SeanT
Member
No, I was mistaken. It isn't clear from that picture where the stream starts as that's the bottom section of the broken spillway.
Oroville Dam Main Spillway Waterfall Erosion Watch
- Thread starter Mick West
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No, I was mistaken. It isn't clear from that picture where the stream starts as that's the bottom section of the broken spillway.
Paul Bogdanich
New Member
What are you basing that on?
I watched some live chopper footage from the 13th or 14th of the water coming over the last intact part of the spillway when they were still draining 100,000 cfs. The flow had taken the dirt that used to abut the concrete spillway wall back about four feet and the water was flowing over the break in the former structure. Raged concrete edges. Not smooth or tapered. No defined leading or trailing edges like the blocks in the photo you posted. Although I couldn't see any, one would assume there were also pieces of rebar or steel mesh sticking out of the concrete here and there if it was reinforced. If it wasn't reinforced then it's just aggregate and as as the water de-grouts the concrete the resistance over the area will increase relative to the rest of the structure.
When high volume fluid, water in this case, scours a disturbance like that for 24 or 36 hours one of two things happens. Either it creates a nice smooth channel or it rips away material looking for a place to create a smooth channel. Concrete isn't that strong when put up against lateral loads and scouring action like that. Great compression strength along the long axis but not so robust at lateral forces (why some buildings have problems during earthquakes).
So what am I basing that on. Extrapolation of what I know happens with hot, high velocity gas over nozzles and other similar structures. I am not aware of a study of venturi erosion of bare concrete by high volume water. That said when the water drops off that edge it has to create a low pressure area under the edge and that's going to cause erosion. The question of course is how fast, which by the way is why most of my posts are clamoring for a current picture. I know it's raining so all the news copters are home but maybe in a few days one will fly over then we can see. Hopefully it's holding at the former edge. I don't immediately see how but hopefully it is.
I watched some live chopper footage from the 13th or 14th of the water coming over the last intact part of the spillway when they were still draining 100,000 cfs. The flow had taken the dirt that used to abut the concrete spillway wall back about four feet and the water was flowing over the break in the former structure. Raged concrete edges. Not smooth or tapered. No defined leading or trailing edges like the blocks in the photo you posted. Although I couldn't see any, one would assume there were also pieces of rebar or steel mesh sticking out of the concrete here and there if it was reinforced. If it wasn't reinforced then it's just aggregate and as as the water de-grouts the concrete the resistance over the area will increase relative to the rest of the structure.
When high volume fluid, water in this case, scours a disturbance like that for 24 or 36 hours one of two things happens. Either it creates a nice smooth channel or it rips away material looking for a place to create a smooth channel. Concrete isn't that strong when put up against lateral loads and scouring action like that. Great compression strength along the long axis but not so robust at lateral forces (why some buildings have problems during earthquakes).
So what am I basing that on. Extrapolation of what I know happens with hot, high velocity gas over nozzles and other similar structures. I am not aware of a study of venturi erosion of bare concrete by high volume water. That said when the water drops off that edge it has to create a low pressure area under the edge and that's going to cause erosion. The question of course is how fast, which by the way is why most of my posts are clamoring for a current picture. I know it's raining so all the news copters are home but maybe in a few days one will fly over then we can see. Hopefully it's holding at the former edge. I don't immediately see how but hopefully it is.
A. Hunter
New Member
Stream now running down the side of the broken main spillway
Source: https://twitter.com/JodiHernandezTV/status/832674181787430913
Internet, cable, and power out here as the storms hit the central California coast. Thanks for the pic, Sean T. Looks like there's still heavy erosion from the muddy outflow flow carving into the hillside, so this ravine could potentially 1.) wear down to bedrock similar to the e-spillway or 2.) it could fan outwards in the coming days/weeks similar to the other side of the waterfall. As mentioned previously, the bottom isn't as important as the top of the spillway, however, it will have impact on debris and the Hyatt Powerplant repair project.
It does look like there is a large chunk of solid bedrock to the right of the bottom of the stream. This might extend further up the waterfall and could explain why the concrete wall on the left side is still intact. Perhaps someone more knowledgeable about geology can advise?
I wasn't able to watch the presser but interesting the media is calling this a "new steam of muddy water." Been watching it develop since Tuesday. I asked an LA Times photographer about it yesterday and he didn't seem to notice it while he was on ground (perhaps distracted by the waterfall or didn't have the right vantage point). I would hope DWR have been aware and watching this develop as much as we have.
Edit: Insert larger image
A. Hunter
New Member
New pics up on DWR website.
Source: http://pixel-ca-dwr.photoshelter.co...fg/G00003YCcmDTx48Y/I00003Q435WBqoi4/BSB-7113
Source: http://pixel-ca-dwr.photoshelter.co...fg/G00003YCcmDTx48Y/I00003Q435WBqoi4/BSB-7113
Photo is taken from a lower angle and more to the North (right) of the spillway than previous photos. However the upper edge of the erosion seems unchanged there.
Paul Bogdanich
New Member
In light of the prior question I think I ought to explain what my interest is here. First I live in Oregon and am a voyeur. On or about February 8th I heard that the deck of the main spillway at the Oroville dam developed a breach. In the unlikely event that anyone earnestly investigates this whole affair, that was and is the original sin as it were. The main problem. How the dam engineers, on a regulated dam, let borrowing animals or water damage remove enough material from under the spillway deck to result in a breach is a major, big time, problem. Because the same people are now the ones giving the press conferences and assurances is the reason that I don't wholly trust what they say. In my opinion they are either trying to gloss over a really big screw up or they are incompetent or both. Take your pick.
Anyway the spillway did in fact fail. The flowing water immediately tore it away, both above and below, until it found an edge it could hold. I hypothesize that the upstream edge that it held was an expansion joint in the spillway. Discontinuous reinforcing material. I further hypothesize that the next time the water causes a side wall to fail that the turbulence from the reinforcing material will likely cause it to tear the structure back to the next expansion joint. I personally think this logic is why they let the water top the emergency spillway in the first place. They had to be scared of something in the main spillway to even think about trying that. Forget the fact that the emergency spillway was even more fragile than the main spillway.
So when, not if (assuming they can't repair it first), the next sidewall failure occurs it could very well tear the structure back to the next expansion joint. If that in fact happens then we, the public, are in a position to ask some intelligent questions to figure out what our odds are. For example, how many more expansion joints are there until you get to the spillway gates? How long, and how much water volume, did it take to make the last section fail? How much water is anticipated to be added to the reservoir between now and say May when it should stop raining? Do those numbers add up? What should people reasonably do and when.
retired mech eng
Member
Just throwing out a thought for consideration, and perhaps self evident and addressed by other posts. With our new "ravine" getting larger and deeper, is it possible that a significant amount of the spill way flow will divert left, and go down this path, and not down the current waterfall? What surprises will that bring? Will it cause the effective leading edge of waterfall to go asymmetric, and direct it towards the north? To me, the exposed surface in the cut near the transmission tower (at the top of the ravine) doesn't look like bedrock, so it is very probable we will eventually lose a big chunk of the spill way up to, and perhaps past the tower.
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whoosh
Member
Agreeing no see erosion uphill, but clearly the water is moving left/south and eroding. I wonder if this is a result of lowering the flows in the spillway. Days ago when the spill was at full tilt, video from the north showing water tearing downhill (to the right) was screaming past the damaged area of missing [north] wall and remaining in the spillway channel, as if it was just moving so fast that it could only go forward unless it actually hit something, which it didn't as it flew past the gap.
I'm just wondering if this new development of water leaving the spillway toward the north (to its right as it flows downhill) is a consequence of only the reduced release rate, or if there is another cause.
Paul Bogdanich
New Member
I can't see where that picture was taken at. Hopefully is is somewhere below the main breach where the water is just carving out a new channel. If it's above the breach the where is the water coming from? It had better not be above the main breach lest we have another newer breach further up. Since I didn't see the transmission towers in the picture I though it was down below somewhere. The picture doesn't make it clear.
This picture?
Is down at the bottom of the spillway, you can see the brown stream flow into the pool. It's nowhere near the "waterfall".
retired mech eng
Member
The picture post #86 is taken at the breach, and I believe the existing breach is where the flow for the new ravine is coming from, although a minuscule portion of the total flow is likely coming from the upstream drainage system (discussed elsewhere).
I think that's largely water splashing over some big rocks, and not really flowing at all. Can't really tell, but it's a tiny amount of water. The stream will do nothing except expose a stream bed, like the emergency spillway overflow did.
What's crucial is unfortunately what is hidden, i.e what is going on under this cloud of water:
However it is a bit downstream from the waterfall, so hopefully additional erosion will proceed downstream. I imagine the waterfall itself must already be landing on pretty solid rocks at this point.
All hidden under tons of water for now. We'll see.
retired mech eng
Member
Thanks for the photo. I think it all depends on how deep the new area gets scoured out at the 8 o'clock position. Perhaps it is already on bedrock. Overall it may not matter much, as the left hand side of the waterfall is not constrained meaningfully much anymore (new flow at the ravine, and bypass flow just left of the left wall), until you get to the north side of the new "ravine".
A. Hunter
New Member
The water in this stream/ravine has been flowing since at least Tuesday when outflow was still at 100k cfs (shown in aerial pics). On Wednesday 2/15, it turned muddy with soil sediment and carved a deep ravine into the hillside as you can see from this DWR picture.
Source: http://pixel-ca-dwr.photoshelter.co...TE/DK-Oro-Spillway-damage-4065-02-15-2017-jpg
Therefore, I don't think the development would be due to a decrease in 25k cfs of water flow since it began before they lowered the flow. That said, you bring up a good point, has the decreased flow allowed for more water to find it's way into the ravine/stream? Today is the first day we have seen media coverage of this and as a result close up imagery.
From Wednesday to today ,I can see that the water stream has shifted from the initial ravine route, it is widening at the base, and finding new places to errode. Will be interesting to see a good clear pic higher up near the cliffs. Although I think those look like they unchanged. Side note: maybe one of the mods can assist with a better comparison side-by-side picture from 2/15 to today?
Scott Gates
Active Member
Topos show the ravine has been there all along ... the only "carving" that mighta been done is the breech finally eroded a better connection it would seem.
Scott Gates
Active Member
Just a reference ... bedrock underlying hillside ...
Is it possible that different spectrum imagery, like radar (or others, thermal?....???) might "see" through the water flow, or at least the spray and splash, and give a clear picture of things visually obscured by water? If so what resolution? Also , I believe there is a technique called interferometry that compares imagery and highlights changes. I may be off on this but, I'd thought the resolution was cm or mm scale on surfaces. If this were the case, it seems it could be a highly useful tool in tracking the rate of headward incision. Beyond this it might be possible to forensically correlate and map waterfall progression with underlaying materials (soil, gravel, concrete, "bad" bedrock, " good" bedrock) This could be applied predictively , in coordination with concurrent mapping of extant surfaces , to perhaps inform discussion or decisionmaking based on likely results to the spillway with different outflow regimes and expected (mapped!!) basal materials were the concrete spillway to degrade farther upslope.
I'd think they would be doing that already. I read somewhere they were using LIDAR, but that might be more for the surrounding terrain - checking to see if that changes.
KenMH
Member
I am very interested if lidar can be tuned to ignore the falling water and capture only the deepest returns, also if the spectrum of return off the rock types versus suspended water is varied enough to tune for that as well. I suspect LIDAR could do something here, but if it has not been 'figured out' yet that could take some time to find the right filters and amount of data needed to get positive results. it could take many more passes with the instrument and a far larger data set than normal to get a solid image.
Scott Gates
Active Member
With the flow reduced already, I would suspect they would simply shut the spillway down over the next few days long enough to inspect it ... I would probably dump a bunch of the rock bags in the side cuts - particularly the left side (looking at the spillway) breach, and see what they do when flow is recommenced ... they are 2500 lbs if I recall and have a pretty good resistance when a bunch are together ... might minimize further outside the wall erosion ... wondered why they didn't try a couple when the breach was small (although they might have and just no pics).
Better dump some of the big concrete barrier blocks in the hole first and then some bags on top ... pump some grout in to it and you've probably made a big difference
Better dump some of the big concrete barrier blocks in the hole first and then some bags on top ... pump some grout in to it and you've probably made a big difference
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KenMH
Member
Good question, there's a whole thread dedicated to it
https://www.metabunk.org/oroville-dam-drains-in-the-spillway-walls-how-do-they-work.t8407/
SeanT
Member
retired mech eng
Member
Yes, agreed very interesting. I'm not sure what to make of the "cliffs" on the right hand side. They don't look very "stable" to me. This could result in a lot of extra debris in the river, perhaps to where the power house is in jeopardy of flooding. And the location of the new potential debris flow, being upstream of the main spillway, is even more problematic than the debris on the downstream side that I was so worried about previously. I wonder how much of what was washed away was expected to be stable bedrock? Perhaps the experts can chime in? Also, as alluded to by Marcus, the flow to the left has diminished significantly. To my untrained eye, this is just reinforcing how difficult this animal is to predict...
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CRM114
Member
Also a great still image at CA DWR:
http://pixel-ca-dwr.photoshelter.co...mDTx48Y/I0000Ml6y1xwkJFY/FL-Oroville-4657-jpg
A large chunk of the lower half of the spillway on the right side of the photo (red circle) is no longer there relative to this photo:
http://pixel-ca-dwr.photoshelter.co...g/KG-oro-spillway-damage-10504-02-09-2017-jpg
There appears to be a lot of new erosion in the past few days in the now "natural" channel on the right carrying the bulk of the flow.
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http://pixel-ca-dwr.photoshelter.co...mDTx48Y/I0000Ml6y1xwkJFY/FL-Oroville-4657-jpg
Interesting for several reasons. For one the cloud of spray at the waterfall seems much higher. It's also nearly all going off to the right. Hard to tell exactly why - but it's going to be less water give a different trajectory and/or changes in the waterfall basin.
A close examination of the right side indicates no change. Note the distinctive pattern under this tree - possibly roots.
There does seem to be some red in the water still. If we boost the color contrast we can see tints of red.
It's impossible to do a comparison without identical lighting conditions (and camera). But it does seem to indicate some soil erosion still going on around the hole.
retired mech eng
Member
Its not super clear, but the Feb. 18 photo seems to show that the drains upstream of the break are not flowing. Or perhaps they are flowing, but are just obscured by the red circle? If not flowing, I'm not super sure what it means anymore (again something for the experts to chime in on), as this forum is moving far too fast for me to keep up...
retired mech eng
Member
Another thought, which I think deserves a separate post, is that a new observer, looking at the photo, would see that the spillway stream has cut off sharply to the right, and has eroded through an area that almost seems to be "uphill". If this had happened further up the spillway (not meant to imply that it could or it will - that is far above my expertise), the erosion would be much closer to the edge of the dam. How much do we know about soil/rock conditions in the area between the spillway and the dam?
deirdre
Senior Member.
An annotated diagram would be useful here. Are you suggesting some significant new erosion to the right? If so, then where exactly?
retired mech eng
Member
I'm having trouble annotating the photo, but will keep on trying (senior moment(s)). In the interim, let me try and paraphrase. It appears to me, and my eyes might just be playing games (different location than previous photos, etc), that the right side ravine that is carrying most of the flow is now deeper on both sides, and the cliffs appear to be higher and steeper. The water is definitely carrying sediment. Perhaps you can perform one of your wonderful side-by-side comparisons with a previous photo?
Compare Feb 11 (left) vs Feb 18
http://pixel-ca-dwr.photoshelter.co...mDTx48Y/I0000_kQrW2SJ8ME/FL-Oroville-1441-jpg
http://pixel-ca-dwr.photoshelter.co...mDTx48Y/I0000Ml6y1xwkJFY/FL-Oroville-4657-jpg
[compare]
[/compare]
Minor addition erosion - to be expected even if nothing was happening in a new scar like this.
http://pixel-ca-dwr.photoshelter.co...mDTx48Y/I0000_kQrW2SJ8ME/FL-Oroville-1441-jpg
http://pixel-ca-dwr.photoshelter.co...mDTx48Y/I0000Ml6y1xwkJFY/FL-Oroville-4657-jpg
[compare]
[/compare]
Minor addition erosion - to be expected even if nothing was happening in a new scar like this.
retired mech eng
Member
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Ln X
New Member
I have highlighted the areas I think retired mech eng is referring to. The small gulley has been noticed about two days ago. However the area circled may have had fresh erosion, but older photos should be able to verify this.
I think the circled area with the tree and large bushes is going to once the big storm passes by. Everything below it is eventually going to be eroded away and stripped down to the bedrock, after that there will be more water flowing rightwards and less flowing leftwards.
As far as I'm concerned this raging torrent could finish off the entirety of the messed-up lower-half of the main spillway as long as there is no erosion causing spillway damage which is closer to the dam.
The only way more of the upper-half of the spillway could go is through the overhang (the concrete spillway hanging over the new cliffs) collapsing, the outflow scouring rock and causing the cliff to recede some more and a new overhang forming, and the process repeats again.
But that will take a lot of time; months possibly years to retreat all the way back to the dam. In fact it could take tens of years since waterfalls make very slow progress eroding away resilient bedrock. All of this is assuming a strong outflow which of course will not last as there will be many dry spells in the future and thus time to repair the main spillway.
If there is solid igneous and/or metamorphic rock then the main spillway has plenty of years left in its current state. But if there sedimentary rock: sandstone, mudstone, siltstone or even limestone, the erosion will work its way quickly backwards towards the dam. Limestone by the way is resilient rock but is vulnerable to water that is acidic or of neutral pH, particularly vulnerable are faults in limestone rock which can allow water to seep into layers deeper underground.
I suspect the engineers constructed the top half of the spillway on a strong rock layer, a rock layer which had a mixture of igneous and/or metamorphic rock.
Are there any geology reports which indicate the rock types the main spillway was built upon?
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retired mech eng
Member
Agreed. But does this mean that when they ramp up the spillway flow again, that the majority of the flow will now take the right hand channel, bringing new conditions to the ravine and to the cliff? It seems today's path of least resistance is different permanently than what is was before. Will that bring surprises?
deirdre
Senior Member.
My thoughts are that would depend on when they ramp it up and whats in the hole. Meaning how much deeper will the hole get. If the hole stays about the same depth as it is now then a heavier release (100,000cfs ex) should jump (bounce out of) the hole the same way it did before.
add: right now, i think, the only reason most of it is going out the hole in the spillway side is because the floor hole isnt filled to the rim with water, due to decreased flow. once the water coming down the spillway fills the floor hole faster than the side broken spillway can release it, the remaining water will skid across the top of the full floor hole.
a sketch would probably help. i'll think about how i can demonstrate my point with household items...
add:
Source: https://youtu.be/M-bMv0C2G5U
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This comparison is from different elevations, so hard to get a precise compare, so I put them side by side. It does look like this region has changed quite a bit in a day. Hard to tell how much with the angle and the lighting.
retired mech eng
Member
Thanks for your response. I think the tail end of the spillway is now trying to put the brakes on the straight downstream path, and encouraging diversion right (more than before). See the attached photo with green annotations (I am getting better at this!). The slab is lifting on the exposed leading edge, and you can see big chunks have already been dislodged.
**I think as well that one reason the gorge on the right looks so much deeper today is that the flow is a bit less than before, and the water level and spray intensity is lower. That being said, there is erosion taking place on the right hand side, and it will be interesting to see tomorrow. Also, the new videos posted in post #1210 of the main thread show some really good shots of the left hand side. If the flow were to be biased towards the left, the stream just outside the 10 o'clock position (see the trees that look like they are on an island) can easily merge with the new left hand ravine, and in fact, I think it has when the flows were higher on this side.**
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Ln X
New Member
But again this is very likely irrelevant to future erosion which causes main spillway damage in a direction towards the dam? Unless the edge of the exposed spillway collapses some more then there must be a boundary to the maximum possible extent of the erosion?
I am visualising a triangular fan-shape zone of erosion downstream of the spillway lip (the highest extent of the structural failure)...
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