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  1. EricL

    EricL Member

    I think Dylan's point is still valid, since it's clear that a large amount of shallow bedrock has eroded at this site. This matches up with what he was saying, as long as the deeper, less-weathered rock turns out to be the harder material that you mention (and that's probably exactly what would be found).
     
  2. Jonathan Neubauer

    Jonathan Neubauer New Member

    That Ogee is not going anywhere, concrete doesn't float. In fact, water is 62.4 #/cf, and concrete is 150 #/cf, so there are simply no buoyancy effects that would negate the forces of water flow over the top; in fact the opposite, overburden and dynamic effects of the water above the weir would probably improve the reliability, although it has been a long time since I designed one of these. Given the flow characteristics of large bodies of water, there is no backside turbulent flow, impact of debris is a nominal force and water is simply very predictable because it has no shear strength above freezing.

    It's a straightline slope from peak, which matches the pressure curve on the lakeside.

    The lakeside is keyed into bedrock- this section may be to to scale, but it is easily misinterpreted by the layman- we do not have the specs, which were probably determined by the rock type and design code at the time. That weir is 3 stories tall and weighs at least 70,000 pounds per foot of linear length. In other words, that's over 4 concrete trucks full of concrete per foot (don't forget the key!).

    So the real threat is scour and fracture of the bedrock that it is keyed into. With 70 kips per foot gravity weight and a 30 foot deep lateral section, the bending strength of the weir should be more than adequate to resist fracture, even if there is a breach of the bedrock.

    The fact that they are working overtime to put boulders, cobbles and concrete on the backside to protect it while they are releasing 100,000 cfps tells me that they know exactly what they are doing, and they know a lot more about the situation than they did 4 or 5 days ago.

    The overburden has been removed by the usage of the emergency weir, so they can see the supporting bedrock and actually build on it (thank you scour! Work smart- let the water do the work for you!), the emergency weir has been tested and proven (again- there are no impact loads or anything other than normal dam building stuff- as long as the foundation isn't compromised, the weir will do just fine), and the scour rates on the spillway are acceptable enough to run it almost full tilt to buy them some time.

    Let the engineers do their job, they have handled it exceptionally well so far.
     
    Last edited: Feb 13, 2017
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  3. skicopper

    skicopper New Member

    Someone correct me if I'm wrong but the way I read it is that there would literally be ten feet of water pouring over the emergency spillway
     
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  4. stuart little

    stuart little New Member

    i think more attention needs to be paid to the upward destruction of the main spillway . head cutting? I see no reason to believe that any portion of that spillway is in fact "on bedrock"... therefore i see no reason that the cutting doesn't go all the way up.. you'd only need a shallow layer of fill under one side for the thing to self destruct. in 10 days ... where do you think the waterfalls head is? i say way to close to the gates... and they need to make it to summer? good luck
     
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  5. Jonathan Neubauer

    Jonathan Neubauer New Member

    They are running it full tilt right now for a reason, I would speculate the higher velocities are putting more forces on the "target" rocks and debris a football field away, rather than turbulent flow that would undercut the surviving spillway.

    Running it at 100,000 cfs versus 25,000 cfs might be safer for the upstream spillway.

    If I were going to guess they are draining it to give them as much time as possible to let the repairs at the emergency weir be put in place and cure. Once the damage to the spillway gets to a certain point, they are going to cut it off and let it fill back up and go over the weir if they have to.
     
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  6. Scott Gates

    Scott Gates Active Member

    So ... I took the section of the ogee weir given from my post #384 and have done some rough interpolations ...

    It appears the dimensions for the profile view of the emergency 'ogee type' weir is... appx 48 feet at its base and 60 feet tall overall - with an appx 6 foot thick x 12' apron on front and a similar sized "foot" underneath at rear .... and the entire weir is appx 900 feet long (not including the parking lot section) ...

    The more research I did it seems clear that the entire weir is the same profile for its full 900' length ... (more next post)

    If that is correct - then the total volume of the 900 feet would be (guesstimate) 58,000 cubic yards ...

    1 cu yd concrete weighs appx 4,056 lbs ... meaning the entire 900' long weir structure weighs appx 235.25 million pounds ... or about 117,600 tons.

    A pretty massive object ... with the appx 6' x 12' x 900' key at bottom read, and the appx 6' x 12' x 900' toe ... the base is appx 60' ... this roughly matches measurements in Google Earth etc ...




    [​IMG]
     
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  7. skicopper

    skicopper New Member

    I agree. That main spillway might have to remain open for the next month or more. This is still a severe problem.
     
  8. Carl Leoanrd

    Carl Leoanrd New Member

    That is correct. It's a hard to comprehend situation for sure. Its only possible if that same amount of water is coming into the lake from the forks of the Feather river.

    In this last rain event there was considerable flooding upstream in Portola and the photos I saw of one of the upper forks looked positively scary.

    Crazy amounts of water outflow come from even crazier inflows.
     
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  9. Scott Gates

    Scott Gates Active Member

    We can see from this aerial how the 12' splash "toe" vs the exposed width of the weir in an overhead aerial photo narrows the further 'uphill' it goes on the down slope side ... the closer it gets to the parking lot.

    The red line would be the appx width of the base from reservoir side to front edge of the "toe" if it was 60' ...

    As the soil rises higher along the downstream side the width of the spillway exposed in an overhead view would get smaller.

    It is highly unlikely it seems - that they would create all different sizes of forms to pour the spillway itself = especially if poured in place ... but even if poured offsite in sections it would seem ...

    [​IMG]
     
  10. Mick West

    Mick West Administrator Staff Member

    Full tilt would be over 200K cfs. Normal max is 150. Emergency use of main spillway is higher. Right now it's just 100K
     
  11. alec

    alec Member

    We have witnessed the destruction of the concrete spillway. I believe the term that describes that is nickpoint migration. Concrete is a very hard incredibly durable material. It is "strong" in compression . In tension a brittle material can snap...think glass. The concrete spillway was "designed" to flow what? 250,000cfs . It has been described as a waterfall now, some mentioned 300 - 400 feet high. I think the correct drop is less, but waterfall sounds accurate. It's likely not direct erosion of the very durable concrete surface that's driving this. However, as a system, the concrete spillway is being destroyed. My guess, and only a guess is that the massive turbulent flows are undermining the support below and the unsupported concrete then breaks off under the pounding. It's likely more complex than that with many other contributing factors . The system as a whole has failed.
    Likewise, erosional undermining of greenschist facies metavolcanics can not be reduced to a determinist claim based on the hardness of the strong rock. The rock system is non-uniform and more complex than just the rock hardness. Please take a close look at the bedrock adjacent to the concrete spillway in photo #2 of posting #17 by Mick (thank you for the stunningly clear photos Mick) . If you look closely you will see a series of parallel vertical fractures oriented roughly northward (which is consistent with regional patterns). The location is on the east bank of the spillway near the top.
    This oriented series of fractures can absolutely have an effect on erosional qualities. (As an extreme unrelated end member example, I would ask you to consider The Devil's Postpile's columnar jointing of basalt, a very hard, strong, competent rock and understand that those joints absolutely do affect how that massive chunk crumbles) (As a second example, consider highly fractured competent rocks in a fault zone, seismically active range like the San Gabriel Mountains....they can crumble in your hands) Even the orientation of those fractures can affect erosion rates.
    A pertinent local example is the "hole" we've been discussing. Turbulent water dug that rather quickly and deeply. Thankfully, as no water is issuing from it , the "boil" is not under the hydraulic influence of the lake. This last statement is a big deal, a fundamental concern with these large masses of water that ended happily in this specific case. The hole was dug directly into the hard rock under discussion. Clearly the theoretical competency of a given rock type is not the only factor that needs to be taken into account in understanding how this system behaves.
    Local explicit evidence has been on powerful display these past weeks. This evidence is developing before our eyes and should help us to get idealized concepts to empiric understanding of the forces at work here.
    Regarding weir depth, without doubt it starts at a point some safe distance below the dam crest. It is impossible to manage even the smallest reservoir filled to the peak from wind effects alone. I thought someone in a long press conference a few days back described it as large enough to pass inflow with a full reservoir, and then some. Given that we've seen 150,000 - 190,000 cfs within the last month and given the erosion what we've seen from the 12,000cfs over the weir, and given what we've seen from the 100,000cfs down the concrete spillway today, it doesn't seem that high flows over the weir would be a good thing regardless of what the original design intent was.
     
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  12. Jonathan Neubauer

    Jonathan Neubauer New Member

    Full tilt over a damaged spillway should be zero, so I think 100,000 CFS is full tilt in the eyes of the guy with his hand on the lever.
     
  13. Mick West

    Mick West Administrator Staff Member

    Sure, but before that 55K was "full tilt". Right now it depends on how desperate they are. If the coming weather system swells up then "full tilt" might be expanded.

    Luckily 100K seems to have largely worked out with minimal additional erosion. I think they will keep it up for weeks.
     
  14. alec

    alec Member

    a bit more on rock description, please correct and supplement if askew.
    Metamorphic = change of form from Greek, in geology i think altered by heat and or pressure ,typically by burial. Deeper equals hotter and higher pressure. Greenschist facies describes a heat and pressure range. Schist, from schistocity, or tendency to split. An earlier post mentioned these local rocks are often identified as volcanics because the metamorpism is not severe. Don't know if these are all correct for this example, but might be helpful.
    The other thing that's been mentioned in various forms is piping and a boil. Often the surface expression of this is a sediment laden water flow. It's important to keep keen eyes out for this. It's also important to understand that high sediment flows can occur many other ways and that has not been identified here so far . Still any sediment moving anywhere here is removing material that used to be part of the hillside, and as has been previously posted can create voids which gravity may fill.
     
  15. Scott Gates

    Scott Gates Active Member

    The exposed vertical amount of the 60' overall height on downstream face ... at the main spillway end appears to be appx 45 - 50 feet guesstimate ... and on the reservoir side at the same end it appears to have appx 30-40 feet are exposed above the soil level.

    At the parking lot end the downstream side face appears to be as little as 20-25' are likely exposed, and on the reservoir side as little as 8 feet or so ...

    IF the entire weir is the same profile - 60 feet tall at back side and 60 feet wide (incl the "toe" at front) at the base ...

    ... it would seem that the base at parking lot end would be at least 35 feet deep on the downstream face and more than 50 feet deep on the reservoir side.

    ... it is also close to 500 feet from the parking lot end on the reservoir side before you reach a depth equal to the appx depth of the base of the weir.

    The erosion at the parking lot end on the downstream side - it would seem - would have had to be at least 35 deep to get below the base of the weir ... and then would have to travel nearly 500' to reach water at that level.

    On the main spillway end - with 45-50 foot exposed on the downstream side and guesstimate 30-40 feet on reservoir side it would be easier for a headcut to get below the weir ...



    [​IMG]

    [​IMG]
     
  16. Jonathan Neubauer

    Jonathan Neubauer New Member

    Full tilt would be the 750,000 cfs number, which is so far out of reach it is irrelevant- so I was just commenting on a practical full outflow volume.
     
    Last edited by a moderator: Feb 13, 2017
  17. Dave Little

    Dave Little New Member

    First, thanks so much to Mick and the people that run this. It's so refreshing to have a hysteria free zone and intelligent participants. Also sad that it's so rare these days, but that's another issue.
    While I know the preservation of the dam structure is the primary thing right now, I'm wondering where all the water is going. Is it getting to the central valley where it can be used? And maybe even stored? Like in aquifers? Or is it headed out to sea?
     
  18. Mick West

    Mick West Administrator Staff Member

    Actually the outflow from Oroville is less than normal. Given the amount of rain we had (and the level of the lake) we would expect 150K cfs, but we are at 100K cfs. They can't let out as much as they want because of the damaged spillway. So to answer "where is the water going", it's still in Lake Oroville.

    The outflow from Oroville serves ag land around Yuba County, but ultimately makes its way to the Sacramento/California Delta, where some is for ag, some is for for Los Angeles, and some flows to the sea.
     
  19. RedNeckGeek

    RedNeckGeek New Member

    Watching the local news here in Oroville, there was coverage of the Shasta dam discharging at 70,000 CFS, the maximum allowable without an emergency order. That's going into the Sacramento River, same as where the Oroville Dam discharges will end up. It was also stated that Shasta is only 6' below the dam top, so they're in the same, but not quite as acute, situation as Oroville. And we're headed into what could amount to a solid week of additional rainfall, something like 6" just through Sunday anyway. So there are at least two concerns:

    Can the dams discharge enough water to create space for the upcoming rain? A simple back-of-the-envelope calculation for Oroville tells me that they'll only get another ~15' of drop between now and Wednesday night when the rain starts falling, not the 50' they're estimating. That comes from 0.3' of drop/hour x 48 hours. Shasta is even bigger, and discharging at a lower rate, so isn't their problem even bigger?

    Do other dams along or contributing to the Sacramento River system face situations similar to those at Oroville and Shasta? Do the rivers and associated levees south of those discharges have sufficient capacity to handle the new inflows that the dams can't contain? The Feather River system seems to be limited to 150 CFS, but what happens south of the Feather/Sacramento confluence? What's the capacity of the Sacramento River and associated levee system in downtown Sacramento?

    I'm sure somebody in DWR is looking at scenarios like this, but we aren't hearing anything about it in the media. I for sure don't want to join the Chicken Little crowd, but are we being protected from these kind of thoughts to avoid a large scale panic? Please show me the faults in my thinking...
     
  20. Mick West

    Mick West Administrator Staff Member

    Shasta has huge "emergency" spillways. See those gates at the top?
    20170213-221140-9r338.
    The five tiny outflows there are around 50K. The spill gates go to 186K cfs.
    https://www.usbr.gov/mp/slwri/docs/Appendices/MP700_SLWRI_046_AppxPhys_H&H.pdf

    Total release of 287K. Peak inflow this season was 171K, so no problem - unless the drum gates all fail.
    20170213-222017-utfl2.
     
  21. Dave Little

    Dave Little New Member


    At some point the drop should be more than 0.3'/hour, right? Since the lake's sides are sloped. I still doubt that they'll get to 50', but maybe closer than 15'. Not sure how significant this might be, but it should help. I'm curious about the math too, and what the odds are of them completely losing control sometime in the next couple months.
     
  22. Mick West

    Mick West Administrator Staff Member

    Small. I doubt they will have the use the emergency spillway again if the main spillway holds up, which it looks like it is doing. Right now I'd put money on them just continuing about 100K cfs for the next 1-2 months.

    However the next ten days will be telling with a storm coming. Has the main spillway stabilized? That's probably the biggest question. Then if it hasn't then is the emergency spillway up to the job?

    I get the feeling that the excitement is over. Now it's just a bunch of engineering, and finger pointing. We'll see.
     
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  23. Mick West

    Mick West Administrator Staff Member

    There's your problem:
    20170213-224603-ro5gw.
    Wider:
    20170213-224719-sp4sd.
     
  24. Mick West

    Mick West Administrator Staff Member

    Detail of the gully by the road in the SW. Remaining rock has quite a few fractures, but is probably good short term. Of course this rock probably isn't the problem. It the rock that got eroded away that's the problem.
    20170213-224925-e976c.
     
  25. Carl Leoanrd

    Carl Leoanrd New Member

    I sure hope that you are right. It is pretty much all up to Mother Nature as to what happens. Looking at the long range models she is not done with the rain. Not crazy rain like last week, but it looks like rain on at least half the days for next week or two.
     
  26. Scott Gates

    Scott Gates Active Member

    Yep ... I'm not smart enough to figure it out ... but the 12,000 cfs - spread across 900' - at appx 1.6' head over 901 ... just doesn't seem that much force ... I think it was the sustained flow that was the culprit ... which has now scoured most of the fractured near surface material.

    These lateral sideslopes are an issue IMO ... most weirs seem to be uniform height on down slope side - don't get these lateral flows then that can concentrate is certain areas.

    I think I'would set a couple of those jersey barriers perpendicular to the weir at top of each of those "steps" that create a sideslope to keep water headed straight downslope ... maybe even a set every 30 feet or so?

    Like straight toward weir from where those guys standing by that pipe
     
  27. Scott Gates

    Scott Gates Active Member


    Hey - ya you guys - go over and lay down on that apron so I can check my measurements ... yep - looks like about two of you .... 12' looks just about right!
     
  28. David Larson

    David Larson New Member

    I can't say with absolute certainty, but I believe this screen cap was of the work that was done prior to the flow over the emergency spillway and its resulting erosion. We're seeing a lot of video being posted now that is not in chronological order.
     
  29. Carl Leoanrd

    Carl Leoanrd New Member

    I believe that there was a map with flow capacities up thread. Basically, if Shasta goes over 70k it causes local flooding in the known flood prone areas.

    Right now a lot of the Central valley rivers are high, but below or just at low flood stage. If it rains a lot flooding becomes more likely. Simple as that.
     
  30. Mick West

    Mick West Administrator Staff Member

    What might this pipe be?
    20170213-230508-395dr.
     
  31. Mick West

    Mick West Administrator Staff Member

    This is 10th Feb:
    20170213-230814-4b1se.

    And 13th (today)
    20170213-230932-eqr1a.

    20170213-231008-nbik8.
     
  32. Scott Gates

    Scott Gates Active Member

    Looks like an old light pole ;-)

    Square base - curved top ...

    Are those pics from the CA AWR site?
     
  33. Legion V

    Legion V New Member

    Maximum flow of the main spillway is 296,000 cfs @ 917' water level, lower maximum flows at lower water levels.
     
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  34. Mick West

    Mick West Administrator Staff Member

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  35. Scott Gates

    Scott Gates Active Member

  36. deirdre

    deirdre Moderator Staff Member

    well if they arent planning on having to use the emergency spillway again (fingers crossed) its probably better if they take the time to do it right the first time vs just slapping a quick fix in there. Its going to cost enough without doing something, then having to pay to remove it, if they decide on a different long term plan.

    Of course that depends on the math with the upcomign rain this week and if they think the emergency spillway will stay dry.

    plus he said they were actively working on removing debris from the river. at 20 mins in press conference. i havent seen any video of work today at all so i dont know if they were actually working on the river. ?
     
  37. The area around the dam site is the Smartville Ophiolite, a suite of rocks that make up oceanic crust (1).
    ophiolite.


    The dam itself is underlain by sheeted dikes, a gabbro, which when fresh, is incredibly competent(2). However, gabbro is composed of a mineral assemblage that contains many minerals that decompose when located near the surface such as olivine, pyroxene, and plagioclase, among others. Migrating water downward through the bedrock causes chemical weathering of these minerals and greatly reduces the strength of the rock. gabbro3b.
    weathering rind on gabbro.
    peridotite soil weathering.
    a depiction of how this type of mafic bedrock weathers deep below the surface. Note peridotite is ultra mafic and does not underlie the spillway, just using this as an example to show the deep weathering of bedrock occurs.



    Sheeted dikes are inherently inconsistent in composition, leading to areas susceptible to greater weathering. The extreme act of emplacing these rocks from deep below the ocean floor onto the continent (obduction) leads to further faulting, folding, and low temperature metamorphism, creating more zones of weakness in the rock.



    Fresh rock will be some form of gray, dark gray, light gray, gray green, etc. When weathered, the color of the bedrock becomes orange, progressing towards red hues when highly weathered.



    Both spillways are built into this bedrock that has varying degrees of weathering. The original failure of the main spillway can be attributed to this weakened, weathered bedrock just by noting the color. The gray-green bedrock downstream of the original failure still has concrete adhering to it and is withstanding the torrent. The orange stuff is not faring so well, while the red highly weathered bedrock (soil in a geological sense) quickly eroded away.

    The image of the main spillway during construction shows an orange area exactly where headcutting approached closest to the ogee weir. e spillway parking contruction anotated.

    We will find out whether or not the weathered bedrock weathers the change in the weather next week.

    (1)http://www.water.ca.gov/orovillerelicensing/docs/DEIR_070521/06 Ch 04 Env Setting Part 1.pdf
    (2) at 8:15

    Source: https://www.youtube.com/watch?v=g1sR9vuBYp4
     
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  38. Scott Gates

    Scott Gates Active Member

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  39. OE1FEU

    OE1FEU New Member

    Correct me if I am wrong here, but if by a dry spillway you mean just rainfall and not another overflow over the lip, then continuing this work should be OK. Assuming that they will fill the area with rocks and boulders and pour concrete over it in order to mitigate erosion effects, then this should be fine for the weeks to come.

    Concrete does not need to be kept dry in order to harden. In fact, dried out concrete is more brittle than poured concrete, which hardens through a process called hydration.
     
  40. Joe Ebeni

    Joe Ebeni New Member

    I'm not an engineer or a hydrologist so I didn't appreciate what 100k CFS meant and what the dam engineers are dealing with. So I looked at Mississippi flow https://waterdata.usgs.gov/mo/nwis/current/?type=flow At Saint Louis the median flow of the Mississippi is 121,000 cfs. Holy cr&p that's a LOT of H2O, unless I have missed something. I kept checking to see if I had an order of magnitude error but I don't think so. Did I miss something?
     
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