Oroville Dam Main Spillway Waterfall Erosion Watch

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Mick West

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This is a split-off thread from https://www.metabunk.org/oroville-dam-spillway-failure.t8381/

Since the eroson of the main spillway is the key risk now water levels are under control, I've created this thread to keep track of any changes in the erosion at the "waterfall" location. Inevitably there will be some "head cutting" and the erosion will the move up the hill. However it seems to have stopped since Feb 10, and the hope is that it is now stable with the spillway spilling over a rock-bedded location.

This is a single topic thread on the progression of the waterfall erosion. Please stay on topic as much as possible. Off topic posts may be edited or removed.



Closeup on the latest DWR photo taken 8:55 this morning.

20170215-085456-q1f9s.jpg


Appears pretty consistent with this image from Feb 11, so that's good.
20170214-132216-m7jwj.jpg
 
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How much time before the damage reaches the gates?
If the main spillway fails farther back

Of course if the main spillway fails further back then there will be major problems. The thing is there's absolutely nothing to suggest it is eroding back at all in the last three days. It seems entirely unchanged.

I posted the comparison before:
Closeup on the latest DWR photo taken 8:55 this morning.

View attachment 24613

Appears pretty consistent with this image from Feb 11, so that's good.
20170214-132216-m7jwj.jpg

There's no detectable difference. And yes, I labeled on image as 2016, but quite obviously it's 2017. You can look up the image yourself.
http://pixel-ca-dwr.photoshelter.co...00PCdyEjzDuNk/FL-Oroville-2601-02-14-2017-jpg

I also posted an earlier comparison showing how it went back 330 feet in a few days. The obvious inference here is that it was receding rapidly backwards and then it stopped.

Please refrain for baseless fear mongering here. Even in the unlikely event of the entire main spillway rapidly collapsed there's plenty of time to shut down it down, and then evacuate people over at least two days before the emergency spillway flows. And that's the worst case. Right now the main spillway is running perfectly fine at 100K cfs. Probably because it's running on rock.
 
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And comparing the video to this one shot 33 hours earlier, looking at the North edge of the Waterfall
20170215-075358-le00d.jpg
There has been no visible erosion there over that time, which is good.

Of course there's no guarantee the waterfall will continue to work, but at least there are no signs of it failing.
 

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If the current main spillway situation remains stable for weeks/months of high flow, is it possible they could just finish off the end of the existing concrete flume [...]?
 
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If the current main spillway situation remains stable for weeks/months of high flow, is it possible they could just finish off the end of the existing concrete flume [...]?

Certainly the cheapest option. I think there is some possibility they will do that on a temporary basis at least.
 
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Reminder
This is a single topic thread. The erosion progression at the waterfall. Please do not drift off topic. Discussions so be restricted to if the erosion is progressing, how it might be stopped, and what the immediate effects will be of progression.
 
Avoid using that orange fence as a primary landmark. It is a safety barrier for workers and will be moved based on safety decisions. The power line towers are presently convenient markers, but might get removed soon.
 
Avoid using that orange fence as a primary landmark. It is a safety barrier for workers and will be moved based on safety decisions. The power line towers are presently convenient markers, but might get removed soon.

The fence is useful, so long as you check it's position relative to other things. The bushes are not going to move.

Unfortunately it's had to find shots from precisely the same angle.
20170215-100941-vqnar.jpg
 
great confirmation, crack is not a crack.

Is a tweet or twitter post, with-out a source even allowed here? (probably better to debunk and move on anyway.)
 
Is a tweet or twitter post, with-out a source even allowed here?
Photos are photos. The "crack" was just a small bit of erosion side-lit by low sun so it looked darker and hence deeper.

This misidentification could easily have been magnified into fears that the side of the waterfall bowl was going to collapse - so it's good to debunk it as early as possible.
 
Can you quote what they actually said?
around 14 minute mark (nothing abnormal, just the design criteria of the dam)

6:50 " The spillway has been stable for a number of days now. It's stable at this 100,000 cfs that we are releasing now. We want to keep that right up. as we continue to move more water out of the reservoir to be able to absorb some of the wet weather that we're experiencing, apparently right at this moment, and then into the future days and weeks"

"we've taken 20 feet out of the reservoir which poses far less threat to the infrastructure. but as ive indicated before, alot of water is up within the watershed and were monitoring that on a continuous basis to see when that run off comes.

[construction progress talk]
11:21 we'll continue to manage the reservoir releases. as we look at the storms coming in, we're feeling very good about the resevoir conditions. And in fact, as long as the weather kinda plays somewhere along as forcasted, we're looking actually at reducing the amount of water that's being discharged through the flood control spillway or some are calling the main spillway.

So dont be surprised if we start backing off of that release.., that's an important part as ive learned in the last couple days, an important part in how we manage how the water is coming from the reservoir and flowing through the flood control structure and out, down the concrete chute that was damaged. And so, we're looking at that plan ramp down, based on the design criteria for the damn.

So the idea there is of course we dont want to tear our flood control structure up anymore then it already has. So don't be surprised if you see the department reducing those releases. Again we're looking forward based on our forecasts and some point later in the month we may see a little increase in reservoir operations but again we have an amazing amount of [stories] that we continue to approve on, on a regular basis.


13:00 Maybe to back up a little bit for those watching reservoir elevations, i've talked [alittle about] our primary target is 850 feet. right now we'e at 878 feet at abut 10 oclock this morning. We're dropping somewhere around 8 inches an hour.
...
As i said, we dont anticipate a rise in elevation in the coming days but we continue to monitor the weather and forecast that forward into the future.


14:02 Reporter question: Why would you consider reducing the out flow right now

Answer "well we wouldnt need.. the way the main spillway is designed, theres actually a chute thats carved into solid rock that goes into the reservoir that we cant actually see. [explains intake area is under the reservoir water] it's channeled. and if we continue to remove water from t he resevoir at this 100,000 cfs that can affect the condition of the rocks up front of the flood control structure and we dont want to compromise that also. Theres a design model based on the elevation of the water, they put limits on how much you can release at a certain time. so, again, we'll be stepping that down based on the water surface elevation to make sure that we operate within the design criteria for that flood control structure.

[answers another question]
19:25 any concern we have related to the main spillway is related to its stability. So were pushing alot of water for a number of days over the end of that structure and it's holding up very well. But we are monitoring that spillway as well as all the other littl epieces that we have in place to make sure that if anything starts to change, we're aware of that right away....Right now im really happy witht he function of the structures we have in place.
Content from External Source
 
There will be cavitation and venturi erosion on the trailing edge of the concrete, I do not care how it is attached to the bed, eventually "I Feel" there will be damage and erosion working upward.
Of course there will. The question is how long will it take.
 
Of course there will. The question is how long will it take.

Two questions, how good are the supplies of pictures (I was looking for them when I found this site) for continuing reference and two, does anyone know anything about the geology? From the press conference is sounds like they put the gates of the main spillway on or near some bedrock. I hope it extends out on the spillway side a good bit.
 
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It looks like there might be a parallel erosion channel sharply cutting into the hillside directly left of the waterfall.

The partial erosion channel is the result of the useage of the emergency spillway, which is no longer in use.

Can anyone address the increase in sediment to the left of the main spillway?

It's from various construction round the corner near the power station
 
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The partial erosion channel is the result fo the useage of the emergency spillway, which is no longer in use.



It's from various construction round the corner near the power station
New poster here too and i think he is talking about this.
erosion.jpg
 
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20170215-205858-6ctha.jpg
The partial erosion channel is the result fo the useage of the emergency spillway, which is no longer in use.



It's from various construction round the corner near the power station

The channel I'm referring to is much narrower and to the right of the bedrock e-spillway channel. In the picture below, it's in between the red line and the runoff of water north of the concrete sidewall of the waterfall. It has gone from waterfall runoff on Tuesday to heavy sediment today. Pic source DWR. http://pixel-ca-dwr.photoshelter.co...K-Oro-Spillway-damage-02-15-2017-IMG-4211-jpg

16716005_1324841790904092_3162118306214832886_o.jpg
 
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The partial erosion channel is the result fo the useage of the emergency spillway, which is no longer in use.



It's from various construction round the corner near the power station

First time poster here as well. Great forum. I think that A. Hunter's statement "parallel erosion channel sharply cutting into the hillside directly left of the waterfall" is referring to the flow (new) that can be seen to the left side of the left wall on the main spill way. It is shown clearly in the attached photo (very high definition and very useful). Also note the small stream of water just further to the left of the wall. Will the stream get larger and further accelerate the erosion to the lower surface bounding the main spillway?
rx1HIA2.jpg
 
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I wasn't able to attach the photo in its original high resolution, but if you go the original posting for photo rx1HIA2 above (I can't seem to find it now - was it removed?), you should be able to zoom in the area of interest...
 
I retract my previous statements. While there is some red sediment coming from the construction round the corner this is clearly a new ravine being formed from this spot:

20170215-220419-cdjat.jpg

20170215-220331-caxfj.jpg
20170215-220305-tyfrx.jpg

If this continues it will probably just lead to a widening of the fan below the waterfall, and the continues destruction of the structure of the lower parts of the spillway (already pretty much a total loss)
 
rx1HIA2.jpg
I have cropped the original photo down to the area of concern. If you look closely you can see a large bypass flow just to the left of the left wall, and a small "creek" with running water a bit further to the left. Reading his latest posts, I think A. Hunter is referring to the creek.

A couple of additional concerns come to mind with the newly formed/forming ravine. More sediment and debris will make its way to the river, and will complicate plans to restart the power station. Also, it might accelerate erosion upstream, as the water can focus equally on the left side and the right side of the undamaged spill way, above the sink hole. Also, I am not an expert, but the larger the eroded area on the hillside, the more prone the area will be to large scale mudslides.
 
I retract my previous statements. While there is some red sediment coming from the construction round the corner this is clearly a new ravine being formed from this spot:

Thanks everyone for your input and I appreciate the close up images. I was having trouble locating them. This forum has been an incredible wealth of information. It will be interesting to see what happens with this newly formed ravine and how the waterfall continues to shape with a continuous 100k CFS output (for how long?) and impending storm/rainfall.
 
With this new flow which is causing erosion on the right side (right side downstream from the dam) of the main spillway, the steep cliffs close to the electricity pylons could collapse a bit and threaten the two electricity pylons nearby. Perhaps the electricity pylons should be removed to stop them getting entangled upon the main spillway?
 
With this new flow which is causing erosion on the right side (right side downstream from the dam) of the main spillway, the steep cliffs close to the electricity pylons could collapse a bit and threaten the two electricity pylons nearby. Perhaps the electricity pylons should be removed to stop them getting entangled upon the main spillway?
That was already covered in the other thread ( https://www.metabunk.org/oroville-dam-spillway-failure.t8381 around page 16 or so) but there are plans to fly the towers out by chopper once there is time/availability/cooperative weather.

Aaron Z
 
No new pictures on the CA Dept of Water Resources website today (02-16-17). Anyway of seeing how the back-cutting or lack thereof on the main spillway is proceeding? Outflows are still 100,000 cfs. Inflows are up to 37,000 cfs with the rain. Lake level still falling.
 
Some inferences of moderate validity about erosion prognosis might be drawn from examination of the vegetation in the high resolution photo provided above in post #32 by retired mech eng (https://www.metabunk.org/attachments/rx1hia2-jpg.24694/). I hope that link is correct. I draw also from comments on geology by other astute and knowledgeable posters here, to wit, that the solid grayish rock is more competent than the brownish orangish rock and (certainly) soil. That fits my field experience and is backed up by plenty of science on the weathering continuum from competent bedrock, through "weathered rock" to "soil" which after all is just highly weathered rock with a higher level of biological content and activity than harder rock. It is never ideal to speculate without the benefit of a site visit, but I perceive areas of broken woodland canopy with shrubby, probably chaparral understory on grayish substrate, and areas where there is much more (bright green) grassy cover on browner/oranger substrate. Based on my field observation in analogous foothills sites, the former vegetation generally grows on more competent rock with a very thin layer of weathered rock/soil. (This is somewhat corroborated by the shallow depth of gullying of the gray rock, seen in photos in posts #30 and #31, above.) The latter grows on more weathered material with deeper soils; which is more susceptible to erosion.

The failure of the spillway occurs just about right where a band of the grassy/orangish soil abuts the spillway. There is the grayer, hypothetically more competent material downslope on the left side, and extending far upslope on the right side (viewed as in the photo; thus right bank and left bank of the spillway looking in the direction of flow). Where the browner, hypothetically weaker material intervenes, that's exactly where the failure is. There is clearly some very competent rock still sitting at the bottom of the waterfall, right in line with the chaparral/grayer material on the left side (in the photo). And, remarkably, a lot of the concrete (at least, the visible left wall) is still intact despite being subjected to a lot of energy impinging on exposed upper edges. I suggest that this means that the concrete that's placed right on the gray material, not on (heavens!) fill or the more weathered material, is not likely to erode much even under severe circumstances of extended periods of 100,000 cfs flow.

There is a narrow band of orange brown soil with darker green vegetation along the left side of the spillway; I speculate that that represents a body of backfill placed after excavating down to build the spillway. That's where the minor new erosion noted by Mick West is occurring, caused by water escaped at the sidewall breach above. It's either backfill or a tongue of that more weathered material; in either case, more susceptible to erosion than the gray stuff that's still happily bathing in the bottom of the waterfall.

Returning to the critical upper part of the spillway, above the breach, the woodland/chaparral on grayer material seems to run along the whole of the right side. There is slightly higher headcutting on the left side than the right, again supporting the statement that the woodland/chaparral/gray substrate is more resistant. It is not reassuring that the headcut scarp on that right side is brown/orange material, but the exposed rock peeping out through the vegetation above is gray, and hopefully that means getting more competent as one moves uphill. In any case, I think the pattern of vegetation and other clues suggests that the hard gray rock certainly extends (at the surface, overlain immediately by the concrete) partially underneath the intact upper spillway. Probably the construction documentation does not even show precisely its extent there, but the fact that the headcutting did not propagate much uphill from the original failure of the concrete suggests that it probably extends right across. Given how well pieces of the concrete in the lowest gray-rock area have remained attached, it's plausible to infer that the upper spillway is also well attached, in close contact, to competent rock and will probably not fail and headcut all the way up, even if fractures develop or additional pieces of the slab are lost.
 
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