Oroville Dam Crisis and 200000 people evacuated.

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Huge amounts of rainfall have caused water levels to rise rapidly in the Oroville Dam, it's got to the point where yesterday the emergency spillway was used and that was eroding due to the water spilling over. The good news is that water is no longer being channelled through the emergency spillway, the bad news is that half of the main spillway has collapsed from water erosion and the current policy of lowering the dam water level at a greater rate will make the problem worse. Of course the situation is dependent on rainfall being minimal.

http://www.zerohedge.com/news/2017-02-13/oroville-dam-evacuations-here-are-latest-updates

http://www.bbc.co.uk/news/world-us-canada-38952847

I just hope the authorities have a plan because that main spillway cannot continue eroding, otherwise it will recede all the way back to the dam and compromise the structure.

For some context, the water crashing against those cliffs is part of that erosion. Two weeks ago these cliffs did not exist.

[jaredh 195]

They have a serious issue.

The emergency spillway started eroding the second water went over it (not the one pictured here).  There is a real threat that if water continues to crest the emergency spillway, the entire concrete structure that IS the emergency spillway will give way, releasing a full 30 feet of water downstream.

That's 100 feet of water in the first town.  Seriously.  The town would be under 100 feet of water...in about 20 minutes.  The town next down the river would be under 10 feet of water in an hour.

They aren't in jeopardy of losing the entire dam....but they are in jeopardy of losing 3-4 towns downstream.  The issue here is they never have allowed water to crest the emergency spillway to test its viability.  This is crazy.  The emergency spillways at every dam should always be tested once to verify the engineers built them right.  The test should be done when the lake has a controlled level so its just a short overflow of the spillway.  They did this at Hoover dam when the lake originally filled.  I really cannot fathom why this dam's emergency spillway was never allowed to top for a test.

[matias93 7,535]

I know this is not the moment to point fingers, but what surprises me is that the spillway were a concrete plank over earth, instead of the more typical free flow over rocks. I guess is because the damming point is not a natural narrowing on the river course, so all the dam is basically compressed earth, but that's precisely the risk factor: the water would eventually return to a less forced course, going through the earth and to the rocks, if there are any.

On the BBC photo you can see that the concrete is barely more than 1 metre deep:

It is simply too easy for some water to get into some crack and start eroding the spillway from the underside, and if the internal face of the dam is also just compressed earth, infiltrating waters could do most of the job.

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33 minutes ago, jaredh said:

They have a serious issue.

The emergency spillway started eroding the second water went over it (not the one pictured here).  There is a real threat that if water continues to crest the emergency spillway, the entire concrete structure that IS the emergency spillway will give way, releasing a full 30 feet of water downstream.

That's 100 feet of water in the first town.  Seriously.  The town would be under 100 feet of water...in about 20 minutes.  The town next down the river would be under 10 feet of water in an hour.

They aren't in jeopardy of losing the entire dam....but they are in jeopardy of losing 3-4 towns downstream.  The issue here is they never have allowed water to crest the emergency spillway to test its viability.  This is crazy.  The emergency spillways at every dam should always be tested once to verify the engineers built them right.  The test should be done when the lake has a controlled level so its just a short overflow of the spillway.  They did this at Hoover dam when the lake originally filled.  I really cannot fathom why this dam's emergency spillway was never allowed to top for a test.

I am waiting for daylight pictures for the main spillway as there is clearly a huge hole which is creating a waterfall effect. The water will scour out the bottom causing the parts of the spillway hanging over to eventually collapse and the process repeats. Problem is there still much inflow into the lake due to storms from last week, water cannot get above the level where the emergency spillway is

Another possible factor is liquefaction, with all the water spilling over from the main spillway, how much of it is being absorbed in the lower parts of the terrain adjacent to the spillway? If there is liquefaction then this raises the possibility of a landslide on parts of the slope very close to the main spillway- which will only take away more parts of the main spillway.

[airman15 4,113]

Evacuations are already underway for the counties in the immediate area. CNN has released photos of the water's path and the main spillway. Evacuations are urgent enough to where nearby Beale AFB is letting evacuees pass through. The National Guard is also underway to try and repair the damaged parts of the main spillway.

In a worst case scenario, the rivers will eventually flow to Sacramento and the levees will be overwhelmed. I hope that isn't the case; neither Placer County nor Sacramento County has not said anything about how we will be affected.

2 hours ago, jaredh said:

The emergency spillways at every dam should always be tested once to verify the engineers built them right.  The test should be done when the lake has a controlled level so its just a short overflow of the spillway.  They did this at Hoover dam when the lake originally filled.  I really cannot fathom why this dam's emergency spillway was never allowed to top for a test.

Just a few years ago we weren't getting any water. Folsom Lake which has it's own dams/spillway was so low that it uncovered an abandoned gold rush town and it only began to recover because only so much water was being let out. I suppose it can be argued we could have taken the time to inspect our infrastructure while the levels were down but we needed to conserve what water we had left for drinking and plumbing. Check this link to see what Folsom, and two other major reservoirs looked like between then and now

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30 minutes ago, airman15 said:

Evacuations are already underway for the counties in the immediate area. CNN has released photos of the water's path and the main spillway. Evacuations are urgent enough to where nearby Beale AFB is letting evacuees pass through. The National Guard is also underway to try and repair the damaged parts of the main spillway.

In a worst case scenario, the rivers will eventually flow to Sacramento and the levees will be overwhelmed. I hope that isn't the case; neither Placer County nor Sacramento County has not said anything about how we will be affected.

The main spillway can't be properly repaired when there is a 100000cfs going down it. From those new pictures it looks like the collapsed main spillway is getting closer to the line of those power lines. The main spillway will be useless if most of it has been eroded by the water. That's the future guarantee of the dam and the damage done to the main spill way is going to take many weeks, possibly months to repair. All of that ground washed away will have to be rebuilt and/or reinforced.

[Fantozzi 4,068]

Don't understand why erosion on the spillway can cause an evacuation of 200.000 people. If the erosion makes the dam instable - then, imho, the spillway was placed wrong. I'm no expert but I never would place a spillway in the middle of a natural damn (where the pressure of the dammed water is highest on the damn) but at the edge.

But if the spillway is placed right the erosion of the mountain side as shown in videos shouldn't be that dangerous. Looks spectacular, yes - but why it's dangerous?

In my naive opinion this means they placed the spillway at a point where it shouldn't had been placed. No?

 

 

 

 

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The fear about the emergency spillway, well the fear yesterday, was that it would take away a portion of the dam immediately next to the emergency spillway. Thus the water level would rapidly lower by maybe, I dunno, anywhere between fifty to a hundred feet?

By the looks of it the emergency spillway should send water into the main spillway. Instead a lot of the water went over and eroded the ground which is supporting the section of the dam which has the emergency spillway. My main concern though is the main spillway, the bottom half has been eroded terribly and it will have to be completely replaced. But that means extensive earthworks that will take some months (perhaps several) to ensure there is a firm foundation for the new spillway.

In the meantime the only means of lowering the water level -- if neither the main or emergency spillway can be used -- is through the turbines. But this would not do enough if there were prolonged heavy rains, storms and melting snow from the mountains. Clearly the water cannot spill over the dam since, it being an earth dam, this would rapidly erode the structure.

But using the main spillway to lower the water level is only to going to increase the long-term issues for the Oroville Dam. This erosion is causing a series of violent waterfalls to emerge in the battered and collapsed bottom half of the main spillway. Unfortunately waterfalls only move in one direction- upstream. If there is no catastrophic failure and the water levels hold through this year, then expect to see one massive gorge where was the main spillway. But there are official reports this morning saying that there has been no further deterioration of the main spillway, but I find that hard to believe. Surely the maintained high outflow of water is only going to increase erosion in the bottom half of the main spillway? Perhaps these officials meant that there was no deterioration in the top half of the main spillway?

As a long-term solution, perhaps construction of a second main spillway could make more sense as this would be quicker?

[airman15 4,113]

6 minutes ago, Ln X said:

The main spillway can't be properly repaired when there is a 100000cfs going down it. From those new pictures it looks like the collapsed main spillway is getting closer to the line of those power lines. The main spillway will be useless if most of it has been eroded by the water. That's the future guarantee of the dam and the damage done to the main spill way is going to take many weeks, possibly months to repair. All of that ground washed away will have to be rebuilt and/or reinforced.

Underway as in gathering the necessary personnel. 23,000 are being called in with 8 helicopters as per CBS. My bad for not specifying that bit. Early estimates for a full rebuild are expected to cost upwards of $200m..

 

11 minutes ago, Fantozzi said:

Don't understand why erosion on the spillway can cause an evacuation of 200.000 people. If the erosion makes the dam instable - then, imho, the spillway was placed wrong. I'm no expert but I never would place a spillway in the middle of a natural damn (where the pressure of the dammed water is highest on the damn) but at the edge.

But if the spillway is placed right the erosion of the mountain side as shown in videos shouldn't be that dangerous. Looks spectacular, yes - but why it's dangerous?

In my naive opinion this means they placed the spillway at a point where it shouldn't had been placed. No?

The dam in question is an earthen dam which faces another erosion risk. The spillway is supposed to take overflow directly to the river below. An uncontrolled flow of water down the sides and toward the dam is quite a big problem considering it's supposed to be holding back the weight of the water behind it.

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2 minutes ago, airman15 said:

Underway as in gathering the necessary personnel. 23,000 are being called in with 8 helicopters as per CBS. My bad for not specifying that bit. Early estimates for a full rebuild are expected to cost upwards of $200m..

 

The dam in question is an earthen dam which faces another erosion risk. The spillway is supposed to take overflow directly to the river below. An uncontrolled flow of water down the sides and toward the dam is quite a big problem considering it's supposed to be holding back the weight of the water behind it.

Good. I think the emergency spillway can be patched up, provided there isn't too much liquefaction. I wonder what kind of bedrock it is? If it igneous and/or metamorphic there is time to fix this, but if it is sedimentary...

I still feel though that the greatest liability of them all remains the main spillway, it is literally the Oroville Dam's lifeline when the water levels threaten to spill over the dam. Here also are some clips from AP which shows footage from today.

 

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Here is another update for today. The good news is that the road just beneath the emergency spillway has been repaired and a mixture of concrete and boulders is being placed in front of the emergency spillway. The bad news is that the erosion of the bottom half of the spillway continues unabated- not only is there the main crater but there are several areas where the concrete sides have collapsed.

 

Edit: The youtuber Alan Kuentz has good videos which show the true scale of the erosion of the emergency spillway and up-to-date ones as well.

 

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Here is another update from Alan Kuentz which shows the progress made in patching up the emergency spillway.

 

It is good to see so much material being added to the eroded gulleys close to the dam wall. My big worry though is that the heavy rains will cause further topsoil erosion and some scouring around the area of the boulders / concrete which is on the lower part of the slope. If there's less of that slope then there is less ground support for the very heavy concrete walls of the weir (the part where water was formerly spilling over last Sunday and Monday).

Worse still it's looks like there is a lot of soil and sedimentary rocks which be easily washed away with a heavy downpour. If water had not gone over the emergency spillway then there would have been virtually no erosion. But those exposed gulleys need to be filled in ASAP otherwise they will only grow with heavy rains.

[airman15 4,113]

NPR confirms evacuations lifted, but it's not yet time to be popping corks.

Besides the repairs still taking place, rains have started again. Forecasts of storms are still relevant at this time and several of the parks and houses adjacent to the river were getting the brunt of flooding. As long as the dam itself can hold which is what the source points out, then we shouldn't be facing the worst outcome.

The soil getting washed out was caused in part by the drought we faced in the last five years. Sure we may have had a shower now and then during that period; yet it wasn't enough to keep the ground from drying out. Further erosion will most certainly be a concern here, so the dam continuing to stand is the one thing we can still hope for right now.

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https://www.metabunk.org/oroville-dam-spillway-failure.t8381/page-3

This weblink gives an update to erosion around the main spillway. Now there is new erosion and another gulley forming to the right of the main spillway (facing downstream). In short the lower half of the main spillway is getting FUBARed more and more. Since the rain is intensifying, I hope this doesn't mean the erosion on the main spillway starts receding back towards the dam.

Another concern is that the main spillway flowout is now decreasing, this is due to structural and geological limitations- as the water level decreases the higher flow rates will cause erosion behind the main spillway gates, thus the flow must be decreased. I hope the engineers keep their eye on the ball and raise the flow rate as necessary when the dam water level begins rising again.