GOVERNMENT!! FUCK YEA!!
Oroville Dam: Feds and state officials ignored warnings 12 years ago
31–40 of 64 posts
Re: Oroville Dam: Feds and state officials ignored warnings 12 years ago
#32From 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.
Re: Oroville Dam: Feds and state officials ignored warnings 12 years ago
#33This 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 pass…
> 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.
Re: Oroville Dam: Feds and state officials ignored warnings 12 years ago
#34This 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 pass…
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.
Re: Oroville Dam: Feds and state officials ignored warnings 12 years ago
#35From 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 lo…
I get the feeling the dam is likely doomed and they're trying to drain the lake as much as possible to decrease the force of a break
Re: Oroville Dam: Feds and state officials ignored warnings 12 years ago
#36This 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 pass…
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 to…
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Re: Oroville Dam: Feds and state officials ignored warnings 12 years ago
#37This 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 pass…
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.
Re: Oroville Dam: Feds and state officials ignored warnings 12 years ago
#38I was just wondering about it the other day while researching the topic: why are there so many dam failures in the states? https://en.wikipedia.org/wiki/Dam_failure#List_of_major_dam_... 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…
I don't know. However, construction projects with ridiculous levels of corruption are not unknown in America.(1)
Re: Oroville Dam: Feds and state officials ignored warnings 12 years ago
#39From 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 lo…
I get the feeling the dam is likely doomed and they're trying to drain the lake as much as possible to decrease the force of a break
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.
http://www.icold-cigb.org/article/GB/world_register/general_...
Re: Oroville Dam: Feds and state officials ignored warnings 12 years ago
#40Earlier quoted context omitted.
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.
Right. That concrete lip is holding back about 30 feet of water, which is what they feared could be released if it collapsed.