AP Exclusive: If [Oroville] California dam failed, people likely stuck

SF Gate ^ | February 17, 2017 | Ellen Knickmeyer

[sevinufnine]

Communities just downstream of California's Lake Oroville dam would not receive adequate warning or time for evacuations if the 770-foot-tall dam itself — rather than its spillways — were to abruptly fail, the state water agency that operates the nation's tallest dam repeatedly advised federal regulators a half-decade ago.

The state Department of Water Resources informed federal dam regulators that local emergency officials "do not believe there is enough time to perform evacuations in the communities immediately downstream of the dam during a sudden failure," according to a Feb. 8, 2011, letter reviewed by The Associated Press.

Absent "significant" advance warning, emergency responders instead would likely withdraw to safer ground and prepare for victims, said the same letter by the Federal Energy Regulatory Commission, which oversees safety of hydroelectric dams, in a summary of the state's conclusions.

[polymuser]

Spillway Failures Are How Many Earthen Dams Fail! Update On Oroville. Water Level Dropping. ..

https://www.youtube.com/watch?v=BN4bN2ixjpA

[polymuser]

Oroville Dam Rapidly Goes From Bad to Worse ...

https://www.youtube.com/watch?v=vnH6ePmJOis

[roadcat]

Looks like a cavern going back UP hill under the shorn off portion of the spillway.

In that hole in the main spillway, it looks to me that the rocky portion is not bedrock, but is comprised of boulders and rocks tossed in with a slurry of concrete poured on top, from a previous patch several years ago. The hole opened up in 2013. During this winter's storms, the water chewed up hillside behind that patch under the spillway. That's how it appears to me, that the temporary patch helped divert water backwards up under the concrete spillway. Very bad hole, should have been properly fixed several years ago. This is all Gov Brown's fault.

[polymuser]

Look at 1:29 in the 2nd video to see progression of main spillway erosion. Original square failure on lower right is still there. It is eroding upward, toward the dam, with more side earth erosion as well. This is a slow motion train wreck, imo.

And Cali wants to go single payer for to provide health care to trespassers. The stupidity in Cali is outrageous.

[Nifster]

They don’t do sirens

[TXnMA]

"I looked and see they still have not paid any attention to the parking lot side of that spillway. Thats where it will breach if it does."

Right on!

Construction of that parking lot for boat ramps -- and the idiotic rock-based road (aka dam) literally directly across the spillway for access to it -- was some of the stupidest "enginering" I have ever seen.

They took a questionable spillway design and turned it into a guaranteed disaster. And, -- as you mentioned -- the "repair" efforts so far have ignored the designed-in vulnerabilities on the parking lot end of the spillway -- and have made the problems they're trying to fix even worse -- if water ever goes over that spillway again.

Sheer idiocy! (I'm considering posting an illustrated thread on that subject...)

[crz]

Not only that, the people who engineered this spillway have no clue about hydraulics. There appears to be a hill right in front of that spillway. Now that hill is a restriction and water, like electricity, will follow the path of least resistance.

So, if you watch the video of the last overflow of that spillway, you can see that they have a lot of that water flowing back towards the main dam and then out away. Instead, when they built that spillway, ALL that hill should have been removed, an apron built from the base of the spillway the entire lenght of it, and away from the dam for some distance. I would say about 4 to 500 feet or more. That way, the water coming over that spillway would spread out gently and run away from the dam where it could have been diverted into the river channel below. Then, the base of that spillway has NO GENTLE slope. They have about a 90 degree angle where the water comes directly over the spillway and is allowed to cut at the base of the spillway. A CURVED SLOPE should have been built there to shoot that water away from the spillway. The parking lot area of that dam should have been built up at least 20 feet-a berm of sorts, to coax that water over the spillway.

When this is over, they should break out ALL the old part of the primary discharge that is damaged, including the rock which should be used to shore up around the exsisiting primary undamaged discarge area-where it now ends, and then clear ANYTHING that would restrict water flow from the end of that primary discharge. Then do the above repairs to the EM spillway.

BTW, I have a degree in engineering for marine diesel, which required us to figure forces and restriction of the power of water (hydraulics) on ships and etc.

[upcountryhorseman]

Keep in mind that the Oroville Dam is an earthen dam!

[Ozark Tom]

Saw reporting today discussing cavitation as one culprit in spillway concrete damage events with other dams. The fix has not been applied to the Oroville dam.

[TXnMA]

That hole is in the Main Spillway, and, as shown below, is far down the slope , and is separated from the dam by a ridge of bedrock:

Yes, it did break through the right side, (as viewed from below) and has created a new drainage channel that now carries almost half of the flow:

The hole's perturbation of the flow also creates dramatic spray, which can be visually confusing.

However,ever since the imminent failure of the "emergency" spillway [red dirt area at upper left] was identified, the Main Spillway (even with that hole in it) has been used to discharge water continually -- at rates at least up to 100,000CFS -- and it is still working.

Using that (damaged) Main Spillway is what made it possible to lower the water level to stop flow over the critically-damaged emergency [aka "auxiliary"] spillway. Its use has also enabled dam managers to draw the lake level down significantly -- to provide (some) room for water from the anticipated rains.

Granted, that hole is ugly, but it is not critical damage. That Main Spillway [albeit damaged] has averted disaster and allowed folks to return to their homes.

Bottom line: you are concerned about the wrong spillway...

[SE Mom]

I like this graphic, really helps to understand the threat of erosion.