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  1. Scott Gates

    Scott Gates Active Member


    Correct - different cut - at parking lot end of weir ... I am pretty certain that is the area that prompted the evac order ... the hardening next to the main spillway is largely intact and the "cut" there was almost entirely just the roadway washing away.

    Here is one of your earlier pics marked to show the flow - how lateral flow was created and then concentrated with the downhill flow to increase the cutting force.

    Keep in mid this pic reflects something less than 8,000 cfs flow over the emergency weir ... the force is not large - but it is steady. I suspect as long as the bags stay intact the force even at 12,000 cfs or somewhat higher probably would not be able to dislodge the weight of those bags of rock.



    [​IMG]
     
  2. SFX

    SFX Member

  3. Mick West

    Mick West Administrator Staff Member

  4. Carl Leoanrd

    Carl Leoanrd New Member

    KCRA has live video of the helicopter rock bag drops. I'm not seeing the rock drops going in any of the holes that have been talked about here today.

    They are dropping into some small gullies at the extreme left side of the broad weir.
     
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  5. Mick West

    Mick West Administrator Staff Member

  6. Carl Leoanrd

    Carl Leoanrd New Member

    I'm also seeing a cement pumper at the end of the road just past the main spillway. A lot of rock trucks on the road over the dam, and some excavators working slightly downhill between the main spillway and the dam.
     
  7. Geonerd

    Geonerd New Member

    Great find!

    Sounds like a typical metamorphic melange found in much of California, and looks about right to describe the bluish-grey rocks visible at the base of the main spillway. Many of the rocks that come out of the metamorphic process are fairly hard (marble, schist, serpentine, hornfels, gneiss, etc.). The spillway rocks in question are clearly pretty robust, or they would have eroded away years ago. Assuming the hill/mountain is made of the same stuff, and isn't too deep beneath the surface, flow through a breach in the emergency dam would take years to carve away the rock.

    [​IMG]
     
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  8. Geonerd

    Geonerd New Member

    Looks like erosion has reached bedrock in a few places. This begs the question - why not move a "little bit more" earth (in comparison to the main dam!) and extend the weir structure all the way to solid rock? I suppose the weir was always considered to be a sacrificial structure, and was never expected to survive the 700,00cfs monster flood the e-spillway was designed to accommodate.
     
  9. Scott Gates

    Scott Gates Active Member


    It would be great if someone could find information on just how the weir is built ... I cannot believe it is not firmly anchored to bedrock ... that said it is largely backfilled on the lake side - with soil nearly to the top at parking lot end ...
     
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  10. EricL

    EricL Member

    This is correct, but note that the dark, wavy line on the embankment face opposite the camera's point of view is the original ground surface. As was pointed out by some sharp-eyed posters earlier, the roadway fill makes it look deeper than it otherwise would, but it's still a very deep hole.
     
    Last edited: Feb 13, 2017
  11. Mick West

    Mick West Administrator Staff Member

    20170213-164459-go0jl.

    20170213-164624-7u3k5.
     
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  12. Mick West

    Mick West Administrator Staff Member

    There's an "Army Corps of Engineers Oroville Dam Reservoir Regulation Manual" mentioned here:
    https://elibrary.ferc.gov/idmws/common/downloadOpen.asp?downloadfile=20051017-5033(13724888).pdf&folder=19973004&fileid=10849040&trial=1
    But I have been unable to find a copy.

    The intent was to have it in case of a worst case flood, a "probable maximum flood"
     
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  13. Scott Gates

    Scott Gates Active Member

    Sure doesn't seem to be any urgency on the part of DWR?

    They could have been flying rock up to the parking lot all night and all day - even if they didn't know where to use it yet.

    Could have mobilized equipment up there all night and day so they had everything in place.

    Could have been working all day on an access road into the cut ... down along the left side of the curve of the failed road and hauled enough rock to fill cuts enough to get equipment to the base of the emergency spillway.

    They have heavy lift choppers on site in operation to move more rock faster ...

    They could have had CalDOT dragging square highway barriers up there (not tapered "jersey" type) and stockpiling to use for stabilization.

    Looking at the rock bagged so far in the parking lot - it ain't much.

    I fully understand a lotta planning and hoops to deal with - but mobilization of resources and equip is independent of all that ...
     
  14. MortarBoarder

    MortarBoarder Member

    Go look on the first page, at picture of the bedrock cut for the normal discharge intake, or look on the current Google Maps aerial photo. The normal overflow structure is obviously installed on bedrock, but we don't know how much of the spillway rests on bedrock. But then, the emergency spillway treats the hillside as expendable, so perhaps that's how the lower part of the spillway was designed... in case of failure. Maybe only the top of the spillway is absolutely required, but we'd rather not find that out experimentally.
     
  15. Mick West

    Mick West Administrator Staff Member

    Attached Files:

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  16. SFX

    SFX Member

    I just checked the spillway in the old document Mick found.

    spillway.

    The latest images don't look the same at all.
     
    Last edited: Feb 13, 2017
  17. Mick West

    Mick West Administrator Staff Member

    The ESRD perhaps seems little complex, it also does not seem to tie in with the text . The vertical axis is simply the water level in the lake. The line that starts on the left is the emergency CFS output for a given lake level. if it's at 848.5, then the release it 150K CFS.

    20170213-173049-akg8o.

    That's saying the Main Spillway is rated for 296K cfs. It does not give a figure for the emergency spillway.

    The ESRD is actually the diagram for emergency releases from the main spillway, not the emergency spillway.
     
  18. OgeeWeir

    OgeeWeir New Member

    The Emergency spillway does not inspire confidence:
    Ogee Weir.
     
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  19. Mick West

    Mick West Administrator Staff Member

    Depends on what is underneath, and how they are connected.
     
  20. Mick West

    Mick West Administrator Staff Member

    20170213-173813-hwnkc.
     
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  21. Mick West

    Mick West Administrator Staff Member

    Which latest images? It looks like pre-incident images, and obviously looks different now.
    20170213-174832-xgobj.
     
  22. Scott Gates

    Scott Gates Active Member

    Chart 18 .... Plan & specs of spillway and overflow outlet ...

    A small "tab" at bottom combined with its weight, seem to the the "anchor" ... although it is back filled to within maybe 4 feet of the top on lake side.

    Chart shows at 902.58 (+1.58 over spillway) flow would be just over 10,000 cfs ...



    [​IMG]
     
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  23. Mick West

    Mick West Administrator Staff Member

    Interesting difference in quotes here:
    http://yubariver.org/wp-content/upl...g_Oroville-auxiliary-spillway-major-risks.pdf



    But in this FERC filing, note the text that is missing from the above.
    https://elibrary.ferc.gov/idmws/common/downloadOpen.asp?downloadfile=20051017-5033(13724888).pdf&folder=19973004&fileid=10849040&trial=1


    And I can't find the text "An unarmored spillway is not in conformance with current FERC engineering regulations." anywhere.

    The California Water Research doc quoting from somewhere else?
     
  24. deirdre

    deirdre Moderator Staff Member

  25. EricL

    EricL Member

    Well, that drawing looks to be the plan that they followed. No connections to the bearing surface are shown, and it would be very odd to include them. I do wonder about that tiny ridge that extends down from the back edge, and to me, that raises the possibility that maybe they first dug a deeper excavation to the depth of firmer material and backfilled it to footing grade with concrete, and provided that base with a "keyway" to accept that ridge.

    If no such base and keyway were provided, the normal procedure would be to rely on the extreme mass and stable shape to "keep it where they put it", and the substrate would likely be evaluated simply in regard to whether adequate bearing capacity is present to tolerate the "toe pressure" resulting from tipping forces (not so much from water, but due to the pressure of saturated backfill). That's a standard which would not require that very "durable" material be present. It would also be normal to simply protect the ground surface just in front the edge from erosion, and the protection originally provided (just as what's shown on the drawing) is pretty minimal. While as it stands, the structure looks vulnerable if in any situation where the underlying material can erode as easily as it already has at some locations quite close by, if they do a very good job of adding erosion protection for some distance downstream of the structure, that should pretty well eliminate future risk of undermining. As others have pointed out already, it looks like the little bit of that kind of improvement which was already done before yesterday's over-topping, held up pretty well. I think there likely would have been severe erosion right at the base, had they not done that.
     
    Last edited: Feb 13, 2017
  26. SFX

    SFX Member

    The one he used, and I quoted. Obviously there has been some serious erosion of the original rock. And this is a spillway that is rarely used.
     
  27. deirdre

    deirdre Moderator Staff Member

     
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  28. skicopper

    skicopper New Member

    Very interesting read. It seems that because of the damage to the main spillway, they within the guidelines to use the emergency spillway.
    An emergency spillway may be advisable to accommodate flows resulting from misoperation or malfunction of other spillways and outlet works . . .

    It also appears that the 'emergency' spillway isn't even considered an emergency spillway until the pool reaches 911'. A full ten feet above the lip.
    The lower ten feet of the ungated spillway at Oroville Dam is best characterized as an auxiliary spillway. As described in the Engineering Guidelines, “Auxiliary spillways are usually designed for infrequent use, and it is acceptable to sustain limited damage during passage of the IDF. HOWEVER, no one really knew for sure what kind of damage one foot of water going over that lip could cause. I can only imagine what 10' would look like!
     
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  29. Mick West

    Mick West Administrator Staff Member

    Looks the same to me. Perhaps you are reading too much into a photocopied photo.
     
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  30. Jeff Semenak

    Jeff Semenak New Member

    The spillway design flood pool is a full 16ft. above the emergency spillway at 917 ft. to achieve it's rated output of 296000 cfs. Hard to believe the Emergency Spillway only flows 54000cfs. at 16 feet of head height over the Weir; 4ft. before over-topping the Dam.
     
  31. MortarBoarder

    MortarBoarder Member

    Nice.
    So the emergency overflow is rated at 440,000 cfs with a maximum of 16 feet of water flowing over it.

    One detail missing below the bottom of the bottom diagram is cross section D-D. It shows a cross section of the emergency overflow. The overflow structure extends below the level of the reservoir bottom, and has a lip extending down to resist the outward water pressure. There is only a short concrete lip at the bottom of the outflow surface and no deep construction below the exposed face.

    [​IMG]
     
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  32. MortarBoarder

    MortarBoarder Member

    I think he's referring to the smooth face of the bare rock below the dragon's teeth, compared to the more recent image.
     
  33. Dylan J Duverge

    Dylan J Duverge New Member

    Fantastic thread, signed up just to comment. Based on all I have read there in here, there are two questions which remain unanswered for me. Firstly, do FERC regulations require or not require an emergency spillway to be armored to the nearest stable area or watercourse, and 2) is the spillway base founded 100% on top of bedrock? Mick, the difference in quotes you cite is interesting, and I wonder if there may not be a conflict in the two. Perhaps there is a different understanding of to what degree, or length, the emergency spillway must be armored. I don't know if FERC or other regulations get to that level of detail since the question is so site-specific. The most troubling thing is how slight the emergency spill was (compared to design estimates) versus the degree of problems that were generated. The location of bag drops is troubling, and suggest the vulnerability may lie in an inadequate length of the engineered structure. From much of the evidence provided in this thread, it seems as though there may be significant protection in the underlying geology, but I would love to see someone dig up any boring logs in or near this site to elucidate the degree of strength afforded by the bedrock. Yes the formation is "bedrock", but it is notorious for being discontinuous, craggy and riddled with fractures and weak zones. The agencies were clearly opposed to the cost implications of the comment by Friends of the River, and if the lake level tops the spillway again they may be eating their words. Significant hillside erosion and downstream effects, in my view, are acceptable consequences of an emergency, but certainly not failure of the emergency spillway.
     
  34. deirdre

    deirdre Moderator Staff Member

    the lip is the top, right? how do you get 10 feet of water (or 911') if the water starts pouring out at 901'.

    I'm so confused o_O
     
  35. Geonerd

    Geonerd New Member

    Well, SURE, there's some erosion. The vertical gouge at the left of my GE picture is nearly 100 ft long!
    BUT, I think you are underestimating the tremendous violence that the rock is subjected to when the main spillway is flowing. Any material this side of high-strength concrete is going to suffer some damage in the face of the vibration and pressure spikes subjected to it by the the falling water. That the rock has, over the decades, withstood hundreds of hours of this abuse is testament to its strength and cohesion. If this were soft sandstone, shale, or some other soft material, you might have some cause for concern. This stuff? IMO, even at several hundred K CFS over the e-spillway, it would take weeks to produce significant downward erosion.
     
  36. Jody Bourgeois

    Jody Bourgeois New Member

    There hasn't been this much hydraulic excitement here since the heyday of hydraulic mining. "Hydraulic mining in the Sierra Nevada" covers the environmental impacts of that mining as well as other human activities such as logging and grazing, on the draininges including the Feather and Yuba, all the way to the Sacramento delta and San Francisco Bay navigation. This extensive report was commissioned by Congress to the USGS when petitioned by the miners, who had been enjoined from mining, partly because of damage to farmlands and other lands downstream of the mining. Marysville was particularly hard hit by floods which strew gravel all over their lands. https://pubs.usgs.gov/pp/0105/report.pdf
     
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  37. Geonerd

    Geonerd New Member

    At the moment, given what I think I understand about the structure, I 'think' the e-spillway was never designed to provide flood control, or to survive being overtopped without damage. In a sense, it was never really meant to be used, except in an .... EMERGENCY. ;) IMO, it's sole purpose is to save the main dam from being overtopped (and quickly washed away!) by any conceivable flood produced by storms, rapid snowmelt, etc.
     
  38. Dylan J Duverge

    Dylan J Duverge New Member

    I would point out though that the examples of exposed bedrock, such as that along active streams or cliffs have become exposed over geologic time for the very reason that they are the strongest. When you uncover bedrock beneath hillsides, it has undergone various degrees of hillside weathering, chemical and physical, and may not represent the hard bedrock that many people think of...
     
  39. MortarBoarder

    MortarBoarder Member

    I think on the previous page was a picture of the emergency spillway, and at the top you can see the adjoining wall next to the normal control valves. The people on top of that wall are maybe 6 feet tall, and look at the drop down from where they are standing to the top of the emergency spillway.

    Up to 16 feet of water can be flowing over the top of the emergency spillway. It will be a nice smooth surface, until it reaches the ground below.
     
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  40. MortarBoarder

    MortarBoarder Member

    True, but the bedrock here has been described as "hard amphibolite". So someone has decided that it tends to be relatively hard.
     
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