Moderators: richierich, ua900, PanAm_DC10, hOMSaR
dc10lover wrote:Do you have a source for the 14" of rain prediction? I haven't seen anything like that.Californis is expecting 14" of rain through March. I think people in Sacramento, California need to be ready to evacuate. Officials are not expecting Oroville Dam to make it. Plus the mountain snow runoff will not help. Please watch youtube videos and such to keep up for the latest.
Thanks
einsteinboricua wrote:The dam itself is structurally sound and officials are not concerned about its integrity.
What concerns officials are two things:
1. The primary spillway has a sinkhole which opened up last week. To keep pumping water down that spillway means eroding the sinkhole and making it bigger.
2. The emergency spillway is really just an overflowing wall to allow excess water to go down if the primary spillway cannot pump water fast enough. However, with the recent usage, terrain began crumbling away. If it continues to erode, the wall could collapse and send a 30ft surge of water down the hill in an uncontrolled manner. Oroville and nearby towns would definitely be destroyed if that happened. Sacramento? They probably won't feel a thing: there are many bypasses designed to take on some of that flow.
Officials over the weekend had their hands tied: do they shut off flow to the primary spillway and allow water to go through the emergency spillway (eroding the structure) or do they open the primary spillway and take the risk of destroying the primary spillway altogether?
There is rain in the forecast so officials are trying their best to pump out enough water so that the expected inflow does not merit the use of the emergency spillway or maybe even the primary spillway. That would allow officials to begin repairs, at least temporarily, until the dry season hits.
The dam is safe, Sacramento is safe, even Yuba is safe.
wingman wrote:It pains me somewhat to say it but Trump is right about our infrastructure problem
salttee wrote:Here is the main spillway damage.
einsteinboricua wrote:It has since extended to the other side.
WarRI1 wrote:That is scary. This is the first pictures I have seen of the damage to the spillway. Is the danger from a collapse of the upper wall because of undermining the dam wall itself?? It looks possible if the whole hill collapses.
wingman wrote:It pains me somewhat to say it but Trump is right about our infrastructure problem.
rfields5421 wrote:Oroville has not demonstrated an infrastructure or design failure.
salttee wrote:rfields5421 wrote:Oroville has not demonstrated an infrastructure or design failure.
How can you say that? The spillway is a part of the dam, you can't build a dam without some way of discharging water.
The spillway failed didn't it?
salttee wrote:rfields5421 wrote:Oroville has not demonstrated an infrastructure or design failure.
How can you say that? The spillway is a part of the dam, you can't build a dam without some way of discharging water.
The spillway failed didn't it?
Tugger wrote:salttee wrote:rfields5421 wrote:Oroville has not demonstrated an infrastructure or design failure.
How can you say that? The spillway is a part of the dam, you can't build a dam without some way of discharging water.
The spillway failed didn't it?
But that is not due to design. It could be just a mechanical failure or construction flaw that became a failure event under duress of the current weather conditions.
Tugger wrote:I will note that the main spillway is built on bedrock, the bedrock the dam is anchored with. The hillside foundation beneath is won't erode to failure but the damage will be extensive.
Tugger wrote:Roughly the real problem is that the inflows to the reservoir are going to (and have been) exceed its maximum outflow capacity (which is exasperated by other outside factors,there are powerline towers that may be eroded), necessitating the use of the emergency spillway, and the emergency spillway is not on bedrock and the concrete apron is not cover enough ground to prevent erosion back to the reservoir itself. The inflows are expected to be potentially 250,000 cu ft/sec while the main spillway is normally a max of 200,000 but is currently limited to 100,000.
rfields5421 wrote:In a strong enough flood, the goal is to contain the damage to the expected area and prevent a catastrophic failure of the dam.
rfields5421 wrote:Actually airliners are built to a standard which will allow the wings to fall off in certain conditions. If they were built to a never ever possible for the wings to fall off - they would not be able to fly. They would weigh too much.
All engineering is to a standpoint where the risk of failure is minimized. It is ALWAYS a cost/ benefit decision. Yes, this is too often to a risk point others might/ do find unacceptable. And Monday morning quarterbacking is the basis of much of the US legal system.
Dams are designed to not fail, but engineers also design to deal with the possibility that the inflow of water might exceed the capacity of the base spillway system.
.......
rfields5421 wrote:The current issues with Oroville only demonstrates a problem with ALL dams worldwide.
Spillways and emergency relief channels are designed to handle the biggest event the designers can imagine. By their very nature they cannot be tested to maximum design stress. There are literally a couple thousand spillways and emergency relief channels that have never carried overflow water. Every one of them is an 'untested' design. Each of them might suffer similar failures.
rfields5421 wrote:
Read up on when the overflow spillways were used at Boulder / Hoover Dam. That dam always carries a risk of overtopping. A sufficient flood could do that if it put enough water into Lake Mead. An overtopped dam will fail catastrophically if the flow is not stopped quickly.
rfields5421 wrote:What is not subject to debate is that without this dam, the city of Oroville would have been destroyed by the flooding which filled the lake to near capacity.
rfields5421 wrote:The main water discharge system failed and the backup failed; we were within a whisker of a major disaster (if you don't count the evacuation of 188,000 people a major disaster); at the current time we are far from out of danger. The snow hasn't begun to melt yet.No, I do not think this an engineering failure. The systems worked as planned/ designed.
rfields5421 wrote:Even if the emergency spillway had "lost crest control" it would have done its designed job. It is not designed to prevent all damage to the mountainside nor to the downstream area. It is an EMERGENCY spillway to only be used in an emergency to protect the main dam from damage.
rfields5421 wrote:There was obviously other water traveling down the embankment, and that non-spillway contained water could be the source of the initial failure.
rfields5421 wrote:I notice that you put emergency in quotes which indicates that you don't quite understand what happened at Orville. "loss of crest control" could have flooded a half a million homes and businesses. And we were very close to "loss of crest control".Despite the 'emergency' the main point is the system functioned mostly correctly. A completely uncontrolled flood was averted.
Tugger wrote:There is definitely re-bar in the spillway structure:
https://wattsupwiththat.files.wordpress ... hicoer.jpg
salttee wrote:I don't see any sign of rebar, that looks like a design problem to me; if there were rebar it would have been evident in the picture I posted. If the concrete for the spillway had been poured with rebar in it, it wouldn't have failed. But if not a design fault, it was an infrastructure problem anyway. I can't understand how someone could say it was neither..
salttee wrote:What I see is trace amounts of undersized rebar in the floor of the spillway. There are evidences of the anchor points into the underlying rock and it seems that the sidewalls and their foundation had appropriate amounts of reinforcement, they held up so far.
WIederling wrote:rfields5421 wrote:The current issues with Oroville only demonstrates a problem with ALL dams worldwide.
Spillways and emergency relief channels are designed to handle the biggest event the designers can imagine. By their very nature they cannot be tested to maximum design stress. There are literally a couple thousand spillways and emergency relief channels that have never carried overflow water. Every one of them is an 'untested' design. Each of them might suffer similar failures.
Baloney and neocon hogwash.
What you see is caused by pronounced maintainance shortcomings. Sorry, no money. we need the cash for profits.
https://en.wikipedia.org/wiki/Oroville_ ... nspections
https://en.wikipedia.org/wiki/2017_Oroville_Dam_crisis
Nothing unexpected or "fought valiantly and lost" about it.
mham001 wrote:It had wire mesh.
mham001 wrote:Some practices used today do not require anything on a flat surface.
salttee wrote:mham001 wrote:It had wire mesh.
That's a chain link fence you're seeing..
wingman wrote:It pains me somewhat to say it but Trump is right about our infrastructure problem.
Aesma wrote:From what I'm used to see and a bit of research, most French dams have spillways that are part of the dam structure itself. I would expect those to not be a flimsy concrete slab (or here non continuous slabs it seems) but a structure that couldn't fail in the way this one is.
What is the reason to not go that route ?
rfields5421 wrote:I can't find an exact answer, but the Oroville Spillway has carried large volumes of water many times. I can find about a dozen photos on the web from different years with water on the spillway.
The Popular Science website has a very impressive photo from 1972 of the water hitting the bottom of the spillway.
The spillway has definitely carried a lot of water safely in the past.
As I mentioned above - there was a repair done to some cracks in the spillway a few years ago. I don't think California has had enough rain/ snowmelt since those repairs to put much, if any, water down the spillway.
rfields5421 wrote:Are the French dams concrete or earthen? Many high dams such as this one are not built from solid concrete. There is a tremendous issue with cooling the concrete in a massive dam. It can be done, but is expensive and takes a lot of time.
casinterest wrote:rfields5421 wrote:I can't find an exact answer, but the Oroville Spillway has carried large volumes of water many times. I can find about a dozen photos on the web from different years with water on the spillway.
The Popular Science website has a very impressive photo from 1972 of the water hitting the bottom of the spillway.
The spillway has definitely carried a lot of water safely in the past.
As I mentioned above - there was a repair done to some cracks in the spillway a few years ago. I don't think California has had enough rain/ snowmelt since those repairs to put much, if any, water down the spillway.
Google shows the Spillway in operation from over a year ago.
https://www.google.com/maps/place/Orovi ... 121.556359
WIederling wrote:the mandatory evacuation has been mooted:
http://www.accuweather.com/en/weather-n ... m/70000833
impressive images from the defect.
salttee wrote:WIederling wrote:the mandatory evacuation has been mooted:
http://www.accuweather.com/en/weather-n ... m/70000833
impressive images from the defect.
The story you linked to is old news, but the picture is startling. It looks like the spillway has suffered a collapse of its left sidewall.
casinterest wrote:The sidewall is intact. The water went under the wall.
WIederling wrote:the mandatory evacuation has been mooted:
http://www.accuweather.com/en/weather-n ... m/70000833
impressive images from the defect.