Tags:
Thread Status:
Not open for further replies.
  1. J McNabb

    J McNabb New Member

    The above diagram applies to closed conduit, pressurized flow only. The hydraulic gradient is the pressure in the pipe. Open channel flow at the Oroville Dam spillway behaves according the hydraulics of a 'free surface' - much more complex flow, and is not pressurized. The hydraulic gradient is the free surface from one point to the next. When open channel flow speeds up because of slope change to a steeper slope like at the Oroville Dam spillway, the flow depth becomes less and the hydraulic gradient is still the water surface. The water velocity increase has a force of its own, but it is not pressurized. For an interesting study, search for hydraulic papers on the Karnafuli Dam spillway failure in East Pakistan. Huge slabs of concrete were sucked off the dam because of pressure fluctuations in the spillway vents caused by the appearance of the hydraulic jump in an unexpected portion of the spillway
     
  2. JCL

    JCL New Member



    Was posted 2 hours ago, what is this new flow?
     
  3. KenMH

    KenMH Member

    To add, I believe if that dam cannot provide irrigation to the central valley of California water costs and less production will increase the cost of produce for hundreds of millions if not billions around the entire planet, not a huge amount but given the production of the area it would have an effect. I wonder how much?
     
  4. Pozzolith

    Pozzolith Member

    [​IMG]
     
    Last edited by a moderator: Feb 17, 2017
    • Informative Informative x 1
  5. CRM114

    CRM114 Member

    A portion of flow appears to have jumped to the other side of the main spillway for some reason. There is the muddy stream and new (to me anyway) flow along the outside of the wall.

    upload_2017-2-17_14-35-26.
     
  6. stuart little

    stuart little New Member

    in the bottom left of your post 908 you see the muddy flow? thats it but its down by the dental teeth...!!!! not very interesting other than those dredges will have a lot more work soon.... this is a big event something could easily "overrun" them . this new flow could further the complete daming of the feather and send the flows back at the dam.... ?
     
    • Like Like x 1
  7. Don Turner

    Don Turner New Member

    My point about the age of the spillway is an important one. If the drain pipes under spillway floor are rotted out, then it would be a reasonable assumption that concrete slab anchors would also have experienced similar corrosion. It has been my experience in working with older anchor installations that replacement is necessary because, as I stated in an earlier post, older installations used older methods derived from open-pit mining and were regarded as temporary, where as with a permanent structure like a dam, then permanent installation methods are called for. l agree that cavitation is a likely process that occurred. Cracking, spalling, delamination and joint offset are prime contributers and it looks like from the photos that maintenance of the concrete surface was done to the extent that it could be. But, it is difficult to look under the concrete, though it is possible with specialized tools, to see how big the voids are and the condition of anchors that hold the concrete panels in place. The USBR paper we are using as a reference here even states that once cavitation initiates, aeration is not effective to prevent structural damage. At that point, the only way to prevent damage is to limit spillway discharge volume and velocity, which was not possible here. In other words, something was going to break no matter what.
     
    • Like Like x 1
    • Informative Informative x 1
  8. Pozzolith

    Pozzolith Member

  9. Thanks for posting this. My concern today would be if the debris that is coming from the new "ravine" (see other thread regarding extent of spill way erosion) causes an additional 8 feet of pooling prior to, or despite, the planned dredging operations.
     
  10. Don Turner

    Don Turner New Member

    t
    Appreciate the references. Thanks
     
  11. CRM114

    CRM114 Member

    Good points all, except in this photo, the anchors in the hanging spillway wall footer are clearly visible and appear to be intact, whereas the material they were anchored to is gone.

    upload_2017-2-17_14-51-8.

    The now missing "rock" here appears to be deficient as opposed to the anchors.
     
    • Useful Useful x 1
  12. Scott Gates

    Scott Gates Active Member

    I'm sure a bigger picture will show additional sloughing of the embankment below the electric tower which allowed the breach outside the main spillway wall to connect thru to the hillside and allow water to connect to that natural ravine. That ravine is all blue-green bedrock and I suspect will see minimal if any erosion (other than topsoil)

    I also suspect this could be a direct result of the reduction in flow to 70,000 cfs ... slow the water down and it has more chance to fill into the break in the sidewall and into the void below the electric tower ...

    This is silty debris and it enters the river below the still huge flow from the main spillway, which should rapidly disperse it downstream.

    IMO ... of course ...
     
  13. Pat Dilling

    Pat Dilling New Member

    http://www.water.ca.gov/swp/contractor_intro.cfm

    From my time at DWR I recall that there are 14 Water Contractors who support and use the State Water Project. The largest one is the Metropolitan Water District in Los Angeles. I had a chance to ask my State Representative James Gallagher if the Water Contractors would be on the hook for the cost of the repairs and he replied that they definitely will be paying for a portion of it, but could not say how much at this time. Of course they would likely pass on those costs to their users.
     
  14. Don Turner

    Don Turner New Member

    True. This is, what we called in the Geotechnical business, the best test pit you could have. Lots of forensics to keep people busy.
     
  15. stuart little

    stuart little New Member

    the whole lookers left "gulch" is in danger now(imo)... and if that goes, its possible to dam the river sending the flow back at the dam. not trying to scaremonger but... more sediment on the downstream pile makes a reversal of flow more likely IMO. this is a big event on a massive scale... it could easily overun mans efforts to contain it.
     
    • Like Like x 1
  16. The term soil is a matter of semantics. A layman would consider soil to be topsoil, aka the O horizon and A horizon. A geologist considers soil to be everything overlying unweathered bedrock. Above the green line in the figure is the topsoil, below it to some depth I would call saprolite. This saprolite recently (in geologic terms) developed in the metavolcanics.
    The metavolcanics are likely composed of basalt that the sheeted dikes, composed of diabase, circled in blue intruded through during the formation of oceanic crust at a mid oceanic ridge during the Mesozoic. Hydrothermal fluids circulate through the crust, likely following pathways of least resistance. The rock in these pathways can undergo hydrothermal alteration as outlined in figure 2. The red circle around the yellowish substance, is likely weathered, hydrothermally altered basalt.
    The underlying cause of the failure of the main spillway could be this yellowish, hydrothermally altered material as postulated by Dr Rocdoc. http://www.rocdoctravel.com/2017/02/oroville-dam.html.
    main spillway feb 17 anotated.
    hydrothermal circulation.
    figure 1 from post #882
    figure 2 from http://blogs.agu.org/geospace/2015/11/25/tracking-down-hydrothermal-vents/
     
    • Informative Informative x 2
    • Like Like x 1
    • Useful Useful x 1
  17. Geonerd

    Geonerd New Member

    Probably easier to just call the Air Force to drop some 'bunker buster' bombs on the high spots. They'll burrow 20~30 feet into the rock before exploding, carving out a path of crushed, easily eroded, rock.
     
  18. MortarBoarder

    MortarBoarder Member

    Drain pipes would have been exposed to water.

    The anchors had some grout protection. Page 100:
    https://archive.org/stream/zh9californiastatew2003calirich
     
  19. J McNabb

    J McNabb New Member

    I believe you are misreading the information. 350,000 cfs is the maximum release from both spillways when the water level is at the maximum emergency level it can be prior to dam overtopping.
     
  20. Don Turner

    Don Turner New Member

    I think something more surgical and elegant can be done, such as controlled blasts, to shape a new topographic surface. Survival of nearby structures and lower lines is important (this is dam for Petes sake). Not saying that I agree that anything needs to be done here, but it's best not use a club when a hammer will do.
     
    • Like Like x 1
  21. CRM114

    CRM114 Member

    I believe I see grout adhering to the anchors in my picture post above. Seems like the grout was good.

    Excellent link. The confirmation of altered rock brings up the possibility of chemical processes, low pH being the most familiar to me in altered rock. The consequence could be corrosion of metal or weakening of concrete, even pulling clogging of (drain) pipes with chemical deposits.
     
  22. Mick West

    Mick West Administrator Staff Member

    • Like Like x 2
    • Informative Informative x 1
  23. Don Turner

    Don Turner New Member

    True, that's what it says. But, grout surrounding a 1 inch diameter rebar of unknown depth does not by itself prevent corrosion of the bar. As I have said before, at the time, construction practice relied on open pit mine techniques. The holes drilled for the bar insertion tended to be the minimum diameter needed to fix the bar in the hole. Nowadays, we would require a minimum of 1 inch of grout cover around the entire length of the bar. We would also require sacrificial bars to be installed and pullout verification tests performed to verify the adequacy of our design. And now that there has been a failure, I would bet all the change in my pocket that all those procedures will be done when it comes time rebuild the spillway.
     
  24. sushi

    sushi Member

    A question for the geologists.

    If as Rock Whisperer suggests there was a degraded segment of rock, what is the possibility of that strata extending diagonally across the area of the Flood Control Spillway back to the area of the parking lot at the far end of the emergency spillway?

    [​IMG]

    The above is the best image I could find. It shows the area of the damage to the FCS as a black shape on the spillway. You can also make out the corner of the upper boat launch parking lot at the point that the access road turns into it. There is a natural gully connecting these two points. This gully was further eroded when the emergency spillway over-topped.

    Since water takes the path of least resistance, is it possible that the weathered rock associated with the FCS damage extends across the site and is the reason for the eroded channel originating at the parking lot corner? This channel, or gully, descends across the site, appears to create the weakness in the area of the FCS, and then continues down to the lower arm of the Feather River. This is the same pathway the water from the damaged FCS followed.

    Is this evidence of a zone of poor rock extending diagonally down across the site?
     
  25. Scott Gates

    Scott Gates Active Member

    Not true. The stable blue-green bedrock was completely apparent in the channel water is now flowing thru - from the top of the hillside to the river. Some topsoil will wash into the river from increased flow in this natural spillway, but there is no apparent likelihood of hillside collapse.

    And as I noted, the topsoil is 'fines' material ... dirt ... which enters the river next to and downstream from the large flow from the main spillway. That flow will disperse these fines downstream.

    And IF it were a problem the solution is simple. Turn flow thru the spillway off - stop the erosion ... and clean the debris
     
  26. Scott Gates

    Scott Gates Active Member

    I think something more surgical and controlled would be preferred ... to do just the necessary amount to open to bedrock ...
     
  27. MortarBoarder

    MortarBoarder Member

    Nope. Find 917 feet near top left of chart, as that's the maximum "Design Flood Pool". The curves on the right are at 350,000 for the emergency spillway and 296,000 for the main spillway individually. At that point there's about 16 feet of water flowing over the emergency spillway.

    [​IMG]
     
    • Like Like x 1
  28. Mick West

    Mick West Administrator Staff Member

    Note the above image has a 2x vertical exaggeration in the terrain rendering, which I did to make the ridges more apparent. It's actually more like this:
    20170217-151026-qc8a1.

    You can also do 3x, which makes things overly dramatic.
    20170217-151127-i9afz.
     
    • Like Like x 1
  29. Shadowwalker

    Shadowwalker New Member

    • Like Like x 1
  30. Mick West

    Mick West Administrator Staff Member

    • Like Like x 4
  31. Brad P

    Brad P New Member

    You may be right. It isn't real clear. However, the Main Spillway is listed as 296k cfs and has a total opening of 4,620 sq. ft., whereas the Emergency Spillway has a crest length of 1,730 ft. The water flowing over the crest would only need to be 2'-8" deep to equal the same cross-sectional area. It looks like the Emergency Spillway is meant to handle 16 ft of water over the crest. (Crest elev. minus Freeboard, above spillway design flood pool minus Emergency Spillway Crest Elevation or 922.00 -5.00-901.00 = 16) So the total cross-sectional area above the Emergency Spillway would be 27,680 sq. ft. If the water is moving at a little over 12 ft./second, that would give you 350,000 cfs.

    Of course I could be reading it wrong, or I might have screwed up the math. Plus the Main Spillway will have a greater head on it.
     
  32. Don Turner

    Don Turner New Member

    Yes. This. Standard practice is to obtain several representative samples of soil and rock to test pH and design corrosion protection, either galvanization or epoxy coating of bars and concrete reinforcement for the predicted design life.
     
  33. Twominds

    Twominds New Member

    Hi, new here. Lowland archaeologist without real knowledge of reservoirs. Reading and learning a lot here.

    When I saw post #883, I wondered if the big concrete dents would still be there. In some pictures, the lowest part of the spillway seems not completely destroyed. I see a smooth flow, indicating a bit of concrete bed, in the upper right part of the picture in post #911, and what looks like the leftmost dent. If they're still there, would they still help lessening the impact of the water on the outflow pond and its other bank? Not contibuting to more erosion there, that might add to the build-up that's a problem for the power plant?
    Or is the general water flow so chaotic that any surviving dent doesn't make a difference there anymore?

    I can't put the image of post #911 here (obsolete mac with only partially functional browsers). Sorry about that.


    Edit to add: https://www.metabunk.org/oroville-dam-main-spillway-waterfall-erosion-watch.t8402/page-3, post #85, new picture shows that at least three dents are still there, and it looks like they do spray the part of the wather that flows at the left side well enough that it doesn't slam into the far bank of the pond. Nor, looks like, the water from the right side. So at least that doesn't add to the problems for the power plant.

    Thanks mod, for adding the picture from #911!

    mod add: photo from 911
    upload_2017-2-17_14-35-26.
     
    Last edited: Feb 17, 2017
  34. MortarBoarder

    MortarBoarder Member

    You mention "dam overtopping". The graph I just posted shows that at dam-top height, the emergency spillway alone would carry 440,000 cfs. That number is not an accident, as it is the 450-year flood inflow number. Most of the dam descriptions, however, assume that the dam is being operated and never has to deal with that.

    From the spillway design description, from page 100 of https://archive.org/stream/zh9californiastatew2003calirich

     
  35. deirdre

    deirdre Moderator Staff Member


    Moderator Note - deirdre
    If you left click a post number it will give you the link to that comment, that you can then copy/paste into your post or hyperlink it to the number you type.
     
  36. Mick West

    Mick West Administrator Staff Member

    It helps me if I look at it backwards and sideways:
    20170217-154258-lc1pd.

    Then it's just a graph of how the flow rating increases as the lake height increases. The "Combined" curve is just adding the other two together. It goes all the way to 750,000 cfs. The limit for the main spillway is 300,000 cfs (when it gets to the lip of the main dam)
     
  37. Scott Gates

    Scott Gates Active Member

    • Informative Informative x 2
    • Like Like x 1
  38. Scott Gates

    Scott Gates Active Member


    Water flows downhill. Water flowing downhill cannot get to the dam from the spillway damage location.

    And pictures of the underlying ground conditions in the damage area show the left side of the spillway is blue-green bedrock.
     
    Last edited: Feb 17, 2017
  39. Jody Bourgeois

    Jody Bourgeois New Member

    It's a challenge to keep up with this site! Perhaps this topic lies among all the pages. What role might cavitation have played in the original spillway failure? I know that cavitation was implicated in the near-failure of the Lake Powell Dam system in the 1983 floods.
     
  40. Jody Bourgeois

    Jody Bourgeois New Member

    I am with you here. I am fascinated by dams and their engineering (bridges too), and maybe it's possible to fulfill this criterion If you think you may need it, you have to test it for some (certainly not all) of those cases. I am thinking about earthquake engineering and also tsunami engineering such as sometimes worked and sometimes failed in 2011 northern Honshu. Or what happened in Christchurch. That is, how do you test for an earthquake or a tsunami? Granted you can do lab tests and also design in factors of safety, but seems like engineering for disasters requires design beyond what can in actuality be "tested"
     
Thread Status:
Not open for further replies.