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Oroville Spillway is failing with enough rain dam may break

12K views 36 replies 18 participants last post by  Andy H. 
#1 ·

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#3 · (Edited)
Man, I hope that spillway's underlain by bedrock! Better call for some RediMix, guys....
 
#5 ·
I think Andy has it right. Not unusual to have serious erosion / damage on emergency spillways during high flow events. Saylorville 2010, and even Glen Canyon in 83 are good examples. Looks scary but what is important is that there is good bedrock structure below the spillway that will limit undermining the dam. My experience is that there generally is but guess time will tell
 
#6 ·
There's a dusty old geotech report that just got pulled off the shelf and is the subject of a great deal of attention right now.

OK, Bonus for the day - I went looking for the passage in Cadillac Desert describing when Glen Canyon Dam's spillway chutes were eroded out in '83, "the put-put of the Briggs and Stratton mowing the lush lawn over the turbine rooms..." and found this instead. Go to the Youtube site and there's a bunch more.

Enjoy!

Cadillac Desert
 
#7 ·
Wow. Watching the West cycle through decades of drought and now epic snowpack is wild. I am betting the political debate over water allotment the next few years in Cental Cali will be as turbulent as that spillway video.

Why are spillways so prone to this sort of damage? Isn't their primary purpose to be used in moments like this, ie shouldn't design incorporate these types of forces? Or are they assumed to perform well enough and repairs just assumed to be part and parcel?
 
#13 ·
Why are spillways so prone to this sort of damage? Isn't their primary purpose to be used in moments like this, ie shouldn't design incorporate these types of forces? Or are they assumed to perform well enough and repairs just assumed to be part and parcel?
Cavitation is a likely cause for these types of failures. A lot of these large dams were designed and constructed back in the 1950s or 60s or earlier, before engineers had a good understanding of cavitation and how to prevent it. Spillways can probably be retrofitted to prevent this, but it requires some infrastructure spending. Spending on such infrastructure has largely dwindled since these dams were built. For what money is spent on dam upgrades, my guess is that the Army Corps and other agencies that manage dams prioritize their projects based on risk. Overall, Army Corps is addressing some serious risks (e.g. seismic, flood, stability, etc.) at other dams and I don't know where spillways fall in the priority list.
 
#10 ·
Oroville Dam Spillway breach

With all the attention Oroville Dam is getting, here is some helpful information. The dam is offset from the spillway which runs down a natural hillside. Even the alternate spillway is far away from the dam itself. Here is a link to a descriptive picture.
Spillway crumbling but flows resume as DWR balances flood threat
 

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#15 ·
They are saying the Emergency spillway is on the brink of failing. Its not the main one shown in the pictures above. The report I read says they are gonna put more water down the main spillway so that less goes down the emergency one but its still pretty tenuous. Damage to the main spillway is still a worry and with more water will be accelerated.

It will be interesting to see what happens with it. I'm glad they are evacuating so that less people are at risk if/when it fails.
 
#18 ·
I hope any MB folks in the area are safe. Its tough to know how timely the news alerts remain but it sounds like the evacuation orders are creating some chaos.

They are saying 100,000 cfs is going down the main spillway. Sounds like they are trying to shore up the breaches on the emergency spillway.

Sounds absolutely frightening.

Phillip
 
#21 ·
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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#23 ·
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).
 
#24 ·
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.
 
#26 ·
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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