In reply to nutherjrfan:
It was the I-35 Bridge in Minneapolis.
Yes initially it was blamed on age and then they found that the gusset plates were to small for the increased capacity that the bridge received over the years. However, that bridge stood for 40 years. Went through 40 years of inspections and no one ever caught that.
Age definitely came into play to some respect, but doesn't take away that much of our infrastructure is still aging.
golfduke wrote:pinchvalve wrote: How close to the dam do people actually live? Why would anyone buy a house situated just downstream of a massive earthen dam that is really, really old in a state known for earthquakes? You'd think it would already be a ghost town down there.I'm not an expert, but they're evacuating everyone downstream on the river. It's not a concern of dam breaching, but more of an uncontrolled flooding along the riverbanks... They're evacuating several miles downstream, so it's possible that even considering this is a 100 year weather pattern, the potential for flooding in this area was presumably pretty low to begin with. Basically, something something it's a complex sequence of unfortunate events that leads to catastrophe rather than a single, defined issue.
Correct. Fema floodzones dont take into account a dam possibly failing and releasing a ridiculous amount of water.
As I recently found out, these are called dam breach inundation zones, and unlike the fema floodzones, your homeowners insurance policy will not require flood coverage, but it is optional.
We are at the fringe of a dam breach inundation zone, downstream of a relatively small lake with a relatively brand new dam. And I only found this out because I found the info on the county gis mapping site. I am sure the sellers of our house had no clue. My realtor who is also a surveyor also had no idea.
My guess is at least some of the folks being evacuated may not have known they could have been impacted either.
For fun, I checked the flow in the Colorado River near my house today. 4450 cfs right now. This spillway is dumping 150,000 cfs.
Downtown Oroville is a few miles downstream of the dam. It is protected by levies, but with the amount of water being released out of the spillway, there isn't much margin. About 15,000 people live in Oroville, so a small portion of the 200,000 people being evacuated. A lot of those people live above the lake as well.
The main spillway appears to be completely destroyed from that initial hole down, the water has eroded everything away. I am curious to see what it looks like once this whole thing is over.
I grew up in Oroville, and spent my summers on that lake, I still have a lot of family there. Fortunately they have all evacuated and are fine.
As far as the roads above the lake, yes they are amazing. I am convinced this part of California could go toe to toe with anywhere else in the US as far as driving roads go.
What's the largest size available?
mad_machine wrote:Flight Service wrote:from what I understand, they put out a call to FEMA and have not heard a thing back.Grtechguy wrote: I wonder if this will change their mind about succeeding from the union with a FEMA call.Given the recent response in other states, it might just stiffen the resolve to leave. That is a big hole.
Same thing happened in Louisiana after the recent tornados...Nothing.
BrokenYugo wrote:tuna55 wrote: Running at "full tilt" is probably not the best scenario for flowing water. Why not freewheel the turbine and just use the generator to regulate the RPM to whatever the overspeed limit for those things?I would assume the turbine has to run at a precisely set RPM to spit out 60 HZ three phase power.
Undoubtedly they are designed to spin at 3600 RPM.
However, they probably can spin to 3960 without too much trouble, and just use the grid to slow it down.
It might not be that modern, but if I was designing a hydroelectric control system, it would seem reasonable to include an operation like that. It would sort of provide a "something has gone terribly wrong and now this dam needs to push as much water through it as possible and forget about making power".
Wind turbines do this, for much more obvious reasons.
Keith Tanner wrote: For fun, I checked the flow in the Colorado River near my house today. 4450 cfs right now. This spillway is dumping 150,000 cfs.
Google says the Mississippi River is 600,000 CFS at the gulf of Mexico.
Latest pics of the Emergency Spillway. That wash out hole got really close to the toe of that wall.
tuna55 wrote:BrokenYugo wrote:Undoubtedly they are designed to spin at 3600 RPM. However, they probably can spin to 3960 without too much trouble, and just use the grid to slow it down. It might not be that modern, but if I was designing a hydroelectric control system, it would seem reasonable to include an operation like that. It would sort of provide a "something has gone terribly wrong and now this dam needs to push as much water through it as possible and forget about making power". Wind turbines do this, for much more obvious reasons.tuna55 wrote: Running at "full tilt" is probably not the best scenario for flowing water. Why not freewheel the turbine and just use the generator to regulate the RPM to whatever the overspeed limit for those things?I would assume the turbine has to run at a precisely set RPM to spit out 60 HZ three phase power.
Most hydroelectric plants spin at significantly lower speeds, 900-1200rpm, and have multiple poles in the rotor. Trying to run the units faster while hooked to the grid is like trying to get one of the three locomotive engines on a big train to go faster than the other two; it just doesn't work that way. Wind turbines are often times induction generators instead of synchronous generators, which is an entirely different technology and why they can run at different speeds.
oldopelguy wrote:tuna55 wrote:Most hydroelectric plants spin at significantly lower speeds, 900-1200rpm, and have multiple poles in the rotor. Trying to run the units faster while hooked to the grid is like trying to get one of the three locomotive engines on a big train to go faster than the other two; it just doesn't work that way. Wind turbines are often times induction generators instead of synchronous generators, which is an entirely different technology and why they can run at different speeds.BrokenYugo wrote:Undoubtedly they are designed to spin at 3600 RPM. However, they probably can spin to 3960 without too much trouble, and just use the grid to slow it down. It might not be that modern, but if I was designing a hydroelectric control system, it would seem reasonable to include an operation like that. It would sort of provide a "something has gone terribly wrong and now this dam needs to push as much water through it as possible and forget about making power". Wind turbines do this, for much more obvious reasons.tuna55 wrote: Running at "full tilt" is probably not the best scenario for flowing water. Why not freewheel the turbine and just use the generator to regulate the RPM to whatever the overspeed limit for those things?I would assume the turbine has to run at a precisely set RPM to spit out 60 HZ three phase power.
ok, fair point.
For the record, I work on steam and gas turbines every day. They are always synchronous in my world, though smaller units are geared.
I made the reference to wind for a different reason that I guess was not evident. They have overspeed protections because the wind speed can be higher than they are capable of dealing with. They can and have failed by cutting down their own towers in high winds. Hence, they have methods of reducing the RPM which are actually quite involved.
The point was, regardless of what RPM they are designed to run at, they can undoubtedly go faster due to natural design around grid fluctuations and trips. I would assume a control scheme exists for a more long-term run at that higher RPM for purposes of draining water rather than producing power.
Some good videos with good perspective.
From 2/13 Tues, good control.
https://www.youtube.com/embed/VBP-4ah3U6s?list=PLeod6x87Tu6eVFnSyEtQeOVbxvSWywPlx
From 2/12, out of control.
https://www.youtube.com/embed/T5zumuQIMV0?list=PLeod6x87Tu6eVFnSyEtQeOVbxvSWywPlx
Taken from here
From 2/11
https://www.youtube.com/embed/bephol1Ormg?list=PLeod6x87Tu6eVFnSyEtQeOVbxvSWywPlx
Tuna: The units can't get faster than synchronous speed while hooked up to the grid unless the entire grid goes to a higher frequency. The only way to spin the units faster would be to spin them disconnected. Spinning them disconnected is like revving an engine in neutral; sure you can spin it right to the red line, but you won't be using fuel or air like accelerating the car would use. The wicket gates for those units are going to be wide open at full power operation and nominal rpm. Adding more water would overload the electrical end of the generator before it will speed up.
If they wind gets to be too much for the turbines we control they usually turn out of the wind to maintain speed. If it gets too cold, though, they just drop out and lurch the grid for the MW they were supplying.
In reply to JohnRW1621:
Those are some interesting videos.
Especially seeing the parking lot become part of the reservoir and the emergency release area. Wow.
Also- Keith posted the flow of the Colorado River, and that has the power to make the Grand Canyon. Water at that high of volume is very strong.
In reply to alfadriver:
After watching those videos, I said, "wow, water is a powerful earth mover." 
alfadriver wrote: In reply to JohnRW1621: Those are some interesting videos. Especially seeing the parking lot become part of the reservoir and the emergency release area. Wow. Also- Keith posted the flow of the Colorado River, and that has the power to make the Grand Canyon. Water at that high of volume is very strong.
To be fair, it's winter 
I think the normal flow is closer to 22,000 cfs.
My personal frame of reference is the Ottawa river. I've spent a lot of time kayaking on the massive hydraulic features of that waterway, which are almost all caused by flow instead of obstructions. It's a rowdy one at times. Apparently it averages around 69,000 cfs. Having more than twice that coming down a spillway is amazing.
oldopelguy wrote: Tuna: The units can't get faster than synchronous speed while hooked up to the grid unless the entire grid goes to a higher frequency. The only way to spin the units faster would be to spin them disconnected. Spinning them disconnected is like revving an engine in neutral; sure you can spin it right to the red line, but you won't be using fuel or air like accelerating the car would use. The wicket gates for those units are going to be wide open at full power operation and nominal rpm. Adding more water would overload the electrical end of the generator before it will speed up. If they wind gets to be too much for the turbines we control they usually turn out of the wind to maintain speed. If it gets too cold, though, they just drop out and lurch the grid for the MW they were supplying.
I promise I understand this.
I also understand that they can most likely use the grid as a break to avoid overspeed and let them freewheel, at least that's what I would design.
Given the location, these few days of unregulated hydraulic mining should result in more than a few bits of found gold for some lucky explorers, though I'm sure that access to the downstream area will be heavily restricted.
No matter how much humans try to harness Mother Nature, she always wins in the end.
Reading here: Dam the power plant was shut down early Friday due to debris and sediment blocking the waterway, which could have contaminated the power plant. Looks like they can't restart it until the waterway below the dam is cleaned out.
For comparison purposes, Niagara Falls normally flows less than 100,000 CFS, although that's a variable number depending on the time of day.
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