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Old 14th Feb 2017, 16:41   #21 (permalink)
 
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You could well find that all the people responsible for mistakes in design and construction are no longer alive......Those responsible for maintenance are around though. Finding which politicians and bean counters stopped the cash for proper maintenance will prove impossible......
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Old 14th Feb 2017, 16:52   #22 (permalink)
 
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If this structure fails, and people die, I venture to say all politicians and State engineers might have to run for cover.....every one of them. The mob is not particular, and does not demand due process.
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Old 15th Feb 2017, 02:58   #23 (permalink)
 
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Earthquake

It gives one pause to contemplate the potential results of a 5+ Richter Scale jitter along the San Andreas Fault, which lies not so far away from this behemoth structure.

When I was a younger (and wiser) man, I dwelled in an home in Daly City, California, which sat astride the aforementioned. For real! I lived in fear, believing that I would be swallowed by Mother Earth at any instant; as I listened to others nearby, who reassured me that the greatest damage that would accrue to a major quake would be the 10 feet (3 meters) of shattered plate glass which would plummet earthward from the towering skyscrapers in downtown San Francisco. "Just don't be downtown when it happens!", they would say. I took little comfort in their platitudes, save for the fact that nothing other than minor tremors took place when I was there, for a long year full of trepidation...

Then I moved to Cincinnati. The day after I arrived, the New Madrid fault gave us a 4.0 premonitory tremor. A couple of jolts, strong enough to shake treasured porcelains from lovingly built shelving, followed by the same sort of tremors that new lovers present one another after a long kiss.

The last time that fault let loose, it rang church bells in Boston! The Mississippi ran backward. Fontanelles erupted in corn fields throughout the Midwestern United States. I thought about moving back to Cali, but even I am not quite that wild and crazy!

Still Awaiting The BIG ONE!

O'B
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Old 15th Feb 2017, 15:06   #24 (permalink)
 
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Virtually all glass in downtown skyscrapers is tempered. It shatters into small pebbles when it fails. You won't be sliced apart, but you may have wounds that resemble being shot with a shotgun....depending on the height of the glass.

The Oroville dam is constructed of dirt, hence "an Earthen Dam".

When you work up the courage, look for the following word related to earthquakes and structural failure:

Liquefaction.....
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Old 15th Feb 2017, 16:25   #25 (permalink)
 
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The Oroville dam is constructed of dirt, hence "an Earthen Dam".
Only part is.
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Old 15th Feb 2017, 17:05   #26 (permalink)
 
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Earthen

Quote:
The Oroville dam is constructed of dirt, hence "an Earthen Dam".

"Only part is."


Yes, the "dam" part.... The spillways and generation plant are concrete, but the dam structure is.....dirt.

(The bottom hundred feet or so, containing the power plant, concrete.)

Last edited by Concours77; 15th Feb 2017 at 17:16.
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Old 15th Feb 2017, 18:32   #27 (permalink)
 
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You kinda have to understand that water politics are huge in California. Have been for a century or more. As the old saying goes:

"In southern California, if any of the water in a river actually reaches the ocean, that is considered a 'criminal waste.'

In northern California, if any of the water in a river doesn't reach the ocean, that is considered a 'criminal waste.' "



I expect there may have been some "droughtophobia" as a hole in the cheese for this semi-disaster.

After 4 years of being hammered by extreme drought, I expect the attitude statewide-wide, once the rains came, was "Let's grab all we can get, while the getting is good!"

It would have been politically difficult, once the reservoir filled to a reasonable level (say 75%), to open the flood gates and hold it with a "reserve" capacity in case more rain came. Which I am sure the water "pros" would have preferred.

There would have been nightly newscasts with video of "precious" water pouring out the gates, and politicians and the farm lobby and probably most of the population would have gone ballistic.

So they kept topping it up, and topping it up - and then the rains didn't quit.....
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Old 15th Feb 2017, 19:54   #28 (permalink)
 
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It isn't politics, it's money, I know redundant....
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Old 15th Feb 2017, 20:13   #29 (permalink)
 
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They were releasing an estimated 750,000 gallons per second the other day (probably US gallons, before anyone asks). That is an incredible amount of water that dropped the lake level a few feet in 24 hours. Let's hope for once that the weather bods have got it totally wrong about the forecasted approaching rains and disaster will be averted.
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Old 15th Feb 2017, 22:23   #30 (permalink)
 
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I don't want to see anyone hurt, but in California's case, I'll make an exception. Thus is entirely an unforced error brought in by idiot politics, poor budgeting and political correctness.

GF
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Old 15th Feb 2017, 22:38   #31 (permalink)
 
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Trump caved....and authorized Federal Emergency funds for the Oroville Dam situation......I hope he got Guv MoonBeams Knackers in a jar on an Oval Office Shelf as payment.
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Old 15th Feb 2017, 22:47   #32 (permalink)
 
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Yes, the "dam" part.... The spillways and generation plant are concrete, but the dam structure is.....dirt.
To be clear, I'm no expert on dams, but the news doesn't seem to completely agree with you. Now if you're an expert in the field, than I defer to you. If not, there might be conflicting information out there.


http://www.vox.com/science-and-healt...ood-evacuation
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Old 15th Feb 2017, 22:52   #33 (permalink)
 
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In an area prone to seismic activity, it seems reasonable to expect that the risk of a local earthquake happening is increased due to the additional weight of water behind the dam. Additionally, rainfall will be seeping down through the rocks and lubricating fault lines that have been drying out for years, while stresses have been building. A broken spillway might be the least of their problems in a couple of months. It seems incredible that a dam holding back what is essentially a 1,000 foot deep lake is just constructed from packed earth with a concrete facing in a known earthquake zone.
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Old 16th Feb 2017, 00:19   #34 (permalink)
 
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As the Byzantines demonstrated millennia ago, a wall filled with rubble and earth will withstand quaking a lot better than a fully stone-built one.
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Old 16th Feb 2017, 00:45   #35 (permalink)
 
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Hi West Coast,

I was merely pointing out that the actual dam is built of soil...and the dam itself is doing fine. The structures in distress are the main spillway, and the solid "emergency" dam. It is actually a dam only. There is no controlling what amounts to a 600 meters long "berm". It was overtopped Saturday morning, and immediately the outfall gave up its overburden of native soil. The dam crew started placing rocks and sand after the level of the lake itself dropped back below the so-called "emergency" spillway....

I have been following the crisis on media. A local heli pilot has been bird dogging the situation in fine fashion....

Saturday evening, the media reported a requirement for immediate evacuation, and announced "the spillway will fail in the next few minutes." It didn't, but the locals, 188,000 of them, spent the next three days spread out above and beyond the predicted floods borders.

My dam experience is limited to building a few small ones, and extensive grading and heavy equipment operation. It didn't take an expert to notice the poorly laid out and insufficiently designed problem areas.

The hysteria evident in the pronouncement by the dam managers likewise emphasized they themselves had no confidence in the structures.

One thing I have noticed is the State's unusual designs, in that the concrete pour lacks reinforcing steel, evident in the way the "pads" failed like soda crackers, seemingly independent of the surrounding pads. That might be excused, in that the main spillway needs to not be monolithic, a failure of a large area could pull upstream concrete down the chute, and potentially fail the spillway hub, which could have wiped out far more people than if the thirty foot "berm" gave way.
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Old 16th Feb 2017, 02:18   #36 (permalink)
 
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Our biggest local water supply and flood mitigation dam here is SE Queensland - Wivenhoe Dam - is interesting in the it can best be described as two dams sitting one on top of the other. When the water storage dam is reported as being 100% full it holds 1,165,000-megalitres (256109 imp gal; 308109 US gal). However there is still another 1.45 million megalitres (320,000106 imp gal; 380,000106 US gal) of capacity for flood mitigation.

In other words, the flood mitigation dam is 1.25 times greater than the water storage dam; but they are both contained within the same physical structure. So the dam can actually hold 225% of it's 'declared' capacity - something that many people cannot get their heads around.

There are legally enforceable regulations that must be followed when the storage dam reaches 100% capacity and the flood mitigation dam starts filling. Sounds like some planning along these lines might be helpful at Oroville.

Some other interesting comparisons:

Oroville Volume 4.36 km3 (1.7 x larger than Wivenhoe total capacity)
Wivenhoe Volume: Total: 2.61 km3 (Storage:1.16 km3 Flood: 1.45 km3)

Oroville spillway capacity is 150,000 cu ft/s
Wivenhoe spillway capacity is 420,000 cu ft/s (2.5 times bigger than Oroville)

The planners and builders for Wivenhoe did have more knowledge to draw from (built 1983, Oroville built 1957) but it seems that they gave better thought to flood mitigation and water release capacity. Of course these factors are influenced by local issues (topography, weather/precipitation records etc) but there does appear to be some scope for reconsideration of some of Oroville's operating procedures.
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Old 16th Feb 2017, 02:35   #37 (permalink)
 
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Quote:
it seems that the main overflow is not one continuous concrete structure, but rather made from, albeit large, concrete plates. A bit like a highway or an apron.

To my laymans eyes, this seems unwise, as the gaps between those individual plates can never be tight.
Concrete has to be poured in sections, for several reasons.
One, the concrete pour needs construction joints, due to how it is poured and the cure rate. Without joints, it would continue to flow down the hillside, and/or the concrete would not be able to be finished properly.
Second, with the thermal coef of expansion, there needs to be joints, or it will expand and crack apart. A floor or building in CA is required to have some sort of expansion joint every 100 sq feet to prevent cracking.

What you are seeing is a failure of the subgrade, rather than a failure of the concrete. It does not look like there was any way to prevent the rainwater from washing away the hillside under the concrete spillway.

In comparing different dams, there is quite a bit more to look at, especially what happens downstream, the channel, and where it goes. Note that at Oroville, there is flow control at the base of the dam which power is generated, a secondary spillway, and the emergency spillway. The flow control and spillway have a capacity of around 300,000 fps.

Wivenhoe has a combined spillway. From the Wivenhoe flood images, having the capacity to dump more water is not always a good thing downstream.




Last edited by underfire; 16th Feb 2017 at 03:02.
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Old 16th Feb 2017, 06:44   #38 (permalink)
 
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David, interesting that you mention Wivenhoe. The arrangement of flood mitigation storage above full supply level in not uncommon, but it's unusual (in NSW where most of my work was) for flood mit. to be so big. Am I correct in thinking the flood mit. was increased after the 2011 floods?
I've done a few flood op. procedures for dams, but none so complicated as Wivenhoe - large dam, large flood-prone area downstream, tide-affected levels downstream, and a huge amount of political pressure.
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Old 17th Feb 2017, 01:02   #39 (permalink)
 
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Concrete has to be poured in sections, for several reasons.
I saw a documentary about the building of the Hoover Dam some time ago, and they said they had to build it in chunks and let the concrete set, because, if they'd poured it all in one go, it would take a thousand years or more to completely set.
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Old 17th Feb 2017, 01:13   #40 (permalink)
 
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Not an insignificant hole.


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