Evacuation orders issued for low levels of Oroville

[WildaBeast]

An evacuation has been ordered for low-lying levels of Oroville and several areas downstream from Lake Oroville, the Butte County Sheriff's Office said...

The sheriff's office posted the following on it's Facebook page:

"A hazardous situation is developing with the Oroville Dam auxiliary spillway. Operation of the auxiliary spillway has lead to severe erosion that could lead to a failure of the structure. Failure of the auxiliary spillway structure will result in an uncontrolled release of flood waters from Lake Oroville.

"In response to this developing situation, DWR is increasing water releases to 100,000 cubic feet per second.

http://www.kcra.com/article/evacuati...oville/8735215

I'm not that close to Oroville, so I'm not in any danger, but still this is kind of scary.

[Beachlife!]

That's a pretty series damn they have there too.

[crocoduck_hunter]

It's a big dam problem.

Seriously, though, that's actually pretty scary.

[WildaBeast]

The reporter on the local news (they preempted the regular programming) keeps mentioning that "this is a fluid situation". Yes, it literally is.

It sounds like the situation is improving, though. The water level has dropped enough that water is no longer flowing over the auxiliary spillway. They are instead letting more water flow over the main spillway, which was also damaged earlier this week (which is why they were using the auxiliary spillway in the first place), but they decided to sacrifice the main spillway to prevent a worse situation. Evacuation order is still in effect, though.

[Richard W]

I couldn't parse the headline at all. I was reading it as "Evacuation orders issued after low levels of Oroville were detected in California"... A bit like if Slough started to spread, or something...

[Gutter Monkey]

Originally Posted by Richard W

I couldn't parse the headline at all. I was reading it as "Evacuation orders issued after low levels of Oroville were detected in California"... A bit like if Slough started to spread, or something...

Maybe their Orgone levels are low and the headline got autocorrected?

No but really this is some scary stuff

[Kermor]

Better safe than sorry. Else, you could have another Vajont dam disaster on your hands.

[Richard W]

Originally Posted by Gutter Monkey

No but really this is some scary stuff

Yes, I've watched the video now and that really does look as though it's about to go, doesn't it?

[Lainie]

The hole scoured in the spillway was pretty impressive.

[TallGeekyGirl]

Even if the dam doesn't breach, this is bad. It's probably going to have to be demolished and rebuilt, because with the damage done can it even be just repaired? The reservoir will have to be drained for quite some time, which is exactly what drought-starved California does NOT need right now.

[Lainie]

Is there something you've read that makes you think they'll need to empty the reservoir or demolish the dam? I'm not getting that from the OP article, although it does say that the lower the water level, the less pressure there is on the spillway and the easier it is to repair.

ETA: According to this article, officials have stated that the dam itself is structurally sound.

[Seaboe Muffinchucker]

About eight years ago, there was a local dam in danger of breaching, the Howard A. Hanson dam. The situation took a couple years to stabilize.

Seaboe

[Lainie]

For decades, Ohio's Department of Natural Resources allowed "the back side" of the earthen dam that created Buckeye Lake to be excavated for construction of docks and houses (little known fact: apparently structural integrity is only important re: "the front side" of an earthen dam ).

Shockingly, this did not turn out well.

The reconstruction program is going well and ahead of schedule, apparently.

[WildaBeast]

Originally Posted by Lainie

ETA: According to this article, officials have stated that the dam itself is structurally sound.

Yes, everything I've heard has emphasized that the dam itself is not compromised. The complete chain of events for those who weren't following the story went like this: Last week damage was discovered in the main concrete spillway. Engineers cut off the flow of water through that spillway to inspect the damage and to prevent further damage. This caused water to flow over the auxiliary spillway, which I've also heard called the emergency spillway. The auxiliary spillway is really just water flowing over a concrete weir and then down a muddy hillside into the river. It theory it should have been able to handle that much water, but because of their emergency nature these things aren't able to be tested, and the flow resulted in severe erosion on the emergency spillway. Had the erosion continued it would have resulted in large amounts of water being released (but not failure of the dam itself). To prevent this, officials sent water back down the already damaged main spillway. This will likely cause further damage to the spillway, but it is the least bad option right now.

[Gutter Monkey]

Originally Posted by WildaBeast

Yes, everything I've heard has emphasized that the dam itself is not compromised. The complete chain of events for those who weren't following the story went like this: Last week damage was discovered in the main concrete spillway. Engineers cut off the flow of water through that spillway to inspect the damage and to prevent further damage. This caused water to flow over the auxiliary spillway, which I've also heard called the emergency spillway. The auxiliary spillway is really just water flowing over a concrete weir and then down a muddy hillside into the river. It theory it should have been able to handle that much water, but because of their emergency nature these things aren't able to be tested, and the flow resulted in severe erosion on the emergency spillway. Had the erosion continued it would have resulted in large amounts of water being released (but not failure of the dam itself). To prevent this, officials sent water back down the already damaged main spillway. This will likely cause further damage to the spillway, but it is the least bad option right now.

Also the auxiliary/emergency spillway is built over bedrock so even if they kept releasing water that way it'd only erode part way. However, the bedrock might be about 20 feet below the lip of the spillway and if you imagine how much water is in the top 20 feet of the lake behind the dam that's scary enough for them to issue evacuation orders for the nearby towns.

Also if the spillway starts eroding significantly there's a chance that the rest of the earthworks towards the dam face may also erode, which might cause damage to the dam if it continued.

[WildaBeast]

Originally Posted by Gutter Monkey

Also the auxiliary/emergency spillway is built over bedrock so even if they kept releasing water that way it'd only erode part way. However, the bedrock might be about 20 feet below the lip of the spillway and if you imagine how much water is in the top 20 feet of the lake behind the dam that's scary enough for them to issue evacuation orders for the nearby towns.

Also if the spillway starts eroding significantly there's a chance that the rest of the earthworks towards the dam face may also erode, which might cause damage to the dam if it continued.

From what I heard this morning, that's pretty much what the danger was. The spillway was eroding down to the bottom of the weir, which if I understand correctly could have allowed water to pass around the weir, which would have released the top 20 feet of so of the lake in a relatively uncontrolled way.

[Seaboe Muffinchucker]

So of course, the Seattle Times had to play "our dams are worse than your dams."

When dams failed and wiped out a Washington state town--twice in 15 years.

Seaboe

[jimmy101_again]

Originally Posted by WildaBeast

Yes, everything I've heard has emphasized that the dam itself is not compromised.

But I think it is reasonable to assume that since the engineers had no idea that the two spillways would develop problems then their ability to accurately predict the robustness of the rest of the dam might be suspect.

[Psihala]

An amateur YouTube Journalist gives an update on the progress of Oroville Dam spillway.



~Psihala

[Psihala]

The latest update from Oroville.



~Psihala