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Wow, glad I don't live downstream of this dam!

Discussion in 'The Dungeon' started by kangasj, Feb 10, 2017.

  1. Hooper

    Hooper Well-Known Member

    Yeah, I just saw that somewhere else. I was using a number that I thought that I remembered them saying every morning when I watch the news while getting ready for work. I blame not enough coffee yet. :p

    I should have just said "more than a shit-ton per second" so that I couldn't be called out on it. :D
     
  2. beac83

    beac83 "My safeword is bananna"

    If you are so myopic that you neither know or understand that history, I can't do anything for you.
     
  3. dsapsis

    dsapsis El Jefe de los Monos

    Indeed it's a lot of water. 100k cfs is about 2.3 acre-feet a second.
    The crux to keeping the dam from failing will be continued use of the spillway without it eroding back to the exit gates.
     
  4. Rob P

    Rob P Well-Known Member

    The dam isn't at risk of failure, the spillway is. If you are looking towards the dam the spillway is to the left of the dam and the emergency spillway is to the left of that. Dams are built so they are keyed into bedrock which means that the hill the spillway is on is bedrock which won't just slide away. The danger is that the undercutting of the spillway and the unprotected spillway could slide away in a massive mudslide which itself would be bad by it won't release all the water behind the dam at once so it would be a lesser disaster. This is going to be a problem for a while not only because rod the forecast storms but the massive snow pack we have right now. They're going to have to run that spillway at high flow rates for quite some time which only compounds the problem.
     
  5. sheepofblue

    sheepofblue Well-Known Member

    I also don't believe in big foot or other mythical creatures :beer:
     
  6. IrocRob

    IrocRob Well-Known Member

    No one would be evacuated for a massive mudslide. They have clearly said that there was a real danger of the "emergency" AKA
    "auxiliary" spillway ground eroding to the point of wall failure. As I read it, this would result in an uncontrolled flood of about
    30 feet of water depth from the entire lake (about 15,000 acres) That concern would be big enough to cause an evacuation.

    They are supposedly getting hit with another 10 inches of rain over the next couple days, so I'm still hoping for the best for all concerned.
     
    sheepofblue and kangasj like this.
  7. Newsshooter

    Newsshooter Well-Known Member

    30 feet of water would be a complete dam failure which wasn't likely to happen. I haven't seen any reports from the National Weather Service predicting 10 inches of rain and it's expected to snow above 4-4500 ft which means it will run off slower. 10 inches of rain is more than we got last year in total.
     
  8. dsapsis

    dsapsis El Jefe de los Monos

    That was a long-winded way of saying the same thing I did. If the spillway fails, the e-spillway is moot. If the e-spillway were to fail catastrophically due to a second cresting (because inflow exceeds outflow and the level rises to crest -- like what happened last Saturday,) that 30 feet of water (representing about 450,00 af of water, or about 13% of total lake volume) would likely cause considerable incision resulting in more than just the top 30 feet being released. Regardless of final release, that would cause massive damage and flooding.

    Late today they reduced outflows out of the spillway to 80k cfs, as it appears their models are telling them they enough freeboard to handle the upcoming storms.
    They will not be getting hit with 10 inches of rain over the next couple day. Today's storm largely fizzled, and the front tomorrow is pushing south. The third wave, expected Monday/Tuesday is the one causing concern, with 4 to 8" of water equivalent forcasted for the Feather watershed. However, model accuracy goes way up at 48 hours, so there is a lot of uncertainty now. See here for detailed discussion.
     
  9. socalrider

    socalrider pathetic and rude

    yeah, today through sunday we are getting the second wave you referenced. and im supposed to golf sunday. goddamnit nor-cal, keep your water! :D
     
  10. dsapsis

    dsapsis El Jefe de los Monos

    SoCal is set to get blasted. But like I often am compelled to remind my fellow Golden-Staters (after spending some good time on both Oregon and Washington, as well as on Smith River) -- it's only water; stuff dries. :D
     
    socalrider likes this.
  11. kangasj

    kangasj Banned

    I thought the emergency spillway was at risk which would erode the earth behind the dam which could lead to failure. They're been doing a TON of work on erosion control below the emergency spillway...

    https://ww2.kqed.org/news/2017/02/07/engineers-assess-spillway-problem-at-oroville-dam/
     
  12. kangasj

    kangasj Banned

     
  13. Mongo

    Mongo Administrator

    The level of the water behind the emergency spillway isn't that deep I believe, so it wouldn't be like the real dam itself collapsing.
     
  14. dsapsis

    dsapsis El Jefe de los Monos

    People are having a real hard time understanding this, and part of it has to do with parsing out "dam". The main earthen impoundment (where the power plant is) is not in danger of failing. Both the spillway, and the e-spillway (which is a mini 30' x 1700 concrete impoundment) are. The former could fail if erosion backs up the main spillway chute all the way to the gates causing them to catastrophically fail. I am not sure what the bottom level of the 8 gates are, but its substantial lower than the 870 foot elevation of the bottom of the e-spillway dam. If those gates fail, hell will break loose.

    It appears the e-spillway is secure unless lake level cannot be controlled and cresting occurs again. As stated above, if the e-spillway fails, at a minimum, the top 30 feet of the lake (about 450,000 af) would be released en masse. This is plenty to cause massive damage, and the additional water due to incising is uncertain, but would add to the problem. Like I said, if the spillway can continue to function with releases in the 100k cfs range, it appears the dam system should remain functional to early summer, at which point it can get fixed.

    Currernt work is directed at cleaning out the area immediately under the main dam which is precluding the powerhouse from functioning, where it can add in another 14k cfs of controlled release.
     
  15. Mongo

    Mongo Administrator

    30' at once would suck for sure, isn't that the same amount they've taken a week or so to drain out since the last rains?
     
  16. dsapsis

    dsapsis El Jefe de los Monos

    Between Sunday when they initiated releases and yesterday morning, they were able to get the level down 32 feet. As of midnight last night its at 37 ft down from cresting.
    Controlled releases work; all-at-once not so much.

    Be careful estimating future changes to lake levels though -- while it appears that current outflow capacity is capped at 100k (at least until they get the powerhouse operational, which is currently looking like around 5 days out) the bif unknown in inflow. Modeled runoff into the lake I have seen is estimated at 45-55k, but again, weather can, and does, turn. Hence why the E-vac status remains in place.
     
  17. kangasj

    kangasj Banned

    Ya, looking at the picture in that link I'd guess you're correct.
     
  18. G 97

    G 97 Garth

    They have started to ease back the output from 100,000 to 80,000 in order for workers to get in closer in order to start the repair process for the spillway. The real question is what caused the spillway to break apart in the first place considering at the time outflow was only at 35,000. Max outflow is 150,000. The emergency spillway wouldn't have even come into play if they would have kept the output at a higher level.
     
  19. dsapsis

    dsapsis El Jefe de los Monos

    No. See above.

    Everything I have read is the spillway was designed for 250k cfs, as that was the measured storm flow that caused the blowout of the partially built structure during the epic 1964 Christmas flood (something on the order of a 100-200 flood event, depending on the curve fit of the GEV model).
     
  20. 600 dbl are

    600 dbl are Shake Zoola the mic rula

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