“It is important to recognize that during a rare event with the emergency spillway flowing at its design capacity, spillway operations would not affect reservoir control or endanger the dam,” wrote John Onderdonk, a senior civil engineer with FERC, in the Federal Energy Regulatory Commission’s San Francisco Office, in a July 27, 2006, memo to his managers.
“The emergency spillway meets FERC’s engineering guidelines for an emergency spillway,” he added. “The guidelines specify that during a rare flood event, it is acceptable for the emergency spillway to sustain significant damage.”
tl;dr: in case of flood, anything goes so long as the main dam wall remains functional?
Abrasion or corrasion - This is when large pieces of bedload material wear away the river banks and bed.
Attrition - This is when the bed load itself is eroded when sediment particles knock against the bed or each other and break, becoming more rounded and smaller.
Hydraulic Action - This is when the force of water erodes softer rock.
Solution or corrosion - This is when acidic water erodes rock."
So, there will be larger pieces of rock intake water that hit the bank of the spillway, slowly destroying it.
When engineering the spillway, you have to take that into account.
That means we have to accept that it will need repairs after use, just as a fire extinguisher needs it after use.
Since 19th century US has the most (well, at least a lot) dam failures.
Is it because there are so many? Are they privately owned and the owners just count on declaring bankruptcy if it fails? Is it the engineering, the geology, the maintenance?
The US is #2 in large dams with about 9,000. China is #1 with nearly 24,000, but their dam construction has almost all been since 1949. So my guess is that it's a combination of the US having many dams, and having had them for many years.
Well, it's always "different this time", because "newer designs".
Meanwhile countless tones of toxic waster from said reactors are also transported through regular highways and roads en route to disposal and/or are dumped in the sea by governments and "cheapest offer" subcontractors (including the mafia [3]).
Until sufficient solar and wind power generation comes online, I would rather we use nuclear and gas-fired power plants, and in that order. I think that on the balance nuclear power is cleaner. The sooner we get off fossil fuels, the better.
For nuclear incidents, I'm worried the next one will be in China, not in the states. China is building dozens of nuclear power plants, too quickly for the amount of trained technicians, critics say. There is also a disregard for nuclear safety standards. Last year there were 16 publicly reported incidents at Chinese nuclear power stations. According to RadioFreeAsia [1],
> Six [of the 16] incidents involved staff members breaching operational guidelines, and four were caused by a lack of internal communication. More worryingly, six were caused by staff members "pressing the wrong buttons."
which shows a lack of training. Another incident, described by the SCMP, tells how a critical alarm system was accidentally turned off 3 months before anyone noticed [2]
>An alarm system monitoring the radiation of reactor coolant at a nuclear power plant in Shenzhen was accidentally shut down for three months before the mistake was discovered, although a safety committee insisted the incident did not constitute a safety breach.
An official on the "Nuclear Power Station Nuclear Safety Consultative Committee" downplayed the incident saying "There was no harm done.", adding "there is always room for improvement for such a large operation."
"More worryingly, six were caused by staff members "pressing the wrong buttons."
I'm sure in one of the classic UI books (maybe Psychology of Everyday Things by Norman) there's a photo from a nuclear power plant, where there's two giant levers right next to each other, and the plant workers have attached a handle from a beer pump to one of them to distinguish it from the other, because as built they were identical and they kept pulling the wrong one.
edit: found a page referencing it, but the actual image has gone:
In the context of this Dam and other systems like nuclear power the fact that keeps coming home is that we (humans / our current culture) are generally bad at looking after systems over a long time.
I'd be money once this settles down, people will find and engineer report about this dam where someone recommends spending 100k on some detailed testing and some drilled cement injection to sure up the spill way. And then a week later they will find the minutes from the meeting were the administrators said the risk wasn't there so don't worry. Saved some money.
But nobody else would be so reckless to build nuclear power plants on the ring of fire, or in major hurricane areas.
Only Japan and the USA do. (Diablo, Fukushima, South Texas - even a crazy experimental one with overlarge vessels)
It's clear China has the exact issues you described. About half their nuclear power plants are in major typhoon areas; and plants in fujian and sichuan (totaling a half-dozen) are subject to major earthquakes.
As of midnight, the reservoir level was at 899.77 feet, and flow over the emergency spillway has stopped. If the level is above about 900 feet, the excess goes over the emergency spillway. Peak was around 902 feet. Data feed from dam sensors here: [1] Google Maps view of emergency spillway under normal conditions here: [2] Compare with drone footage from yesterday.[3] Main spillway (which has gates) is back in use.
The outflow seems to be the ~100000 cfs from the main spillway draining at full capacity, which they opened to 100% early in the evening to relieve the emergency spillway, in spite of the existing damage to the main spillway.
It's good to see the lake level coming down. 896 feet now, four feet below overflow at the emergency spillway.
Don't take the outflow rate number too seriously. The emergency spillway is just a concrete lip with no flow metering. Here's the actual data source information.[1]
From what I gathered the main spillway is quite damaged with a ~ 200' x 30' eroded hole in the center, potentially eroding into the supporting hill. It was a problem even before they doubled the outflow to 100,000cfs yesterday which I believe is still the current flow.
They want to get the lake down 50' to shutoff the spillway and assess repairs, but even at the current (high) release rate it appears they can only lower max ~8'/day, which is a problem because heavy rains return on Wednesday.
Let alone the emergency spillway, the main one's at risk too.
The spillway is kind of "around the corner" from the main dam, so I would guess the latter is probably not "doomed," at least at this point.
A realistic disaster scenario would be if the erosion retreats all the way back to the main spillway gates, or if it undermines the emergency spillway. The berm there would then fail, which holds back maybe 15 or 20 feet of lake altitude. A volume of water equal to that depth times the surface area of the lake would then exit over the hillside, completely uncontrolled. That would be more than enough to cause a serious downstream disaster.
The water flows would be very high (~a million CFS? total guess) which would cause even more severe erosion on that hillside. At that point the main dam might be at risk if the erosion traveled far enough laterally.
Indeed, 13 times more dams than France (who prides itself for 12% hydroelectricity), while USA is only 5 times bigger in population. China has the most number of large dams in the world: More than twice the USA, for 4x population.
This is what California always does. We forget about what happens in a drought as soon as the rain comes, and as soon as the rain comes, we realize we forgot about what happened the last time it flooded. After the catastrophe is already upon us, recriminations fly, trillions of pixels are wasted on heavy-handed think pieces, and we forget again, only to wonder why an entirely preventable tragedy managed to find us the next time one comes.
Outrage and complaining is much easier than action.
During the drought, the best thing we got for legislation to 'fix' it, was preventing people from getting water without explicitly asking at restaurants. As idiotic at this was (this accounts for approximately 0.0% of water use in California), activists rejoiced over how they were fixing the problem by having everyone 'chip in'. Meanwhile farmers continued on not even paying for the water they use (farming is >50% of water usage).
One almond requires over a gallon of water, and you can buy a pound of raw almonds for $8 or so at my grocery store. But that 1/16 gallon glass of water is gonna save the day.
Meanwhile, our state capital is -- wait for it! -- building out water meters so they can tell how much each house is using. They're trying to get 80% of households by 2025.
Indeed, and in Australia too, but even sillier in floodplains you see a few very old houses built on stilts seemimgly floating above flood waters and next to them suburbs of roof tops of submerged modern houses built for miles around.
It's a human thing. In the east-south of Spain have floods from storms almost every few years , but instead of have things prepared for those, they get the money from insurance and let everything as it was, they don't fix the drain/sewage systems they keep building in same natural water ways. So every few years happens the same and they cry every time.
While true, there has also been a tremendous amount of work done on flood control, levees and so on in the Sacramento/delta areas that flooded in 1997. Time hasn't been entirely wasted.
It reads like they designed the spillway to withstand this much water, provided that the ground it rests on doesn't move.
Was it a sink-hole under the spillway or the force of water broke the concrete and then created the hole?
My understanding from this accident and the Glen canyon dam accident, is that they are not very good at concrete in contact with rushing water.
In this last instance, the rushing water is eroding the dirt under the emergency spillway so it will end up forming a bridge. the emergency spillway is a mini-dam, it will just fall if it's not supported. And if it falls, the rushing water will erode the rest of the dirt, lower and lower. The worst case scenario is a complete dam accident (uncontrolled drainage of the lake) that would not even involve the actual dam.
I'm not sure about the specific location of said complex, but the Sutter Buttes in general - being buttes - are at a much higher elevation than the surrounding portions of the Central Valley.
Holy shit look at the pictures. Both the regular and emergency spillway are heavily damaged and even more rain is expected Tuesday and in the coming weeks.
They shut the main spillway off because of damage and now they're running it at maximum flow because the emergency spillway is even more damaged. This feels every bit like a hail Mary pass to drain the lake as much as possible before the dam breaks. In another day or two they won't have any spillway left.
This dam is doomed, it seems like one of the rare times media is downplaying the risk... Probably because a lot of people are going to die :(
If the emergency spillway goes, that's 30ish lake-feet of water that would drain uncontrolled. That would likely wipe out a few towns down the river.
I think gp was getting to the fact that the main spillway is eroding as well, and it could reach a point where it was unusable. In that case, with significant rainfall expected in the next week and a good deal of snow melt to follow, there could be huge amount of water coming into the basin with no way to control the outflow, which could result in much worse flooding.
Hopefully that all can still be avoided. It's a bit dramatic to say it's inevitable. It's a possible scenario, but it's also possible the right plan avoids it.
The emergency spillway was used because the main one was already badly damaged so they shut it off. Now they're saying the damage to the emergency spillway is even worse than the main spillway so their turning the main spillway on full tilt to drain below the level the emergency spillway activates.
The thing is... They drained below the emergency spill way level many hours ago and it's off, but they're still running the heavily damaged main spillway at full tilt. I think it's a last ditch attempt to drain the lake before the dam fails, they just don't want to say it because everyone will panic
This whole emergency evacuation makes no sense to me. They cut the flow on the main spillway from 100,000 to 50,000 cubic feet per second to push water to the emergency spillway and it immediately started dangerously eroding at only 6,000 to 12,000 cfps. So they cranked the main spillway back up to 100,000 cfps and as I type this the water level has dropped back down well below the top and the erosion danger has passed. The damage on the main spillway looks severe but not at immediate emergency levels. But in the mean time they have unnecessarily caused panic among 180,000 people with no warning and generated national headlines. It just seems like a lot of overreaction.
> they have unnecessarily caused panic among 180,000 people
Hindsight is 20/20. If the dam had failed, people would be saying "they unnecessarily killed 180,000 people because they were too lazy and politically timid to order an evacuation."
It's like tuning sensitivity vs. specificity in medical tests. In this case the cost of a false negative (thousands of deaths) is a lot higher than the cost of a false positive (a few days of disruption). So the threshold is set low so as to minimize the total expected cost, summing probability of outcome * cost to society. Perhaps counterintuitively, the goal is not to minimize the odds of being wrong.
We should expect to see more false positives than false negatives. If it were any other way, the system would be working sub-optimally.
The damage to the main spillway is extreme. Look at the pictures, it's more of a semi controlled waterfall at this point. If erosion moves upstream on the spillway, which it eventually will, once it reaches the gates they will need to stop the spillway or risk the dam itself.
Their emergency spillway is already unusable, so this means just get everyone out and wait for the dam to blow once the main spillway erodes too far back
They didn't (and still don't) know the full extent of the damage to the concrete emergency spillway structure. If it failed, the areas evacuated would flood. It's still possible it might fail, they really won't know until morning.
The concrete spillway is the main spillway. The emergency spillway is a concrete lip draining onto an unpaved hillside. It was partly because of the damage to the main spillway that they allowed the lake level to rise to the level of the emergency spillway, but when it appeared to be eroding alarmingly quickly, they opened the main spillway 100% in spite of knowing the lower half was already severely damaged.
“The emergency spillway meets FERC’s engineering guidelines for an emergency spillway,” he added. “The guidelines specify that during a rare flood event, it is acceptable for the emergency spillway to sustain significant damage.”
tl;dr: in case of flood, anything goes so long as the main dam wall remains functional?