5 ms·

A failure of the emergency spillway could compromise the west side of the entire structure, no? What prevents that outcome?

by ubu7737 10y ago

mikeash 10y ago
The base of the emergency spillway is bedrock, so it can only erode down that far. That's 30ft below the top of that spillway, which is why everyone talks about potentially having a 30ft wall of water hit downstream communities.
- ubu7737 10y ago
  I just watched Dept of Reclamation video on the designed failure of the Auburn Cofferdam. I get it now.
- AnimalMuppet 10y ago
  I'm not a geologist, but... Didn't the main spillway failure erode some of what was considered "bedrock"? Isn't the bedrock somewhat more erodable than the term "bedrock" would lead you to expect?
  - mikeash 10y ago
    I'm not either, and I don't know! Total speculation: water partway down the spillway is considerably more violent than water just spilling over the top, so while bedrock may not resist the former, it can resist the latter. Another wild guess: the main spillway hasn't eroded any bedrock, just concrete, dirt, loose rocks, etc. If anyone actually knows versus my wild guesses, I'd be most interested.
  - LukaAl 10y ago
    Don't know the details of the projects but from the pictures posted (here and elsewhere) it seems that only topsoil was eroded. Yes, bedrock is not indestructible, it could get eroded from water, but it takes times. Plus it get eroded slowly over time. The main concerns was the use amount of water released by the failure of the spillway. For sure the water keep flowing over the collapse spillway would erode the bedrock lowering it, but at a slower pace...
  - tod222 10y ago
    Some…yeah, where some is the 1.7 million cubic yards of rubble now clogging up the Thermalito Diversion Pool. [1] When you look at photos or drone videos of the erosion near the main spillway, it's clear that an immense amount of rock has been eroded away (the color changes from brown to gray). [2] Juan Browne discusses the type and strength of the rock in one of his excellent videos about the Oroville crisis. [3] (Note that he demonstrates the weakness of the rock where he is standing, which is across the river from the spillway and might not be the same rock.) [1] http://www.mercurynews.com/2017/03/03/spoil-sites-for-oroville-dam-spillway-debris-hyatt-powerplant-starting-up-soon/ http://www.mercurynews.com/2017/03/03/spoil-sites-for-orovil... [2] https://www.youtube.com/watch?v=TpXtMZwpDqs https://www.youtube.com/watch?v=TpXtMZwpDqs [3] https://youtu.be/ilkU_ivYTqQ?t=679 https://youtu.be/ilkU_ivYTqQ?t=679

A failure of the emergency spillway could compromise the west side of the entire structure, no? What prevents that outcome?

by ubu7737 10y ago

A failure of the emergency spillway could compromise the west side of the entire structure, no? What prevents that outcome?

mikeash 10y ago

The base of the emergency spillway is bedrock, so it can only erode down that far. That's 30ft below the top of that spillway, which is why everyone talks about potentially having a 30ft wall of water hit downstream communities.

ubu7737 10y ago
I just watched Dept of Reclamation video on the designed failure of the Auburn Cofferdam. I get it now.
AnimalMuppet 10y ago
I'm not a geologist, but... Didn't the main spillway failure erode some of what was considered "bedrock"? Isn't the bedrock somewhat more erodable than the term "bedrock" would lead you to expect?
- mikeash 10y ago
  I'm not either, and I don't know! Total speculation: water partway down the spillway is considerably more violent than water just spilling over the top, so while bedrock may not resist the former, it can resist the latter. Another wild guess: the main spillway hasn't eroded any bedrock, just concrete, dirt, loose rocks, etc. If anyone actually knows versus my wild guesses, I'd be most interested.
- LukaAl 10y ago
  Don't know the details of the projects but from the pictures posted (here and elsewhere) it seems that only topsoil was eroded. Yes, bedrock is not indestructible, it could get eroded from water, but it takes times. Plus it get eroded slowly over time. The main concerns was the use amount of water released by the failure of the spillway. For sure the water keep flowing over the collapse spillway would erode the bedrock lowering it, but at a slower pace...
- tod222 10y ago
  Some…yeah, where some is the 1.7 million cubic yards of rubble now clogging up the Thermalito Diversion Pool. [1] When you look at photos or drone videos of the erosion near the main spillway, it's clear that an immense amount of rock has been eroded away (the color changes from brown to gray). [2] Juan Browne discusses the type and strength of the rock in one of his excellent videos about the Oroville crisis. [3] (Note that he demonstrates the weakness of the rock where he is standing, which is across the river from the spillway and might not be the same rock.) [1] http://www.mercurynews.com/2017/03/03/spoil-sites-for-oroville-dam-spillway-debris-hyatt-powerplant-starting-up-soon/ http://www.mercurynews.com/2017/03/03/spoil-sites-for-orovil... [2] https://www.youtube.com/watch?v=TpXtMZwpDqs https://www.youtube.com/watch?v=TpXtMZwpDqs [3] https://youtu.be/ilkU_ivYTqQ?t=679 https://youtu.be/ilkU_ivYTqQ?t=679