Prayers for members Harvey and Al Weidman., The Oroville Dam E-Spillway is failing. Options

[ConeDodger]

Heard from Harvey this AM. His house is at 180', his shop at 87'. They evacuated to their cabin which is much higher as the recommended evacuation was 200' and lower. He's back but has been told to be evacuation alert.

So, all is well as of now. (IMG:style_emoticons/default/cheer.gif)

[Spoke]

Good luck guys; hope all stays safe.

That dam looks mighty scary being as high and full as it is. Plus it's an earthen dam?

Question:

What is the purpose of this dam? Flood control? Water supply? Power?

[Cracker]

Water supply and power for sure...possibly flood control too.

T

What is the purpose of this dam? Flood control? Water supply? Power?

[AZBanks]

Praying we don't have a repeat of the Teton dam disaster.

http://www.history.com/topics/us-states/id...sters-teton-dam

[GregAmy]

What is the purpose of this dam? Flood control? Water supply? Power?

All of the above.

Note that the 770' dam itself is not at risk; it's fine.

Haven't read the entire thread, but Saturday/Sunday's issue was a culmination of a couple of things. First, earlier failure of the downstream primary spillway (the long concrete chute) which caused them to reduce the flow through that spillway to avoid further damage. They intentionally allowed the reservoir level to rise and overtop the emergency weir for that purpose.

What they had not accounted for was the erosion below that weir. As water volume increased over the weir that area became significantly eroded and scouring below it started to walk up toward the weir. They called for immediate evacuation because they saw the scouring moving toward the weir and were concerned they could not stop the flow over it before it compromised and they lost the weir. To address that they doubled the flow through the primary spillway (that was a ballsy call) and coupled to the coincidental (and fortunate) significantly reduced flow INTO the reservoir, they stopped the flow over the weir, alleviating that immediate problem.

They are now armoring that weir overflow area with stone bags and grouting so that if the level does rise above the weir again that area will be secure. Fortunately, the primary spillway damage is stabilized at the current flow of 100k, so there's no immediate risk there either. They'll continue to run the spillway at that "known safe" flow of 100k to draw down the reservoir as much as possible as a buffer against future inflows.

So again: no danger to the primary dam, situation stabilized at the spillways, with mitigation efforts ongoing to ensure it doesn't happen again. Here's a nice link to see current flows in and out, as well as reservoir level; for reference, flow begins over the weir at 901 feet. Hit "latest" at the bottom to get updates:

http://cdec.water.ca.gov/cgi-progs/queryF?...mp;span=24hours

Not associated with the program in any way. Have some Internet-friends that are, but this info is all publicly available.

[Rand]

The dam is absolutely at risk if the erosion gets bad enough! That's the whole reason for the concern. Thankfully, it looks like that's not going to be an issue now that they've been able to get the water level down and stop the erosion. BUT, there's more rain in the forecast, so we can't assume everything is just going to be ok.

[GregAmy]

The dam is absolutely at risk if the erosion gets bad enough!

No, that's entirely wrong. The main 770' dam is not at risk in any way. In fact, if the erosion below the weir were to have continued up and completely taken it out , that would have, in fact, REDUCED the risk to the dam (that's what spillways are for). And even if the almost-entirely-impossible were to happen and both the weir and the primary spillway were completely taken out, there's no reasonable possibility that the erosion damage would migrate around that corner to the point where flows would erode the earthen dam. The most likely scenario in that case would be those spillway structures would collapse and take out that entire hillside below them down to bedrock all the way to the river (they were not even close to that scenario).

Now, if you're using the word "dam" to refer to the entire SYSTEM, then yes, each of those components is part of that "dam system". But, I'm using the word "dam" to refer to the 770' high primary structure that blocks off the main channel of the Feather River. And that structure was not, and is not, in any danger of foreseeable compromise in any way.

That's a fact, and not an alternative one. Yes, I am an engineer.

I think we'll find that this whole thing was a result of lack of imagination. When they designed this system in the 60s, they pretty much over-designed the primary spillway's capability to handle the water flows into that valley. As such they did not put as much emphasis on designing a stronger weir (which was intended only to take care of flows that the primary spillway could not.)

What I think they failed to imagine was a compromise to the primary spillway. "But for" that compromise, this would have been a non-event (combined flows have been less than what that system handled easily in the 1997 floods). That thought is supported by the last-minute scrambling to clear the hillside of potentially-clogging vegetation, grouting and rip rap below the toe of the weir and along the roadside, and surprise at the levels of erosion below the weir.

Mother Nature has little empathy for the hubris oversight of Man.

[Rand]

The experts I heard talking were saying if the erosion got deep enough it would undermine the dam itself. If that happened it would lead to failure of the actual dam.

But hey, I have no interest in arguing it. I was just sharing info. You clearly know more than I do on the subject. (IMG:style_emoticons/default/beerchug.gif)

[GregAmy]

The erosion of concern last weekend was for that area below the emergency weir, not the main 770' dam.

CA DWR has been doing an excellent job of providing up to date photos of weir damage repair:

http://pixel-ca-dwr.photoshelter.com/galle...Spillway-Damage

In the link below (not allowed to insert photo here), the area that caused the concern is the dark grey grouted area in the foreground. Look in that second "before" photo, and you can see how that was working its way up toward the weir (it's the area to the far lower left in the photo). Had that erosion made it all the way there it could have compromised and collapsed the weir. If that end of the weir let go, it may have taken the whole thing with it, and potentially continued across to take out the primary spillway. And that would have been "really bad".

They were backed into an ugly corner that evening: allow the reservoir level to increase and risk losing the weir, or increase the flows through the primary spillway to reduce the reservoir level, and risk further damage to the spillway. Someone made the (in hindsight, clearly correct) gutsy call for the second option, and the primary spillway handled the extra load just fine, allowing the reservoir level to drop below 901 (and continuing as we type).

Today:
http://pixel-ca-dwr.photoshelter.com/galle...-02-15-2017-jpg

Before:
(IMG:http://www.914world.com/bbs2/uploads_offsite/media.viafoura.net-15565-1487204451.1.jpg)

[914_teener]

Should the wier structure have failed completly all the lake water up to the main dam level level would have been drained uncontrolably into the valley. It would be pure conjecture to speculate how it would fail....eithier a point failure or all at once. I think the elevation differential is about 9 feet. Everyone at my work was talking about this today.

They did the right thing in all cases by risking further damage to the main spillway and evacuating those in danger.


As God would have it......the storms held off a week.

My prayers are still with them until the damage is repaired and we are into the dry season.

[dlkawashima]

The irony is this was predicted long ago ...

SACRAMENTO BEE: NOVEMBER 27, 2005
Oroville Dam contains a flaw, some critics assert, one that could damage the structure during a major flood
and threaten downstream communities. That flaw is the dam's emergency spillway, which empties onto a
bare dirt hillside adjacent to the earthen-fill dam. If the emergency spillway had to be used to help quickly
drain the reservoir during a major flood, the force of water rushing over the spillway lip would violently erode
the hillside, washing out roads and power lines below, according to both the critics and the state agency
that operates the dam. It also could undermine the foundation of the spillway, a potential disaster ...

[Cracker]

Anyone who could rub a few brain cells together could figure that one out. Ridiculous.

PS: Not your post...the lack of erosion control on the hillside. I couldn't believe my eyes when I saw the run-off carving up the terrain and washing out the road. Incompetence of the highest order...maybe the engineers of the day where simply masquerading as such - or slept at a Holiday Inn.

T

[quote name='dlkawashima' date='Feb 15 2017, 09:03 PM' post='2455045']
The irony is this was predicted long ago ...

[GregAmy]

PS: Not your post...the lack of erosion control on the hillside. I couldn't believe my eyes when I saw the run-off carving up the terrain and washing out the road. Incompetence of the highest order...maybe the engineers of the day where simply masquerading as such - or slept at a Holiday Inn.

I was told by "someone in the know" that all that erosion damage, such as the washing away of the parking lot road and erosion of the hillside, was "expected" and "accepted" as part of the design, presumably because it was a once-in-never probability. And I agree that anyone with reasonable engineering - and 20/20 hindsight confirmation that it will happen - looks at that and says "uuuuhhh?"

That's why I'm thinking that there was no real expectation that it was ever going to be used, so there was 'no need' to spend a lot of money on it. Except they never took into consideration the possibility of spillway failure...

Hindsight is 20/20. And those responsible for the designs and/or cost cutting will, most assuredly, be roasted on the spit of hindsight history.

[Cracker]

At one point, at the height of the lake level rising, the incoming water was multiples of the spillway's ability to discharge - even at full flow. It was, as you say in 20/20 hindsight, foolish to design such a system. The idea that it is called an "Emergency spillway" is ironic - the apparent fact they never thought it would be used is obvious - thank God no one has paid a high price. My point regarding the damaged spillway is it doesn't matter - it would of possibly been overwhelmed regardless. Fascinating and sad at the same time.

T

[SirAndy]

As God would have it......the storms held off a week.

Not to get too off topic here but i never understood this line of thinking ...

Would you also have invoked "god" if the dam/weir/spillway had failed this past weekend?
And if so, then what difference would that make either way?
And if there isn't really a difference, then why go there in the first place?
(IMG:style_emoticons/default/confused24.gif)

[Cracker]

...that can get it off topic alright - "God" talk will, correct! C'mon Andy...that's like poking someone with a sequoia - subtle it is not.

T

[SirAndy]

that's like poking someone with a sequoia

It just so happens that i have both the sequoia and the stick for poking ...
(IMG:style_emoticons/default/laugh.gif)

[Cracker]

Thank God you had that picture...hilarious! (IMG:style_emoticons/default/rolleyes.gif)

T

that's like poking someone with a sequoia

It just so happens that i have both the sequoia and the stick for poking ...
(IMG:style_emoticons/default/laugh.gif)

[mbseto]

Mother Nature has little empathy for the hubris oversight of Man.

History shows again and again how nature points out the folly of man.
https://www.youtube.com/watch?v=myqSETD5_bs

[AZBanks]

As God would have it......the storms held off a week.

Not to get too off topic here but i never understood this line of thinking ...

Would you also have invoked "god" if the dam/weir/spillway had failed this past weekend?
And if so, then what difference would that make either way?
And if there isn't really a difference, then why go there in the first place?
(IMG:style_emoticons/default/confused24.gif)

Because God is in control either way.