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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Some geologic info in this video starting at ~ 1:30. They are mapping the structural characteristics of the bedrock, mainly the location and orientation of joints (fractures) and shear zones in the recently eroded emergency spillway area.
[Click to View YouTube Video]
Note the geologist refers to the meta-volcanic bedrock as amphibolite, which is a higher grade of metamorphism than greenschist facies.
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August West
Trad climber
Where the wind blows strange
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I dunno, I would think that's somewhat wildly optimistic. There's really no 'repairing' the spillway. They can attempt to stabilize the what remains of the upper spillway, but that's about it. If they still have to use it, and they likely will, it will still be cutting away in its new channel and filling up the river below with debris and that will have to cleared after each time they use it. The only solution is an entirely new spillway. As I said, I just don't know how or when they'd be able to pull that off without draining the lake substantially as you suggest as it would be a multi-year project.
I guess I have more faith in our public institutions than you do. This is no longer a hypothetical situation. The lower spillway is damaged and the upper spillway is suspect. Not fixing it could cause hundreds or thousands of deaths with a catastrophic failure.
I'm guessing the cost of fixing it is over $500 million. (My current wild guess is 1 billion).
Yes, you can drain the lake for years if that is what it takes. The governor declares it an emergency situation and that is that.
Are farmers really going to scream that the lives of thousands of people should be risked so they can grow a few almonds?
It isn't that big of deal. Drain the lake. Pay the farmers a few tens of millions (per year) until the dam is fixed to cover the value of the lost crops.
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Reilly
Mountain climber
The Other Monrovia- CA
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Why does the lake have to be drained much below the spillway level?
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Jon Beck
Trad climber
Oceanside
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Pray for a drought?
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Why does the lake have to be drained much below the spillway level?
I suspect to create enough storage capacity that another unforeseen series of "pineapple express" storms doesn't overtop the spillway, especially if the repairs take longer than 9 months.
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WBraun
climber
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A quarry blast, not an earthquake.
The quarry blast shook the earth .....
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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The quarry blast shook the earth ..... yes of course, but did not cause the original break in the spillway
WBraun: more likely that you would fall leading the 1st pitch of Outer Limits, than the minor ground shaking from that quarry blast broke the spillway :-)
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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The Main Spillway shotcrete band aid has been completed. Ready for action starting next week...
It will be interesting to see if the shotcrete prevents any additional headward erosion under the spillway once the action starts.
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Winemaker
Sport climber
Yakima, WA
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Seems like it wouldn't be too difficult to attach some nicely rolled steel plate off the end of the broken spillway; give the welders some overtime too......... But seriously, steel could prevent undercutting, more durable than shotcrete and mesh; it wouldn't be taking the whole water load, just the backwash.
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Mar 10, 2017 - 09:43am PT
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this might be what DMT is referring to^^^...
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healyje
Trad climber
Portland, Oregon
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Mar 10, 2017 - 10:01am PT
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I guess I have more faith in our public institutions than you do. This is no longer a hypothetical situation. The lower spillway is damaged and the upper spillway is suspect. Not fixing it could cause hundreds or thousands of deaths with a catastrophic failure.
I guess I don't think of it as a matter of faith in public institutions so much as just considering the tough realities they're facing. It's not a matter of fixing it or not fixing it so much as how the hell do you 'fix it', when, and how do you pull that off.
Replacing the whole thing and doing it right this time is really the only intelligent option, but doing it would likely take 2-3 years. That means they would need to take the reservoir down to a level that flow through the powerhouse alone would handle the lake level for the duration of the project.
As it is now, any use of the spillway is going to bring more debris in the diversion pool shutting down the powerhouse and causing a cycle of spillway flows and digging out the pool. I would think they would try to avoid that scenario at all cost.
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neebee
Social climber
calif/texas
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Mar 10, 2017 - 12:55pm PT
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hey there say, DMT... THANKS for sharing... :)
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Mar 10, 2017 - 01:56pm PT
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DMT: that Mavin's Notebook website is a great resource...
I always thought it was amazing that the drainages west of the Minarets crest flow into the Sacramento Delta
Here's the Feather River watershed. What is the highest Peak in the Feather River watershed?
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Bob Harrington
climber
Bishop, California
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Mar 10, 2017 - 04:50pm PT
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The headwaters of the Middle Fork of the San Joaquin are actually east of the Minarets (maybe that's what you meant?).
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Mar 10, 2017 - 07:41pm PT
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Bob Harrington: yes, that's what I meant. Thanks for pointing that out.
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tuolumne_tradster
Trad climber
Leading Edge of North American Plate
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Mar 12, 2017 - 05:36pm PT
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I suspect they're drilling into any significant voids found beneath the main concrete spillway using the GPR to squeeze cement and seal them.
Check out this excerpt from the 1962 report "INSPECTION OF OROVILLE DAM SPILLWAY SITE AND
DISCUSSION OF OROVILLE DAM MODEL STUDIES, STATE OF CALIFORNIA DEPARTMENT OF WATER RESOURCES
We then proceeded up the mountain side to the site of the spillway,mwhich will be off channel near the right dam abutment. The party then walked to the river channel down the draw in which the spillway channel will be constructed. We stopped at each drill hole aud
examined a log of the hole. Cores from the drill holes were not available at the dam site and were not examined.
The spillway is located in a natural saddle with upstream topography that should give good flow conditioms in the spillway approach. The rock in the spillway channel is amphibolite that is hard and tough where fresh and soft where weathered. Overburden in the area varies from a few feet to over 50 feet. The drill hole logs showed that the rook is fractured, and excavations up to 70 feet are required in places to reach sound rock.
From a 2008 report on Dam Safety posted on the MetaBunk thread...
http://www.hydroworld.com/articles/hr/print/volume-27/issue-2/technical-articles/dam-safety-evaluating-spillway-condition.html
Hydrologic conditions that can lead to failure modes in dam spillways...
– Existing structural damage that compromises the spillway;
– Flows that exceed spillway capacity;
– Cavitation damage;
– Significant stagnation pressures that can lead to hydraulic jacking or structural collapse; and
– Foundation erosion related to seepage or groundwater.
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neebee
Social climber
calif/texas
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Mar 12, 2017 - 05:38pm PT
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hey there say... once again, guys... thanks so much for sharing...
i again, enjoyed that 'river run' map...
:)
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TLP
climber
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Mar 12, 2017 - 06:37pm PT
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More great posts, tradster. Keep 'em coming. I'll put my wager chip on e) foundation erosion. Maybe d) but that seems much less likely. Seemed like there were a lot of leaks, that would have moderated the pressure. For all the talk about cavitation, my understanding of the good examples of failure or near failure from that cause, it results in a different pattern of initial damage than the photos we've seen from the beginning. So, I'd go with erosion/piping of the softer weathered rock.
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August West
Trad climber
Where the wind blows strange
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Mar 12, 2017 - 11:20pm PT
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Drought?
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healyje
Trad climber
Portland, Oregon
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Mar 12, 2017 - 11:27pm PT
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The drill hole logs showed that the rook is fractured, and excavations up to 70 feet are required in places to reach sound rock.
It's obvious they decided to ignore this reality and just laid the thing on the dirt - er, weathered rock - instead of digging down to solid rock and building it back up right. Cheap bastards - would have cost nothing to do it right back when they built it, now it's going to cost some serious coin.
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