houstonscott
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Evacuate and hope for the best. Texas will sell you electricity but you have to pay this time...
California Drought
- Thread starter NoTrespassing
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orezok
Super Member
Thanks for your compassion.
dragoneggs
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That was a bit insensitive considering the circumstances...
ultrarunner
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23 million people get water from the Oroville dam...
The area under the dam has a lot of low lying sections and 100k have been ordered to evacuate.
The aerial views show traffic backed up for miles.
Wondering if they couldn't use both sides to evacuate like they do in Hurricane areas?
More rain forecast later in the week.
Optimal fill capacity is around 70% due to seismic concerns... it is over 100% now.
The area under the dam has a lot of low lying sections and 100k have been ordered to evacuate.
The aerial views show traffic backed up for miles.
Wondering if they couldn't use both sides to evacuate like they do in Hurricane areas?
More rain forecast later in the week.
Optimal fill capacity is around 70% due to seismic concerns... it is over 100% now.
aczlan
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California
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I've tried to use that twice this evening but either it doesn't have any soil data (its too steep and rocky for farmland) or I'm missing something. Did you get it to work? The address there is Oroville Dam, CA (not visitor center). It centers a satellite photo there, but there's nothing but instructions in the data box that says 'your result will appear here'. What don't I know?
farmer2009
Elite Member
Try the state and county tab.
I just entered Butte county California and then zoomed in on the lake dam. Drew a AOI around the dam area I drew was about 800 acres. Went to soil map and found a 155 acres of dam area. The failed primary spillway is built on 2 soil types. 553 & 554. Both are Dunstone-Loafcreek. Just different slopes. Although it seems the failure happened close to the land classification switch. 554 shows bedrock at 15-47 inches. With a gravelly loan above it. First restrictive layer is at 10-20 inches as a paralithic bedrock and a lithic bedrock at 20-40 inches.
Now I'm not a soils engineer so some of what I wrote I can't explain. But it seems like there's not a lot to erode before bedrock. Which should mean it'll look really nasty real fast but then stabilize.
I hope they are wrong about the emergency spillway and everything is just precautionary.
Larry Caldwell
Super Member
The engineers on site think the ground dried out and shrunk during the drought, leaving the concrete unsupported.
Raspy
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The regular spillway problems are no big deal. Yes, there will be more damage to it if they keep using it, and it is severely damaged, but they must keep using it and it's failure doesn't threaten the dam.
The bigger issue is the emergency spillway. As the water pours over the top it erodes the sloping hillside that the water pours onto. The parking lot next to the emergency spillway is also overflowing down the same hill.
The cascade of water is cutting deeply into the dirt slope and the cut is undercutting backward and upward toward the emergency spillway. It appears to be just mountain dirt. If this undercutting undermines the emergency spillway, it will fail and open up a port to the lake from underneath. Then the erosion from lake water will cut a channel that will begin to drain the lake. That will be uncontrollable and devastating.
They are currently sandbagging (with some kind of giant bags filled with rocks) the undercut to try to stop it as the regular spillway is open for business and getting the emergency overflow stopped.
No big deal how much damage occurs to the regular spillway as long as it can lower the lake level and I read they have increased the flow to about 100,000 cfs to do just that.
Early on in the regular spillway failure, there was a lot of mud being scoured out and flowing down into the river. Then the water cleared up and they announced the cut had reached "bedrock". Whatever that material is, it's not just soft dirt and it's much harder to cut. That's reassuring and will allow them to open the gates for max flow to save the emergency spillway from being undercut.
Overall, it's a poor design where an overflow can cut soft ground and lead to a catastrophic failure.
If there is a major failure it probably won't be for another week or two. By then everyone will be back in town!
This is going to be a very expensive re-design and fix. The scale of it is really impressive. That spillway looks small in pictures, but it is huge in person.
The bigger issue is the emergency spillway. As the water pours over the top it erodes the sloping hillside that the water pours onto. The parking lot next to the emergency spillway is also overflowing down the same hill.
The cascade of water is cutting deeply into the dirt slope and the cut is undercutting backward and upward toward the emergency spillway. It appears to be just mountain dirt. If this undercutting undermines the emergency spillway, it will fail and open up a port to the lake from underneath. Then the erosion from lake water will cut a channel that will begin to drain the lake. That will be uncontrollable and devastating.
They are currently sandbagging (with some kind of giant bags filled with rocks) the undercut to try to stop it as the regular spillway is open for business and getting the emergency overflow stopped.
No big deal how much damage occurs to the regular spillway as long as it can lower the lake level and I read they have increased the flow to about 100,000 cfs to do just that.
Early on in the regular spillway failure, there was a lot of mud being scoured out and flowing down into the river. Then the water cleared up and they announced the cut had reached "bedrock". Whatever that material is, it's not just soft dirt and it's much harder to cut. That's reassuring and will allow them to open the gates for max flow to save the emergency spillway from being undercut.
Overall, it's a poor design where an overflow can cut soft ground and lead to a catastrophic failure.
If there is a major failure it probably won't be for another week or two. By then everyone will be back in town!
This is going to be a very expensive re-design and fix. The scale of it is really impressive. That spillway looks small in pictures, but it is huge in person.
Last edited:
California
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That makes sense. I think the photos we saw of them a year or so ago inspecting minor water coming up from beneath, indicate there might also have been erosion below, leaving it unsupported over a void.
Then - another theory that would be interesting to investigate: over on Metabunk (referenced above) one poster declared he understood standing waves in electronics and electrical transmission, said similar physics can occur in fast-moving water, and he speculated this may have caused unanticipated stresses over an unsupported portion of the spillway. So the design may have been sufficient to span a void but before considering the added uneven stress of standing waves in the water channel. Interesting theory. I'll be interested to see if we hear more about this.
