How much flow can the spillways handle? There still has to be a maximum designed flow for all systems. Would be curious what that number is.Gold Star ntxVol said:It won't go over the top of the damn. They should have a spillway off to the side so, if the level gets high enough, it will spill over, uncontrolled. It will spill over (uncontrolled) until the level drops back down below the spillway level. It should never go over the top of the damn.American Hardwood said:
The question for me is whether the dam can hold up if it ends up going over the top. I'm not enough of an engineer to run calculations but it would seem that the lateral force at the very top is going to increase dramatically even with a few meters of water running over the top.
China Rivers Flooding ...... 3 Gorges Dam could fail ?
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Last: 4 yr ago by richardag
Looks like they have a center spillway.
A little more info.
I'm guessing the center spillway kicks in at 175 meters. This suggests outflow at that point can go all the way to 102,500 m^3/sec. I suppose stuff starts to go pear shaped when the water level reaches 180.4m. And the structure is over topped at 185m.
From
http://www.chincold.org.cn/dams/rootfiles/2010/07/20/1279253974143251-1279253974145520.pdf
A little more info.
I'm guessing the center spillway kicks in at 175 meters. This suggests outflow at that point can go all the way to 102,500 m^3/sec. I suppose stuff starts to go pear shaped when the water level reaches 180.4m. And the structure is over topped at 185m.
From
http://www.chincold.org.cn/dams/rootfiles/2010/07/20/1279253974143251-1279253974145520.pdf
Okay. Thanks!Quote:
That would be bad just because of the massive inflow it would create.
I hope that wall would spread out inside the reservoir behind the damn such that by the time it reached the damn it wouldn't be a "wall" anymore but more like a large wave only a few feet high. Still could be bad even then depending on how much pressure is already on the damn.
So it sounds like the projected maximums are well within the design parameters unless one of the upstream dams fail.
Design parameters are one issue. Actual construction parameters are another.American Hardwood said:
So it sounds like the projected maximums are well within the design parameters unless one of the upstream dams fail.
I don't know but it's a lot.American Hardwood said:How much flow can the spillways handle? There still has to be a maximum designed flow for all systems. Would be curious what that number is.Gold Star ntxVol said:It won't go over the top of the damn. They should have a spillway off to the side so, if the level gets high enough, it will spill over, uncontrolled. It will spill over (uncontrolled) until the level drops back down below the spillway level. It should never go over the top of the damn.American Hardwood said:
The question for me is whether the dam can hold up if it ends up going over the top. I'm not enough of an engineer to run calculations but it would seem that the lateral force at the very top is going to increase dramatically even with a few meters of water running over the top.
Lake Texoma was designed by the Corps of Engineers such that it should only go over the spillway once every 100 years. It's gone over 4 times since it was built. In 2015 it set a record at almost 6 feet above the spillway.
That's not the Red River in the background.
This is true of course. For something of this magnitude you would think that construction standards would be very strict, but it is the Chinese so who knows. Kinds surprised it hasn't failed already honestly.aggiehawg said:Design parameters are one issue. Actual construction parameters are another.American Hardwood said:
So it sounds like the projected maximums are well within the design parameters unless one of the upstream dams fail.
gravity dams are the kinds of things commies can do ok generally. A big blob of concrete heavy enough to withstand the designed flow by its weight alone.
now, whether they accounted for the substrata appropriately or left so many dead (or alive) bodies and other meat popsicles and air bubbles in it that it fails anyway, who knows.
now, whether they accounted for the substrata appropriately or left so many dead (or alive) bodies and other meat popsicles and air bubbles in it that it fails anyway, who knows.
I am a meat popsicle
Yeah, maybe the engineers allowed for a certain amount of biological aggregate in their concrete design mix.cbr said:
gravity dams are the kinds of things commies can do ok generally. A big blob of concrete heavy enough to withstand the designed flow by its weight alone.
now, whether they accounted for the substrata appropriately or left so many dead (or alive) bodies and other meat popsicles and air bubbles in it that it fails anyway, who knows.
American Hardwood said:This is true of course. For something of this magnitude you would think that construction standards would be very strict, but it is the Chinese so who knows. Kinds surprised it hasn't failed already honestly.aggiehawg said:Design parameters are one issue. Actual construction parameters are another.American Hardwood said:
So it sounds like the projected maximums are well within the design parameters unless one of the upstream dams fail.
I thought there was suggestion earlier in this thread that China did in fact skimp on construction standards, in spite of being advised not to.
A dam failure would not be good for our struggling economy.
well, user name checks out!KorbinDallas said:
I am a meat popsicle
What doesn't make sense is water then doesn't come flooding in despite broken glass. There is something strange going on.American Hardwood said:What exactly is this video depicting? Is the inflow of water into the subway pressurizing the air to cause these storefront systems to blow out? Kind of what it looks like.thomas20:29 said:
Wuhan subway...
Essentially slave labor is usually...uhm...uninspired to do a great job when direct supervisors aren't in sight.cisgenderedAggie said:American Hardwood said:This is true of course. For something of this magnitude you would think that construction standards would be very strict, but it is the Chinese so who knows. Kinds surprised it hasn't failed already honestly.aggiehawg said:Design parameters are one issue. Actual construction parameters are another.American Hardwood said:
So it sounds like the projected maximums are well within the design parameters unless one of the upstream dams fail.
I thought there was suggestion earlier in this thread that China did in fact skimp on construction standards, in spite of being advised not to.
Not quite. Designing for a 100 year event means designing for an event that has a probability of occurrence equal to 1 percent in any given year. Also, there are multiple 100 yr events when considering duration. 24-hr, 100yr event is a typical design standard for normal service hydraulic structures. For emergency spillways and outlets, you have to pass the probable maximum flood without compromising the dam.
T&P for Kingwoodtk for tu juan said:PearlJammin said:Every day or every second?agent-maroon said:CanyonAg77 said:Googled up the numbers, apparently the normal flow from the Mississippi is <17,000 CMS, so we're talking 4.5x the Mighty Miss.akm91 said:Yikes!Quote:
On the Yangtze River, the inflow of water into the reservoir behind the massive Three Gorges Dam hit a record 72,000 cubic meters (2.5 million cubic feet) per second, state media said. The inflow is expected to peak Thursday at 76,000 cubic meters per second, the Ministry of Water Resources said.
Although, it can't touch the Amazon, at 209,000 CMS.Quote:
Before the completion of the Three Gorges Dam, water volume in the Yangtze was about 529,000 cubic feet (15,000 cubic meters) at the end of the Three Gorges region and up to 1,100,000 cubic feet (31,100 cubic meters) at its mouth, according to Encyclopaedia Britannica. These numbers have decreased somewhat due to the dam. The suspended sediment load (sediment that is carried in the water flow and never quite settles on the bottom) at the mouth of the river is about 478 million tons a year one of the highest sediment loads of any river on earth.
Calculated 76000 cubic meters/sec to be 1.5 cubic miles of water flowing every day.
Day
You could drain and fill up Lake Conroe 12 times each day
Gold Star ntxVol said:I don't know but it's a lot.American Hardwood said:How much flow can the spillways handle? There still has to be a maximum designed flow for all systems. Would be curious what that number is.Gold Star ntxVol said:It won't go over the top of the damn. They should have a spillway off to the side so, if the level gets high enough, it will spill over, uncontrolled. It will spill over (uncontrolled) until the level drops back down below the spillway level. It should never go over the top of the damn.American Hardwood said:
The question for me is whether the dam can hold up if it ends up going over the top. I'm not enough of an engineer to run calculations but it would seem that the lateral force at the very top is going to increase dramatically even with a few meters of water running over the top.
Lake Texoma was designed by the Corps of Engineers such that it should only go over the spillway once every 100 years. It's gone over 4 times since it was built. In 2015 it set a record at almost 6 feet above the spillway.
That's not the Red River in the background.
As stated, once in 100 years isn't really once every 100 years. It's a (very) long term average or probability. You could have 4 events in 20 years, then none for 400, or none for 200, 4 in a short span, and then none for another 200. They're theoretically random, so clustering and long periods of quiet are to be expected. You won't have one, "every 100 years," because that's not random.
Then there's the, "once in a hundred years," part. How do we know the probability of a large scale event or its long term average when we have little or no history of it happening? Like earthquakes. How do we know the probability of large earthquakes in earthquake prone regions without ever having recorded them there and without having a long term, detailed record of geologic activity? The answer is the distribution of smaller events in a time frame and their occurrence rates over time. The rate of occurrence for events in relation to size can tell us how common larger, unseen events are and even give an idea of the maximum event size. From there, we can build probabilities of larger events because they follow a distribution. The problem is, it's an estimated distribution still based on limited observations. Estimate wrong, and a once in 100 year event could really be something that happens once about every 50 years or 25 years.
The probability also changes with a changing landscape. With increases in development, you can change runoff patterns and groundwater patterns. That can cause areas to flood with less rain because the water isn't absorbed into the ground like it used to be. That makes rare flood events more common because flooding doesn't require rare weather conditions to happen anymore.
ETA Since maximum probable event is mentioned, if you incorrectly estimate the occurrence rate to magnitude distribution of an event, not only can large events happen more often than you estimate, the magnitude of the largest probable event increases as well. As magnitude increases, probability decreases and approaches 0. With undercounted smaller events, the right tail of the distribution is slightly depressed, and the true probability of an event becomes negligible at a higher magnitude than what you expect.
These distributions are also based on relatively short term observations of random, non-uniformly distributed events. If you are observing during a lull, which is more likely than observing during a cluster of activity because they are longer, then you are undercounting. The drawback to these types of estimates is that the observation period may not be long enough to be random sampling even over very long time periods because human lifespans are nothing compared to weather and geologic variability. What seems like a long observation period really isn't. You need to understand the variability of the distribution to determine the likelihood of being in a lull, a period of high activity, or something closer to average in the observation period compared to the entire distribution. Basically, are you at the mean or regressing to it.
That's a great summary
Yes it is!CivilAg10 said:
That's a great summary
ABATTBQ11's posts there is the kind copy and past the meat of it, save it to a clipboard crediting author, and keep as kind of a version of a good Wikipedia file.
This by the way, is one of the reasons this board remains good --whether a liberal or conservative poster, some real information gems in distilled form often appear.
plain_o_llama said:
Looks like they have a center spillway.
A little more info.
I'm guessing the center spillway kicks in at 175 meters. This suggests outflow at that point can go all the way to 102,500 m^3/sec. I suppose stuff starts to go pear shaped when the water level reaches 180.4m. And the structure is over topped at 185m.
From
http://www.chincold.org.cn/dams/rootfiles/2010/07/20/1279253974143251-1279253974145520.pdf
The center spillway is gated. It's not an uncontrolled release over the top.
CivilAg10 said:
Not quite. Designing for a 100 year event means designing for an event that has a probability of occurrence equal to 1 percent in any given year. Also, there are multiple 100 yr events when considering duration. 24-hr, 100yr event is a typical design standard for normal service hydraulic structures. For emergency spillways and outlets, you have to pass the probable maximum flood without compromising the dam.
Username checks out.
CivilAg10 said:
Not quite. Designing for a 100 year event means designing for an event that has a probability of occurrence equal to 1 percent in any given year. Also, there are multiple 100 yr events when considering duration. 24-hr, 100yr event is a typical design standard for normal service hydraulic structures. For emergency spillways and outlets, you have to pass the probable maximum flood without compromising the dam.
Spot on! Additionally, reservoirs designed for flood control can briefly hold water pending down steam conditions; ie. if it's safe to do so. So multiple lines than 1% chance storms could pile up, leading to a release.
I read up on the conditions fir gate operations at Mansfield (lake travis) during the recent floods on the Llano. Their releases were tied to water levels in lake Austin, Bastrop, and LaGrange.
Btw, the operations manual for lake Conroe has a point where the gates will be opened till they're completely above the water line. That's goodbye I45, goodbye Kingwood inflows though.
The Probable Maximum Flood would make Noah look unprepared.
Why can't I see this tweet with my phone?
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LOL
Ags4DaWin said:
LOL
It can make sense if the water is flowing in to a lower level. I'm thinking the water is rapidly flooding a tunnel or chamber compressing trapped air. Perhaps a gate or door of some type gives way due to the increased pressure and results in explosive decompression. The shockwave travels down the tunnel to this area and blows out the windows sequentially as the shockwave passes. The water that originally compressed the air finds another pathway to flow or follows the compressed air shockwave more slowly and doesn't appear in the video. That's my theory.titan said:What doesn't make sense is water then doesn't come flooding in despite broken glass. There is something strange going on.American Hardwood said:What exactly is this video depicting? Is the inflow of water into the subway pressurizing the air to cause these storefront systems to blow out? Kind of what it looks like.thomas20:29 said:
Wuhan subway...
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