Posted on 02/12/2017 4:26:47 PM PST by janetjanet998
Edited on 02/12/2017 9:33:58 PM PST by Admin Moderator. [history]
The Oroville Dam is the highest in the nation.
A couple of questions.
In Juan’s update 3/17 that shows the re-start of the spillway,
https://www.youtube.com/watch?v=kQe0J5NLLT4 he apparently was told that 40,000 cfs was the max safe flow right now although the spillway was built for a capacity of around 150,000 cfs. That’s a little less than a third capacity it can run right now.
1) Question: What was the actual sustained top flow rate on the main spillway during the February 2017 time-frame when basically all hell broke loose?
2) Question: If they were able to effectively repair and seal off the upper portion of the spillway, could a viable alternative be to simply get rid of the remaining lower spillway and the debris down to the bedrock below the upper spillway and let the water free-fall from the upper spillway onto and through the bedrock to the river below, a bit like it’s doing now but after all the non-bedrock is cleared?
1) if my memory is correct the flow was at 50,000 cfs and in the process of ramping it up to 70,000 when the first pieces started to fly off
2) I’m not sure. But I don’t know what the “bedrock” is and I don’t think they do either. It looks to me the flow cut a channel into the “bedrock” on the right side and was getting deeper each day. So even the “bedrock” can still be eroded away over time
They did go to 100,000 after the “emergency” spillway erosion issue took place, just to get the water levels down in the lake (they were at 901 feet, the spillover level for the emergency weir). But it’s been to 150,000 in past years. I remember seeing a chart that showed that it could (or should have been able to) pass over 250,000 with the gates wide open, but that there were concerns downstream with flooding and overburdening dams further down.
In its damaged state, 50,000 was quoted as the max and 40,000 was considered the minimum sustainable level. At more than 50,000, they were concerned with additional damage, and at under 40,000, the water spill off the end of the spillway would be too vertical and would tend to undermine the end of the spillway.
I had thought that they were going to lay down a hardened, sloping surface at the end of the remaining spillway to allow lower flows, but they did not do that. They, instead, will run it in the 40-50,000 range for a few days, then shut it down for a few weeks and rely on the power plant to pass water downstream. In the press briefing, they said that there would be roughly 3 major releases to accommodate the spring melt, after which the Hyatt power plant in the dam could maintain flows adequately.
Bedrock is essentially that blue/gray rock that you see exposed. It is much harder than the looser brownish rock above it, and makes a pretty sturdy stream bed. It is at the bottom of the “plunge pool” where the spillway dumps water down, and provides a path all the way down to the river. Most of the softer dirt and rock has been scrubbed away from that path already, and was what made up the bulk of the debris pile they cleaned out of the river over the last couple of weeks.
February 7: As water releases from the flood control spillway ramp up to 54,500 cubic feet per second (cfs), in anticipation of inflows expected from rainfall, DWR employees notice an unusual flow pattern. Spillway flows stop for investigation. Engineers find large area of concrete erosion.
Nice graphic. A few of more questions:
1) Do you know when prior to Feb 2017 the spillway outflows were significantly greater than 50,000 cfs? Did they ever previously run the outflows at full capacity of 150,000 cfs?
2) Any educated guesses as to why there was damage at 50,000 cfs now and not after outflows were significantly greater? (Maybe the one-two punch of first weakening and then later, final breaking - and/or - the constant battering of hot/cold expansion/contraction pressure on the concrete over about 50 years?)
3) I've heard some experts call this one of the greatest engineering failures in history. Maybe that's too much, I don't know, but how do you rate the failure of the spillway after it ran for 24 hrs at about one-third capacity its planned capacity?
low bid?
As ER333 has pointed out, the undermining due to the flawed drainage system design produced (a) thinning leading to diagonal cracking that keeps getting worse, (b) voids under the slab due to wash-out which now hold more water for more washout, etc etc [except where voids are filled in recent repairs] and (c) the spillway walls were not ripped out previously and now the outflow has potential damage every time it is ramped up. (d) I think we are also seeing a further compromised underslab drainage system itself, water release may occur without the full release of pressure.
Hi Meyer, just for discussion...if they weren't able to seal effectively near the top of the spillway (near the gate region), then the first set of drains "output" should reveal this (each set of drains sequentially service a section of the spillway).
Regarding "less flow": Until the "drains" flow is reduced to a trickle, hydraulic jacking may create net forces upward greater than the weight of the water. Even when slabs were rebar anchored in the blue/grey hard amphibolite bedrock, the slabs revealed consistent fractures along the concrete flexure "weak point" of the drain lines (post 2,421). This reveals the power of hydraulic jacking forces.
The rock bolt array emplacement is in rock that reveals as "weathered" (fractured & weaker than the hard amphibolite). There is a reason why DWR is saying “what you see today may not be there tomorrow”..
My keen interest in the upper main spillway is from the depth of weathered rock revealed from the Emergency Spillway erosion. This weathered rock depth (to an elevation) was adjacent to the head of the gate outlet area of the main spillway. Archive documents confirm this similar geology where it is stated that there are sections in the upper main spillway that are emplaced upon "lesser quality rock".
I believe they have adequate monitoring to be able to respond to any sudden anomalies. If nature cooperates, they have windows of time for repairs. However, in engineering, you become accustomed to Murphy's law...
So maybe, due to the flawed drainage system design, the one-two punch of initial weakening in earlier, higher outflows, and then later, final breaking at much lower outflows.
According to this, they operated at 160K cfs in 1997.
http://www.chicoer.com/article/NA/20170218/LOCAL1/170219704
“The weather this year, as bad as it seems, was much worse in 1997. There was a one-week period where everything was flooded.
People were being evacuated in Tehama, Hamilton City, Durham, Yuba City and Marysville. Butte Creek cut a new channel in the canyon. Highway 70 above Lake Oroville was badly damaged. No valley communities were spared. Roads, bridges and a section of railroad were washed away. It was relentless.
The inflow to Lake Oroville on New Year’s Day was 328,000 cubic-feet per second. By comparison, the peak inflow to Lake Oroville this month was 190,000 cfs.
The outflow in 1997 was 160,000 cfs. The peak last week was in the neighborhood of 110,000 cfs.
The difference, of course, is that in 1997 the spillway wasn’t broken.”
IMO, it wasn’t an engineering failure. It was a lack of proper preventive maintenance that caused the problem. Most concrete highway paving would last much longer than it does, if joint maintenance were done adequately.
But guess what gets cut when money’s tight? Maintenance. Governments never, ever cut payroll, they cut projects or material.
There’s never money to maintain, but endless funds to fix stuff once a catastrophe occurs.
“when prior to Feb 2017 the spillway outflows were significantly greater than 50,000 cfs?”
It was a very long time ago.
I checked releases since the 2013 repair to the spillway and a couple were 13,000 cfs, but all the rest were much, much lower. This was the first ‘test’ of the repair.
In all this heavy talk of the spillway’s ‘faulty’ drainage system it’s important to remember that it wasn’t designed to handle the water leakage from an unmaintained, cracked surface.
There is a bigger engineering picture here that frames the question on the "rating of failure". In this "picture" is the sequence of engineering judgements and events that continued in the face of stark evidence where other dam spillway designs have failed. I haven't put together the full sequence in a single post - only pieces of the whole story & history. Remember this dam was intended to sustain 1861/1862 flood scenarios.
Just a few notable points... the flood capacity of the combined spillway design was intended to handle "standard project flood" conditions of input rates of 440,000 cfs, by designing & rating the total combined spillway capacity of the dam at 646,000 cfs.
+Emergency Spillway stated design rating: 350,000 cfs. Failed. It couldn't sustain a meager 12,000+ cfs.
+Main Spillway stated design rating: 296,000 cfs. Failed. Blowout at 55,000 cfs.
In Engineering, designs have safety factor ratings (Factor of Safety FoF or Safety Factor SF) that are higher than the stated specifications (i.e greater than 1). IN the case of the spillways, this would translate into structural integrity greater than the stresses placed from the design rating - including knowing the erosion performance of the geology in the case of the emergency spillway.
One way of comparing the magnitude of failure: Right now the only operating spillway is damaged & limited to 50kcfs. This is a far sight short of a 646,000 cfs designed rating. In such high impact structures such as dams, there are no excuses. You must know its performance and be darn sure any unknowns are proven out. btw- They had later knowledge of failure modes after dams failed & they had time to evaluate/fix these issues in their spillway. This too should be factored into the failure consideration of "engineering judgement".
So more along the lines that maybe due to lack of proper preventive maintenance, the constant battering of hot/cold expansion/contraction pressure on the concrete over about 50 years caused the failure.
You know, it’s interesting about preventive maintenance (PM) and government. My experience is that it is sometimes hard to get a private enterprise to diligently perform PM especially if the thing needing PM is somewhat peripheral to the purpose of the company.
Same but worse in government because no one in government really owns anything. It’s all someones else’s money (so nobody cares that much about waste) and the assets belong to “government” but no one in particular. Hence things like run-down “projects” neighborhoods, post offices and DMV buildings and equipment. One of the federal government’s few valid activities is military for defense. I would say that the feds are best at maintaining those assets because maintaining the military is a main constitutional purpose of the feds. Even then, they have their problems.
I don’t see how a project like the Orville Dam could become a profitable enterprise for some company to take over and run. If so, at least someone would have a sense of ownership.
ORDERED, yep.... Yet I bet there will be a lot of people who won’t evacuate, who’ll cry, why sisnt anyone come to save us.
Been there, done that. I spent my whole 35 year working career in private industry. Wood products, sawmills, paper, plywood, etc. Trust me, the same thinking permeates production mentality. I understand that there is a balance, but invariably, the engineering/maintenance types never become the plant managers. Only the production types. Run it 'till it breaks, then lay the blame on the engineers and millwrights.
As for government, the goal isn't a proper operation, or maintenance, or public service. The goal is for each and every "public servant" to reach that pot of gold at the end of the rainbow: a retirement that never runs out of money and a gold-plated medical plan that completely pays for every drug and medical procedure, no matter the cost.
Most of the failures we are seeing are not in the performance of the original construction of the dam or in the patchwork ordered at various times.
Instead, I see deficiencies in the original under-slab spillway drain details and deficiencies in the design and management of periodic maintenance.
Well, another difference between a private enterprise running the show and government running the show - corrective action. In government no one is really accountable. And if someone were accountable in a case like this, they're long gone. I mean, nobody in government actually "owns" the Orville Dam and it is built and maintained entirely with other people's money.
If it were somehow profitable and feasible for private enterprise to own the dam, at least somebody would have ownership and it would be their own money on the line to keep it maintained.
Bingo.
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