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Major flooding in China; Update 9-22-2020

This topic can be found at:
https://sigforum.com/eve/forums/a/tpc/f/320601935/m/5840063274

July 24, 2020, 03:44 AM
Bytes
Major flooding in China; Update 9-22-2020
soflaac, thanks for that post. I had no idea of the destruction that would come from that dam breaking. That is unreal what could happen to those innocent people. All I can do is send hopes a prayers their way. This is awful. A total shit storm that we are watching Frown
July 24, 2020, 05:45 AM
Aglifter
I read a Chinese translated site, claiming it cannot catastrophically fail, because it’s a gravity dam.

Does that make sense?
July 24, 2020, 05:46 AM
Aglifter
I have seen small creeks wash 1000#+ boulders down stream
July 24, 2020, 07:06 AM
soflaac
I'm the last thing from a geologist or dam expert, but I believe some who are advised that even more than the dam structure itself failing the threat also includes the natural structure the dam is built on.

Once the base begins to be compromised, it can lead to cascading failure of the whole structure.



<><
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July 24, 2020, 07:45 AM
chellim1
quote:
I read a Chinese translated site, claiming it cannot catastrophically fail, because it’s a gravity dam.

Does that make sense?

By catastrophically fail, I think what they mean is come crashing down, all at once.
I hope they are right about that, but that dam is definitely compromised.

China admits Three Gorges Dam 'deformed' by flood
China says 2nd major flood caused 'displacement, seepage, deformation' of Three Gorges Dam
https://www.taiwannews.com.tw/en/news/3972343



"Some things are apparent. Where government moves in, community retreats, civil society disintegrates and our ability to control our own destiny atrophies. The result is: families under siege; war in the streets; unapologetic expropriation of property; the precipitous decline of the rule of law; the rapid rise of corruption; the loss of civility and the triumph of deceit. The result is a debased, debauched culture which finds moral depravity entertaining and virtue contemptible."
-- Justice Janice Rogers Brown

"The United States government is the largest criminal enterprise on earth."
-rduckwor
July 24, 2020, 09:18 AM
ChuckFinley
Yes, the twitter video shows the whole dam just falling down at once and the water proceeding. I didn't find that all that illustrative.




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July 24, 2020, 11:15 AM
soflaac
quote:
Originally posted by ChuckFinley:
Yes, the twitter video shows the whole dam just falling down at once and the water proceeding. I didn't find that all that illustrative.


I'm kinda doubting the dam breaking apart at once wasn't really the point of the video. Wink



<><
America, Land of the Free - because of the Brave
July 24, 2020, 11:45 AM
StarTraveler
That article mentions that the dam has deformed but that it is elastic deformation. By definition, elastic deformation means that the material hasn’t yielded and the deformation isn’t permanent. When the load is removed, the material should resume its original shape (or at least part way, since all of the load will never be removed).

I hope the Chinese government officials who reported this are telling the truth, but, with like anything they say, I have my doubts.


***

"Aut viam inveniam aut faciam (I will either find a way or make one)." -- Hannibal Barca
July 24, 2020, 12:22 PM
Il Cattivo
Does anyone know how much elasticity there would be in the materials used to construct the dam? I'm trying to avoid having a Rosie O'Donnell moment.
July 24, 2020, 12:47 PM
BBMW
There's another dam on the Yangtze not far downstream of the Three Gorges Dam. I have to wonder how that's holding up also.
July 24, 2020, 01:00 PM
signewt
I was around 'dam builders' much of my pre-adult life. My dad & his clan were all in various heavy construction trades. They readily offered their opinions of whatever the latest snafu arouse from various projects and the occassional failure of such.

Earth fill vs concrete vs combination designs are all complicated by a wide range of variables. Some are capable of some degree of 'elastic deformation' without immediate structure failure and some aren't.

I haven't seen convincing arguments regarding elasticity & temporary deformation in huge concrete dam components.


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July 24, 2020, 02:45 PM
Kuisis
Does anyone with engineering experience have a prediction about what will happen at the dam? You would think there would be some serious evacuations if failure was certain, but who knows in China? Hopefully the rain will stop.
July 25, 2020, 12:20 AM
ensigmatic
quote:
Originally posted by Kuisis:
Does anyone with engineering experience have a prediction about what will happen at the dam?

Read back a few pages. We had a dam inspection expert give his analysis and opinion.

TL;DR: He thought it was probably going to hold. But that was before Yet More Water, the reports of some "non-structural" failures, the admissions of some deformation, and before leaks had been reported, IIRC.



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"If we let things terrify us, life will not be worth living." -- Seneca the Younger, Roman Stoic philosopher
July 25, 2020, 05:50 AM
Woodman
quote:
Originally posted by Kuisis:
Does anyone with engineering experience have a prediction about what will happen at the dam?
Short of skimming all ten pages, some facts which broadened my knowledge come to light on this post and page:

https://sigforum.com/eve/forums...000026274#4000026274
July 25, 2020, 07:31 AM
Blume9mm
Okay, maybe this was answered already... why don't then just let more water out? Seems to me when you build a damn you would give it a way to let most of the water escape with out it backing up to over flow on the high side... yes, I know it will flood down stream but a flood is better than a big wave.


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"Runs with Scissors"
July 25, 2020, 07:48 AM
Sig209
quote:
Originally posted by Blume9mm:
Okay, maybe this was answered already... why don't then just let more water out? Seems to me when you build a damn you would give it a way to let most of the water escape with out it backing up to over flow on the high side... yes, I know it will flood down stream but a flood is better than a big wave.


short answer is they have been letting out an extremely high 'outflow' of water

flooding downstream has been bad

maybe even close to the 'max' outflow of what they can -- iirc all the floodgates have been opened

the volume of water from the flooding has been extreme

=================================


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July 25, 2020, 09:45 AM
jaaron11
The reason they are not letting more water out is either because they can't or they don't want to. I know that sounds trite, but that's the deal. We are focusing on the Three Gorges Dam because of its size, but there are many dams in the Yangtze system. It's a balancing act. If you let more water out at Three Gorges, you increase flooding and pressure on the downstream dams, some of which are likely in worse shape structurally than Three Gorges. So they are probably letting out as much as they need to at Three Gorges to keep their safety readings in the green (or maybe yellow in this case), while trying to minimize downstream impacts.

It could also be that they are already at maximum discharge. All of the primary spillway gates are open, based on what I've seen reported. Modern dams, even in China, should have an emergency spillway to pass water in the event that the primary spillway is inoperable or is overwhelmed. It's generally only used as a last resort to prevent a catastrophic failure. See the Oroville Dam crisis from a couple of years ago for how an emergency spillway can save the day. Three Gorges does not have a designated emergency spillway that I can see. My presumption is that the locks and/or ship lift are designated as the emergency spillway. I'd be curious to know if they are using those to pass water right now at the risk of damaging the structures. That would tell us something about their level of concern.

I also note that most of the discussion and concern has been around the primary dam, the massive concrete structure that shows up in all of the pictures. This flooding is also putting pressure on the south saddle dike adjacent to the main dam. You can see it on aerial photographs running perpendicular southwest of the main dam. That is an earthen structure that is likely more susceptible to failure.

Regarding deformation, anytime stress is added to a system beyond what it previously seen, deformation is going to occur. It's the natural stress-strain relationship of materials. If this is indeed elastic deformation, as China has claimed, it's not a big deal. Even it's plastic deformation, meaning permanent, it may not be a big deal. I don't trust any information coming from an official Chinese source, so who knows what the actual numbers are.

Nothing that I've seen makes me think failure is imminent or even likely. However, I'm hesitant to speculate on what will happen without good data, and nothing coming out of China appears to be good data at the moment.


J


Rak Chazak Amats
July 25, 2020, 10:05 AM
DennisM
Given the PRC's talent for understatement, if they're admitting to ANY concerns about the dam...
July 25, 2020, 10:11 AM
chellim1
quote:
Nothing that I've seen makes me think failure is imminent or even likely. However, I'm hesitant to speculate on what will happen without good data, and nothing coming out of China appears to be good data at the moment.

Thanks for your informed analysis, jaaron11.
Although I loathe the CCP, I pray for the people.



"Some things are apparent. Where government moves in, community retreats, civil society disintegrates and our ability to control our own destiny atrophies. The result is: families under siege; war in the streets; unapologetic expropriation of property; the precipitous decline of the rule of law; the rapid rise of corruption; the loss of civility and the triumph of deceit. The result is a debased, debauched culture which finds moral depravity entertaining and virtue contemptible."
-- Justice Janice Rogers Brown

"The United States government is the largest criminal enterprise on earth."
-rduckwor
July 25, 2020, 10:29 AM
jaaron11
quote:
Originally posted by DennisM:
Given the PRC's talent for understatement, if they're admitting to ANY concerns about the dam...

Agreed. That’s what gives me the most concern.


J


Rak Chazak Amats