deirdre
Senior Member
i thought it was horrible information wise. but we know the 'hole' is near the spillway. still dont know what they are planning on doing about it and when.
Oroville Dam Spillway Failure
- Thread starter Mick West
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EricL
Member
Good example, Mick, especially since I do some whitewater paddling myself (in canoes). I could see that the deeper holes had been cut by that very process. Anyway, I thought the terminology was worth mentioning since yet another poster mentioned that one of the more common causes of levee failure is "boils", in that case, being exactly the process I described, not that which you believe was actually meant in this case.
MortarBoarder
Member
No. The powerplant is shut down. They're getting incoming power through another line... and thanks to Google Streetview, I see that it's coming in on the other side of the river.
I think the powerhouse is on the other side of the dam (see that bunch of asphalt at the base of the dam -- zoom in aerial view and you'll see that is where the gear is for feeding power to the outgoing lines). "Oro Powerhouse Road" ends at "Oroville Dam Blvd E". On Streetview, go east on the Blvd a couple of bends and you'll see a small power line leaving the road and going off toward the powerhouse. That's probably the incoming power line, and it's not going over the threatened ridge.
Vicki W
New Member
Fair point. I should have said they are speaking to each other and seem to be coordinated. Frustrating for data types, but see my comment about "delta" being used instead of net change during the press conference. They have a hard time communicating technical information to the lay public. Perhaps they should take media communication classes.
It probably will, although you will note the Bullard Bar spillway has a reinforced ramp at the bottom (halfway down the hill) which prevents local erosion by shooting the water out horizontally and up a bit. Oroville obviously lacks this, as it's just got a big hole, so erosion will occur regardless - just hopefully very slowly once it gets to rock.
deirdre
Senior Member
well the media didnt ask them either
but yes it all seems to be very coordinated and moving along.The helicopter flyaround throughout the press conference was really helpful in this regard. There is a hole beneath the auxiliary spillway and one could already see that the top part has started being filled with rocks.
Update: Not so sure about this anymore. Watching the footage again it seems like the rocks and boulders right beneath the right most side of the auxiliary spillway have already been there as part of the original construction.
They obviously have created a working infrastructure: Bringing in rocks from a local quarry (?), unloading them on a large asphalt area next to the dam. In this area you could see excavators, dozers, dumpers at work, sorting, piling and loading the various sizes of rocks into huge plastic bags and two helicopters to transport these to the site.
Update: There is no infrastructure in place at the hole that would make a placement of the quarry material possible in some kind of fashion resembling a construction site. Instead they probably plan to just dump the 1 ton bags right into the hole as a desperate interim measure in case of another overflow later in the season.
Kudos to whoever put the logistics of all this in place.
And Kudos to this site! The knowledge and willingness to discuss and analyze in a most civilzed way is just stunning!
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MortarBoarder
Member
The auxiliary/emergency spillway doesn't have any concrete below the smooth concrete lip and its foundation. The water flows smoothly over the top of that wall, flows down the face, hits rock at the bottom and flows across the hillside's dirt and rock (and trees and bushes and earthworms). There is nothing added to keep it from the main spillway because there's a ridge of rock between the two spillways.
Levee boils (a very different thing to a whitewater boil) are a cause of failure of levees,
But that's obviously not happening here. Otherwise the emergency spillway would have failed by now.
deirdre
Senior Member
thank you i didnt see that, and didnt look for footage as i assumed media copters would have to stay away with all the helicopter work going on. will go check it now.
It seems like the 50 foot drop is wishful thinking. The storage at 50 feet from the spillway top, or 851 ft, is about 2,822,000 AF. That is 646,000 AF lower than the current level. If the storm comes in as expected, there is at most 60 hours before the flow starts ramping up, which would mean net outflows of 10,767 AF/hour or 130,277 cfs
deirdre
Senior Member
i think she means why are there no concrete blocks against the 'weir' near the main spillway, and why no fill in there. so the water doesnt fall as far over the lip.
EricL
Member
Yes, my point exactly, even if I might have been more descriptive than necessary (I have a tendency to be thorough).Levee boils (a very different thing to a whitewater boil) are a cause of failure of levees,
But that's obviously not happening here. Otherwise the emergency spillway would have failed by now.
Pictures are helpful there
MortarBoarder
Member
The rock of that mountain is metamorphic and mostly igneous in origin. Metamorphic means it's been altered, so it's not like the solid mass of rock as you imagine for Rio's Sugar Loaf. At least it's not a conglomerate, so it is not necessarily made of glued-together bits. However, it has been described as a "hard" rock. And it's up to 1500 yards deep, while the reservoir is only 300 yards deep.
So the waterfall at the bottom of the broken spillway will wash away pieces of a "hard" rock where it finds weakness, but there is not a soft rock which can undermine the harder rock. I think there are still hundreds of yards of concrete spillway remaining, and the water will have to chew through the edge of the concrete and find enough weaknesses in the supporting rock before it can progress further. I suspect that the weakness may be where the concrete was laid on soil/gravel rather than bedrock... We can see photos of the intake valves being mounted on carved bedrock, but we don't know how far down the spillway is resting on bedrock.
Vicki W
New Member
I'm speaking of the concrete coping that abutts the bottom of the concrete rollover of the auxiliary spillway that can be seen pictured here. There is a small portion to the right closest to the main spillway with what looks like erosive damage even prior to this event (according to this google earth image) and that seems to be the area that sustained the most damage (the hole or boil depending on what people are calling it. I think of a boil as a continuously upwelling that would still be ongoing, but I could see how the rafting definition could confuse the semantics).
EricL
Member
All good points in the rest of your post, but I thought I'd address this part. Metamorphic rock is not, in any general terms, necessarily softer than igneous or whatever other type it originated from. It can even be harder. For example, in one local area where I live we have a form a quartzite (a metamorphic rock) which is extremely hard and durable, some of the hardest rock I've seen. One needs to know more than just the class of rock to make a guess as to how durable it might be.
deirdre
Senior Member
TOTAL guess here... im thinking its like a rain gutter, designed to move the water (although i cant really envision how it would, towards the pit because the pit is where the overflow tube is installed that goes under the road?
In case of a total fail of the damaged spillway, 'unconventional solutions' to get the water down in the river are needed. Perhaps even soon, in case the dam will be in direct danger. Unconventional solutions like: a bunch of siphons over the emergency spillway to the river. Size pipeline, like they use on sea (big rolls of them). No idea about the technical problems this would face. Just an idea to start a brainstorming. Or, the drilling of one or more big holes in the emergency spillway for a more controlled outflow of water.
I am not sure whether the spillway still can be used the next months. Perhaps not even weeks. New ideas will take time to implement. A bit of early brainstorming can help
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EricL
Member
The spot you speak of looks to me like it could possibly be a remnant of the original topography of the valley wall. Note that in light of Vicky's comments below, you can see that a much larger area along the natural flow path looks like original topography from before the time the dam was built. If not that, it could be intentional landscaping for funneling the flow of water toward that side (note that the roadway tends to make that happen, and surely the designers knew it at the time), and though that seems like a bad idea when considering the severe flow already seen here, perhaps they never expected the spillway to be over-topped by more than an inch or two. It has been mentioned numerous places that the emergency spillway has never been over-topped before, so I'm sure what's seen in that image is not post-construction erosion.
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Vicki W
New Member
Is there a system like that in place? I could see that if there was. It would also make sense with the topography, but it wouldn't necessarily make sense in terms of protecting the main spillway, as it angles towards it.
I found it interesting that in the Google earth image from before this all happened, it appears that this little section looked to have erosive changes or a tendency to pool water.
In fact, if you back out on the image on Google earth, you can actually see channeling from prior rainfall.
MortarBoarder
Member
Frankly, I'm sure that the designers of the emergency/auxiliary overflow knew what they were doing. This overflow is so far below the top of the dam that it was expected to be able to handle several feet of water over the top. That's a lot of force. The only reason for there to not be any spillway built at the bottom of that vertical concrete wall would be because what we see is expected to be able to handle that force.
So, if we assume that the engineers were competent, that simple concrete wall should be anchored solidly to the bedrock and the water can't undercut it.
The present engineers can't trust that is the case, because the dangers of a failure are very large and are on their shoulders. So probably what will happen is they'll continue trying to lower the level -- they've already resigned themselves to having to later rebuild the concrete spillway. If the situation remains stable, they'll lower the water so they can thoroughly reexamine both sides of the auxiliary spillway and do whatever it takes to assure themselves that it can be used. Even if it's not necessary, there will at least be a short concrete apron added below that spillway.
deirdre
Senior Member
the red arrow in my pic is actually a flowing water stream from an overflow tube under the road. as far as if the 'rain gutter' theory is correct, i have no idea. They are saying the side of the main spillway there is solid bedrock, so it kinda is protected from pools i'm thinking.
Scott Gates
Active Member
For what it's worth here's what it looked like when the lake was lower. It just looks like a retaining wall.
Perhaps it was never meant to stand up to being topped for days on end and the original designers knew it would blow out. Perhaps it's better just to think of the whole area as the emergency spillway. Just a sacrifice zone to protect the dam proper in the last extreme.
A better view - this is the question area I think is being asked about ... there is a concrete pad the laminar flow along the weir hits for most of the wall - but none apparent at the area closer to the main spillway:
I would be pretty certain there is a similar blocking under this section ... however, during the period while they were clearing the hill in prep for the emergency spillways possible use, they brought in large boulders and cemented them ...
This hardened area performed well ...
And today they are extending that area even further ...
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skicopper
New Member
Hello everyone, I've been monitoring this for the past 24 hours and there is a lot of good information here. Great job Mick! Does anyone know if there is some sort of 'controlled release plan' written by the original engineers that is available to the public? I feel like the designers of the dam may have intended that "emergency" spillway to be used in some sort of completely uncontrolled scenario like an apocalyptic type of event. And I don't mean zombies, but a true "end of world" scenario like an invasion by another country where everyone had evacuated and no one was there to monitor the dam. The engineers probably knew that at some point it would fail but at the very worst it would send a 30ft wall of water and save the dam from over-topping. I just don't think the emergency spillway was ever intended to be used as part of a controlled release.
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EricL
Member
I would question that logic only because we've already seen holes eroded 20 to 30 feet deep, even within roughly 50 to 60 feet of the base of that spillway. You could be right, in the event that the spillway structure is actually embedded that deeply (or more) within the ground, but based on the presence of that little deflection lip along the "left" three-quarters or so of the structure, I tend to think it's not founded that deeply. In addition, the way in which that deflection lip rises and dips according to the existing grade is almost a sure sign that the spillway is founded just below the existing grade. Had they founded it deeper, backfill along the bottom side would have been placed to a more constant elevation and the deflection lip would be level, or at least having constant slope.
Surely there's someone alive who would know the depth of bearing, and drawings ought to still be available in some form. If they really don't have that information, you can bet they'll be digging test pits in the next few days to find out.
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Vicki W
New Member
Good point about natural topography. I also wondered if it could be from natural rainfall as it runs off the concrete of the spillway? (so not from spill over, but just run off).
I agree that this seems like knowable information, but not sure we have access to the info.
deirdre
Senior Member
not with that amount of water coming. they get washed away then jam up the river.
EricL
Member
My understanding is that the trees likely would have ended up in the river downstream, complicating the danger of already-high water.
Recent flow data has missing information for inflow. The inflow can be inferred by regressing the delta in elevation change to previous data that reports both discharge and inflow. Current delta in elevation is -0.35 feet/hour, and based on the regression this indicates that flow balance is -60,000 cfs. Reported discharge is 100,000 cfs, which support an inflow of 40,000. This appears to be high when compared to the recent recession curve (which is below 35,000 cfs). This substantial discrepancy may be due to a prism in elevation across the lake that is settling to a flatter surface over time.
EricL
Member
I thought it best to add something to my previous reply. You imply that whatever the elevation difference is between the top of the primary dam and the top of the emergency spillway must be the equal to the depth (thickness) of flowing water over that spillway lip that the engineers were expecting. That's almost certainly not the case. Much of the strength of the soil structure within the dam itself comes about due to the confining force exerted by the weight of the fill above. At most elevations within the dam, that happens automatically, but at the very top of the dam, there is no such confining force because there is no additional material above that point. Thus, I would expect the portion of the dam which matches the highest design water level to have a substantial thickness of fill above it, contributing to the necessary strength of that material. Providing several feet of fill above the maximum waterline would only make sense, and I think it very unlikely that the design maximum pool elevation was intended to be near that of the top of the dam itself. That's just my logic and experience, but I could be wrong. This is an idea which could easily be checked, if one knew where to look.
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Okay, it looks like I stand corrected on this one!! No one has specifically said addressed what I wrote, but it's been mentioned in some of the more-recent posts that job specifications stated that the emergency spillway was intended to operate with the water being several feet above the top of the lip. On that same note, severe damage to the spillway during such a scenario was to be expected and considered acceptable. I guess that still shoots down the idea that the substrate was expected to hold up well, but still, it's hard to imagine that that was the standard of the day. Wow.
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Scott Gates
Active Member
What appears to be a significant contributor to the erosion areas - especially regarding the erosion at the left end of the downstream side of the weir ... is the "stepped" heights and the resulting side slopes that directed water laterally across the flow off the weir, rather than straight downhill. Additionally the change between the weir and the buried spillway top along the parking lot also created and additional concentrated lateral flow.
You can see this here:
And the problem area erosion largely matches where these lateral flows meet the downhill flow off the weir and concentrate ...
More detail:
You can see this here:
And the problem area erosion largely matches where these lateral flows meet the downhill flow off the weir and concentrate ...
More detail:
Scott Gates
Active Member
That is quite a bit out of context. The only reason it seems so deep is because it is cutting thru the raised roadbed.
A view from above with context ... the flat area from the "cut" at the road back to the spillway is the reinforced, cement and rock hardened area - which you can see to the left of picture ... which is being extended as we speak.
The erosion at the other end seems far more of a concern as it was much closer to the weir wall ...
Note there's a few "holes" - (deep erosion pockets near the weir at the wop of the emergency spillway). The one above is where the road was cut through. Here's it forming. I'm pretty sure this is what is meant by a "boil" here - i.e. the whitewater usage:
This one:
is a different hole, not as deep, but much closer to the dam. Again, it just looks like erosion, and not any kind of upwelling.
The Lake Oroville web cam gives a live look at the level of the lake:
https://www.parks.ca.gov/?page_id=29411
Looks around 6 feet compared with the van on the left. Matches 15:00 figure of 894.88
https://www.parks.ca.gov/?page_id=29411
Looks around 6 feet compared with the van on the left. Matches 15:00 figure of 894.88
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