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So far, the only failure foreseen is to the auxiliary spillway which would definitely lead to an uncontrolled release of water from the lake, but is a separate

So far, the only failure foreseen is to the auxiliary spillway which would definitely lead to an uncontrolled release of water from the lake, but is a separate structure from the main dam. There's definitely worries about the erosion on the main spillway moving back upstream towards the dam, but that is something folks are going to have to look at and consider over the remaining duration of the water season, unlikely to be a danger tonight.

lisper 10y ago
No, the emergency spillway is part of the dam. Failure of the spillway could lead to failure of the entire dam. It's not likely, but it's possible. Once large quantities of water start going where they weren't designed to go, all bets are off.
- djcapelis 10y ago
  It certainly could, but they are literally separate structures, as repeated stated by the actual engineers who maintain the dam.
  - jcranmer 10y ago
    The hillside underneath the overflow spillway is literally washing away. You can see downhill portions of the spillway where the waters ate away 10, 20 feet of vertical elevation. If that erosion backs all the way up to the reservoir itself, then the lining could fail (much as the main spillway did). At that point, it doesn't matter if the dam is still standing, if there is a gash right next to it lowering the effective maximum water level by several feet. I don't know enough about the geology of the area to know how likely it is to happen. But history does show that dams can go very quickly once erosion reaches the dam/reservoir, so alarm isn't exactly unwarranted.
    - kobeya 10y ago
      It'll hit bedrock.
      - kobeya 10y ago
        Why is this being down voted? The geology of the area is such that the emergency spill off can't be eroded down to the valley floor. That's why the location was selected.
      - deleted 10y ago
        [deleted]
- Tloewald 10y ago
  You should look at the dam from maps or satellite. The spillway is off to the side, away from the dam (clearly, by design), and the emergency spillway is on the far side of the main spillway from the dam, so while the spillway failing would be terrible it should not damage the dam itself.
  - lisper 10y ago
    Looks like you're right. I read somewhere that the spillway was part of the dam structure, but now I can't find that reference any more, so I guess I must have misread it. However, my original comment was still substantially correct. See http://www.sacbee.com/news/local/article132356269.html http://www.sacbee.com/news/local/article132356269.html "It’s not going to be the (main) embankment failure, but it’s a failure. If it does happen, there’s nothing saying that the ground is going to stay where it is. That force of water will start tearing that hill apart, and it could eat back into the reservoir and drain the reservoir.

lisper 10y ago

No, the emergency spillway is part of the dam. Failure of the spillway could lead to failure of the entire dam. It's not likely, but it's possible. Once large quantities of water start going where they weren't designed to go, all bets are off.

djcapelis 10y ago
It certainly could, but they are literally separate structures, as repeated stated by the actual engineers who maintain the dam.
- jcranmer 10y ago
  The hillside underneath the overflow spillway is literally washing away. You can see downhill portions of the spillway where the waters ate away 10, 20 feet of vertical elevation. If that erosion backs all the way up to the reservoir itself, then the lining could fail (much as the main spillway did). At that point, it doesn't matter if the dam is still standing, if there is a gash right next to it lowering the effective maximum water level by several feet. I don't know enough about the geology of the area to know how likely it is to happen. But history does show that dams can go very quickly once erosion reaches the dam/reservoir, so alarm isn't exactly unwarranted.
  - kobeya 10y ago
    It'll hit bedrock.
    - kobeya 10y ago
      Why is this being down voted? The geology of the area is such that the emergency spill off can't be eroded down to the valley floor. That's why the location was selected.
    - deleted 10y ago
      [deleted]
Tloewald 10y ago
You should look at the dam from maps or satellite. The spillway is off to the side, away from the dam (clearly, by design), and the emergency spillway is on the far side of the main spillway from the dam, so while the spillway failing would be terrible it should not damage the dam itself.
- lisper 10y ago
  Looks like you're right. I read somewhere that the spillway was part of the dam structure, but now I can't find that reference any more, so I guess I must have misread it. However, my original comment was still substantially correct. See http://www.sacbee.com/news/local/article132356269.html http://www.sacbee.com/news/local/article132356269.html "It’s not going to be the (main) embankment failure, but it’s a failure. If it does happen, there’s nothing saying that the ground is going to stay where it is. That force of water will start tearing that hill apart, and it could eat back into the reservoir and drain the reservoir.