Oroville Spillway is failing with enough rain dam may break - Page 3 - Mountain Buzz
 

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Old 02-13-2017   #21
 
cedar city, Utah
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Talking about '82-'83, the "8 station index" is showing moisture content is easily on a path to beat that season. They are forcast to get another 4-6" of rain in the storm starting Wednesday night. With saturated soils all of that is heading to Oroville. There is no way they make meaningful headway on repairs to the emergency spillway in 48 hours.

The damage to the main spillway is continuing to undercut earth closer to the concrete dam. How much damage will it take to it or the emergency spillway to compromise the concrete structures in place? I can't imagine the number crunching going on right now to evaluate the integrity of this behemoth structure.

And to top it off, if they keep it mostly intact, the state and agencies are likely facing serious questions given the promises they made a decade ago about the integrity of the spillway structures. They were challenged to reinforce it for ba scenario exactly like this and claimed it was fine.

Epically scary when you start hearing the word liquefaction on the news.

Phillip
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Old 02-13-2017   #22
 
San Jose, CA, California
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Below is my take based on current data, which suggest a more positive outlook.

Discussion welcome.



Thanks,

~ B
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Old 02-13-2017   #23
 
cedar city, Utah
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Thanks for sharing.

Definitely seems likely, given those forecast flows, that they can get the reservoir lower. The engineering chatter i hear is definitely worst case given the number of uncertainties in weather forecasts.

When is the historic peak inflow for Oroville?

The part i don't have the skill to vet is the structural implications if the emergency spillway fails. Does that have any effect on the primary spillway's integrity and eventually the dam (mostly the earthen support? While it seems they can probably avoid worst case for now it seems like the issue could haunt them for weeks to months through the primary melt (depending on answer to earlier question).
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Old 02-13-2017   #24
 
cedar city, Utah
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Side note, as someone buying their first home in FEMA designated flood zone, i sure hope most of those folks downstream already had policies. There is a 30-day delay on coverage through the FEMA sponsored system. And i have to wonder if they will even offer new policies in the middle of a designated state of emergency.
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Old 02-13-2017   #25
 
cedar city, Utah
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Photo of some of the damage to emergency spillway found today.
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Old 02-13-2017   #26
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Cost Control Cavitated Environmental Groups' Crest Control Critique

Oroville Dam: Feds and state officials ignored warnings 12 years ago

Three environmental groups — the Friends of the River, the Sierra Club and the South Yuba Citizens League — filed a motion with the federal government on Oct. 17, 2005, as part of Oroville Dam’s relicensing process, urging federal officials to require that the dam’s emergency spillway be armored with concrete, rather than remain as an earthen hillside.


The groups filed the motion with FERC, the Federal Energy Regulatory Commission. They said that the dam, built and owned by the state of California, and finished in 1968, did not meet modern safety standards because in the event of extreme rain and flooding, fast-rising water would overwhelm the main concrete spillway, then flow down the emergency spillway, and that could cause heavy erosion that would create flooding for communities downstream, but also could cause a failure, known as “loss of crest control.”

“A loss of crest control could not only cause additional damage to project lands and facilities but also cause damages and threaten lives in the protected floodplain downstream,” the groups wrote.

FERC rejected that request, however, after the state Department of Water Resources, and the water agencies that would likely have had to pay the bill for the upgrades, said they were unnecessary. Those agencies included the Metropolitan Water District of Southern California, which provides water to 19 million people in Los Angeles, San Diego and other areas, along with the State Water Contractors, an association of 27 agencies that buy water from the state of California through the State Water Project. The association includes the Metropolitan Water District, Kern County Water Agency, the Santa Clara Valley Water District and the Alameda County Water District.


Federal officials at the time said that the emergency spillway was designed to handle 350,000 cubic feet per second and the concerns were overblown.
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Old 02-13-2017   #27
 
cedar city, Utah
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This is the best video I have seen of the damage to the emergency spillway. And this was after less than a days worth of flow.

https://mobile.twitter.com/Cal_OES/s...885952/video/1
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Old 02-13-2017   #28
 
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Hi,

It's the erosion at the bottom right in the picture of the emergency spillway that ought to be most worrisome.

If that continues to cut back and undercuts the concrete apron -- and they can't release fast enough from the other damaged spillway -- then the next thing to stop the flow in that location will be bedrock.

I'm amazed they are not reinforcing that area. Or maybe they are, and the photos just haven't been showing it.

FWIW.

Rich Phillips
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Old 02-13-2017   #29
 
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Rich, yes, that's my understanding. Once the Emergency spillway starts to erode, they estimate that it could downcut about 30 feet into the rock. If this happened, then the entire top 30 feet of the reservoir would be released in very short order as the water rushing through tore out the concrete apron and began scouring and plucking the fractured metamorphic rock.

Here's my back of the envelope calculation:

I just looked up that the reservoir has a surface area of 15,500 acrea
Assuming the emergency spillway were downcut by 30 feet, the volume released would be about 465,000 acre-feet
If that volume were released evenly over one day (big assumption), this would equate to a flow of 235,000 cfs. This is over twice the outflow they're trying to release down the main spillway.

It's pretty likely that there would be a catastrophic failure and the majority of the water would be released within a shorter period. For perspective, if it all went evenly in a 12-hour period, that would be 470,000 cfs.

Holy shit.

Here's a good blog that I've been following as these storms have been coming ashore. He gets into the FERC relicensing issue also.

Geotripper - Liveblogging the Deluge This is written by a geologist, so you know it's spot on!
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Old 02-13-2017   #30
 
cedar city, Utah
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They are dropping bags full of boulders from helicopters into those erosion caused gullies. Hard to believe that is anything other than a desperate stop gap. Considering the next storm is now less than 48 hours away I doubt there are any other options.

Curious, on the main spillway they built up features to diffuse the power of the water before it hits the river. But the emergency feature is a straight drop ( i have heard 30') right into the base of the concrete foundation. Why vertical?

Thx for the blog, Andy. Will dive into it.
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