clay fill
Dam height: 75 m
Crest length: 300 m
Foundation width: 104 m
Embankment: 735.000 m3
Storage capacity: 18.000.000 m3

Type of dam: Embankment dam with clay fill
Dam height: 45 m
Crest length: 130 m
Embankment: 104.000 m3
Storage capacity: 1.500.000 m3

Well ... the one thing they all agree on is the top dam is 1.5
Confusing.

SSCon, Super thanks for the post.
I'll go with that.

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

African Precipitation records by Yr up to 2021
By year, hopefully not 1 653GB file.
https://cds.climate.copernicus.eu/cdsapp#!/dataset...

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

I've a feeling that when they say dam height they include the 15 to 20m that they dug into the wadi floor to get some anchorage / down to the impervious layer for the inner clay plug to prevent water leaking und it and de-stabilising it.

So a bit like this.

There is no way those heights are height from bottom of the upstream side of the wadi / normal ground level to top of dam. However dam volumes seem about rightish based on the GE images and measurements.

So about 15 to 20 Mm3 for the upstream / higher up / southernmost dam and then about 1.5 to 2 M m3 for the downstream just above the city / lower down / northern one.

This is a picture of the lower one and shows with the scouring that the wall of water must have been truly biblical in its full flow at some 20m high torrent of water. You can see the trench they dug originally to seal the core of the dam.

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

In case it was missed. I could find every other article from that edition of the journal but the relevant one. Maybe someone else's google fu will be better.

https://www.hidrotehnika.rs/en/libya/wadi-derna/

Quote (Mathematical Model of Dam Break: Applied Study of Derna Dam (2002))

The dam break is a very complicated problem and it can’t be foreseen exactly. Many researchers have studied the problem of dam break by predicting the behavior and the propagation of a flood wave using different approximations. In the present research, the study of dam break was performed using a mathematical modeling as a tool to predict and simulate the dam break problem. Two major mathematical models were employed namely BREACH and FLDWAV for predicting such failure parameters as well as simulating the flow routing after dam break. Derna dam (northern east coast of Libya) was taken as a case study of an earthen dam. So, collected information about Dema city and Derna dam were included in the current work. Piping failure was considered the most predictable one for Dema dam. For the current study it was shown that dam break cause a potential danger towards Dema City, since flooding occurs in the city for all hypothetical scenarios. It was recommended to predict the routing of the flow after failure due to lowering the retained water surface elevation in the reservoir and due to the use of levees and increasing walls heights in the city area.

Thanks both. I'm just gonna use those retention values and not worry any more. Seems to have converged, on 18 and 1.5M. If I need to get dam height, I'll put that much water in the lake valley profile and calculate a level at the dam location. But I might not get into it that far. I'll just go with those retention volumes for now.

Humm, yeah, that Derna link is circular.

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

I've not seen anywhere any video or eye witness about the movement of collapse of either dam so we don't know if it failed before overtopping or was just overtopped, and then promptly worn away very rapidly then water flow continued as per the storm surge water.

As said before, it looks to me like the past 20+ years resulted in virtually no water being stored for any appreciable period of time behind either dam so this could have lead to the the dam drying out in the heat and then becoming stressed when water arrive dint he space of a few hours or less up to its max capacity.

Or the initial period of rain filled them up and then they got hit by the peak hour or two of rain which did the damage.

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

It seems like if it was a spillway/drain problem, things would have happened just a bit slower than they did. I saw one story where someone was out making a video of the dam filling up, like at midnight. No video posted. He went home, then at around 01:30 he heard a very loud noise and was swimming a few minutes after that. I'd say it was a quick failure of the dam itself. Drainage system failure and internal washout of the drain works would probably take longer than an hour or so. Just guessing of course. That's as much as I've been able to deduce about the time line of things. Also fits with that supposed 20m initial wave someone (was it you?) mentioned. The loud noise and nearly immediate flood also fits. Would a tunneling erosion through the drain come with a loud bang? It also seems like the flow would have come a bit more gradually. Dam burst fits better I think.

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

My uncle Dennis was a geotekkie and was involved with the Portage Mountain Dam in BC. I wonder how any possible rainfall increases are addressed?

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

-Dik

My logic leads to increasing bypass capacity. Adding an additional one on the other side?
Or as a temporary or operating work around, you might be able to reduce the level permanately, although you'd lose power gen capacity if it was hydroelectric. There are times when high rainfall accumulates not due to extreme events over several months, then when a storm is forecast, they will prerelease water, before the storm arrives, to make room for the expected catchment. I think that must be the typical solution. Problem is, like this one, if high intensities become frequent and can overflow an almost or completely empty dam, it becomes a white elephant. You'd always be running on near empty and even empty is a risk. Only choice would be increase bypass, or demo.

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

Quote (human909)

In my home country Australia, we introduced an explicit factor in our wind code for cyclonic regions to account for the changing climate. Right now that factor is 1.0. But it was deliberately introduced acknowledging the currently quantifying increased risk.

Minor correction...the climate multiplier for wind speeds is already 1.05 in regions B2, C and D.

----------------------------------------------------------------------

Why yes, I do in fact have no idea what I'm talking about

As populations grow, the supporting structures must also. This often means upwards. As structures grow upwards they get less protection from the boundary layer effect so it makes sense that the wind loading factor should also be increased.

But (I presume) the factor is independent of height. It's a climate dependent factor, apparently set by region. Basic wind loads already have a height factor.

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

Dams which remain full of water and drain areas with a high silt load gradually fill up and hence the volume available to store water in the event of a large rainfall goes down relative to water height.

Most dams seem to be lifed for about 100 years at which point the volume of water they can store is about 10% if the volume it started with.

Even hydro dams basically just start to create a channel in the silt down to the hydro entrance but min water level will just keep going up.

These dams were essentially storm water holding "ponds". Only problem with that is no one seemed to think too much about what happened if the storm was bigger than the holding volume. So even if they both held ( say were made of concrete), the impact would still have been about as bad as the whole drained flow would simply overtop the dam and flow down like it would have in previous floods - the only saving grace being possible time to warn people and get an evacuation going - but difficult in the middle of the night in the middle of a hurricane in a country without a real functioning government.

Actual failure of the dams, especially the much larger one was a true disaster as it unleashed a HUGE wall of water onto the unsuspecting inhabitants, but very little would have stood up to that sort of rain fall. Only way around this sort of thing is to have good monitoring of the water levels and rain fall predictions, an effective alert system (sirens etc) and a population trained and able to move to higher ground. Some properties might be better to stay in place to avoid large numbers being caught in the open.

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

And that, my friends is the story. Thanks, LittleInch for the summary.

As far as the flooding goes, this sums it up pretty well.

"Climate change made the storm that devastated the Libyan city of Derna, killing thousands of people, up to 50 times more likely, experts say.

Up to 50% more rain had fallen as a result of human-caused greenhouse-gas emissions, climate scientists at the World Weather Attribution group found.

Years of conflict in the region compounded the vulnerability of people to flooding, the WWA report says.

And it turned the extreme weather into a full-scale humanitarian disaster.

The scientists used computer simulations to assess how much more likely such a storm was now compared with before the 1.1C of warming climate change has already brought.

But they cautioned a lack of data, particularly in Libya, meant considerable uncertainties in their findings."

https://www.bbc.com/news/science-environment-66854...

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

-Dik

Just think about the one just filled in Ethiopia

Is Egypt downstream...

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

-Dik

This disaster is an economic one, not engineering. There is a town called Valmeyer, Illiois that had enough money to move from the flood plain along the Mississippi to the bluffs above them. Problem solved, right? They were medium income and got FEMA money to do so. The same cannot happen in Libya.

I'm sure the other difficulty for evacuation would be that the streets would already be flooded and running fast from the storm. Possibly no power and no lights, few cars, so it would be people on foot running 5-10 miles in torrential rain, cold and threatening hypothermia, and the water already hiding obstacles and carrying debris. Few would have storm gear suitable for conditions. Where would they run to? Up steep slopes with water cascading down them?

I expect many of the dead were elderly or disabled.

There would need to be a huge facility for them to take shelter in. How would that be built and maintained?

The most telling part of the horror of the situation is lack of video recording the floodwaters sweeping through the city. Some before. Many after. None from the surrounding buildings that survived.

1503-44,

Roll time back to 2020.

Using any information available, what do you design the dam capacity to be?

Dont know just yet. I have the the wadi drainage area and the main channel mapped out in GEarth and just got the main channel,s elevation profile. I still have a few side channels to map and extract the slopes. I will build a Time of concentration model in Excel. Then I'll superimpose various rain intensities and their durations to calculate what the flow rates are at the dam locations and the safe flow rate that will not overflow the channel in the city. The difference of flow into the dam - safe flow out going into the channel through the city is the flow rate that should be stored in the dam.

The channel slope is 0.007, falling 482m in 70km. I don't think that is too bad a slope.
What makes this system bad, IMO, are

#1) lack of vegetation to soak up rain and mostly rock surface with high runoff coefficients and
#2) that the basin parallels the costal ridge and a lot of it is at 500m elevation.
#3 mostly very narrow channel that won't spill over and spread out into flat areas along the way down. What enters the channel isn't going anywhere except straight down the channel. The high head may keep water the flow moving fast even if the slope is not so great.

I live in a similar topography and when warm, wet air comes off the ocean and gets uplifted as it hits and climbs up the ridge, it usually starts raining first and quite heavily up on the ridge, right at that 500m elevation mark. That's about two km from me and here the sun is shining and you have no idea its raining cats & dogs up there until the cool air starts rolling down the slopes. 500m is just enough temperature drop to start squeezing rain out of saturated air. The entire basin probably took a good hit.

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

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

Quote (dik)

Up to 50% more rain had fallen as a result of human-caused greenhouse-gas emissions, climate scientists at the World Weather Attribution group

At least they aren't hiding it anymore.

As a follow-up, instead of trying to attribute this disaster to climate change so that funds can be misallocated, why not do something beneficial? Telling countries like Libya and Pakistan that we're going to reduce our GHG emissions isn't going to clear the silt from their flood control basins. Instead of trying to end the Western world as we know it, perhaps the UN should assemble some engineers to study flood control in historically flood prone areas with growing populations and poor political representation. That doesn't even mean building new dams, a simple survey could have warned Delma of the risks and encouraged residents to move to higher ground. We could build infrastructure, too. We'd probably get more bang for then buck in terms of lives saved building infrastructure in Africa and Pakistan than sending bombs to Ukraine.

Quote (Instead of trying to end the Western world as we know it)

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

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.

Is aerospace not the most fundamentally Western industry?

"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."

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."

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."

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

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.

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.

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."

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-quic...

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.

Quote (1503-44)

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".

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.

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/evid...

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

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.

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

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."

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.

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."

Quote (don't blame mankind for nature's propensity to throw a gutter ball once in a millennium or ten.)

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

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

-Dik

Been there done that. 1979.

That's a little snow, not a blizzard...

"The Atacama Desert, the driest and oldest desert on Earth, located in northern Chile, hides a hyper-arid core in which no rain has been recorded during the past 500 years. But this situation has changed in the last three years. For the first time, rainfall has been documented in the hyper-arid core of the Atacama, and contrary to what was expected, the water supply has caused a great devastation among local life. This is the main conclusion of an international study, published today in Scientific Reports titled "Unprecedented rains decimate surface microbial communities in the hyperarid core of the Atacama Desert," directed by researchers from the Center for Astrobiology (CAB). These recent rains are attributed to changing climate over the Pacific Ocean."

https://phys.org/news/2018-11-centuries-atacama-de...

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

-Dik

Another record breaking rain ...


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