The amount of water that is flowing would quickly erode the ground on which the spillway is built making the hole bigger and the release of the water even more uncontrollable than it already is. The Emergency Overflow has basically the same problem, with the amount of water flowing out eroding the ground quickly enough to cause the structure to become unstable.
I'm also going to be worried about the general stability of the dam itself because at the moment everything surrounding the dam seems to have a problem or two and generally these sorts of problems don't just spring up out of nowhere. If everything really -does- go tits up and the auxiliary spillway fails there's no telling what -that- does to the structure of the main dam itself.
It's almost like upfront infrastructure maintenance spending saves money by preventing the likelihood of catastrophes like an overflowing dam wiping out a dense residential town and causing hundreds of millions in damage and lost property on top of astronomical repair costs
Anyway I heard on NPR that environmental groups had raised concerns about the emergency spillway in 2005. I assume it is routine to ignore environmental groups, but did they actually identify the problem and in the intervening 12 years was any effort made at all to even bother checking it now out? What authority is in charge of maintaining/repairing this kind of infrastructure?
Let's be fair here. California had a massive massive sustained drought of extreme proportions followed by a deluge of rain. There are a bunch of things that can go wrong with that sort of set up, not the least suddenly unexpected sinkholes opening up in areas that really really don't need a sink hole.
I'm not going to blame anyone for not doing their job when this is the sort of problem that no one could have seen coming without 20/20 vision into the future.
Three environmental groups — the Friends of the River, the Sierra Club and the South Yuba Citizens League — filed a motion with the federal government on Oct. 17, 2005, as part of Oroville Dam’s relicensing process, urging federal officials to require that the dam’s emergency spillway be armored with concrete, rather than remain as an earthen hillside.
The groups filed the motion with FERC, the Federal Energy Regulatory Commission. They said that the dam, built and owned by the state of California, and finished in 1968, did not meet modern safety standards because in the event of extreme rain and flooding, fast-rising water would overwhelm the main concrete spillway, then flow down the emergency spillway, and that could cause heavy erosion that would create flooding for communities downstream, but also could cause a failure, known as “loss of crest control.”
from this article. Dunno enough about the subject to say if this is a damning indictment or if it was a reasonable error on the government's part.
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MayabirdPecking at the keyboardRegistered Userregular
Just for larger scope when is the last time a large damn failed in America? This seems like something we as a nation should be completely ashamed of.
It wasn't super-large but the Delhi Dam in northeast Iowa (pronounced Dell-high because Iowa) failed in 2010. No one died but it caused millions of dollars in flood damage to towns downstream.
Three environmental groups — the Friends of the River, the Sierra Club and the South Yuba Citizens League — filed a motion with the federal government on Oct. 17, 2005, as part of Oroville Dam’s relicensing process, urging federal officials to require that the dam’s emergency spillway be armored with concrete, rather than remain as an earthen hillside.
The groups filed the motion with FERC, the Federal Energy Regulatory Commission. They said that the dam, built and owned by the state of California, and finished in 1968, did not meet modern safety standards because in the event of extreme rain and flooding, fast-rising water would overwhelm the main concrete spillway, then flow down the emergency spillway, and that could cause heavy erosion that would create flooding for communities downstream, but also could cause a failure, known as “loss of crest control.”
from this article. Dunno enough about the subject to say if this is a damning indictment or if it was a reasonable error on the government's part.
This is the equivalent structure on a large lake near me.
Dam and spillway at top right, large, concrete emergency spillway (which was used successfully last year) at bot left.
As an aside, I'm very much not an expert and not an engineer, but I find this stuff fascinating. I think I just like water.
Current worst case scenario is that the main spillway deteriorates to an unusable state, forcing use of the emergency overflow which is uncontrolled and untested.
This weekend that occurred and alarming erosion of that structure was observed, suggesting that the aux spillway could fail. That structure has a height of 30ft (assuming it just vanished). More likely some cross section fails and uncontrolled releases in the millions of cfs occur. Levees downstream probably would not be able to cope with that release.
Which is very bad, but not the nightmare of the main dam failing.
The spillways have heights of somewhere in the range of 770 feet. They have to by mathematical necessity because they must connect the overflow point (somewhere around the top of the dam) to the outflow river (at the bottom). (Unless the outflow river flows about 740 feet up hill)
The immediate portion of the spillway at the top is only 30 feet. But if that goes the same process that caused it to fail is now acting on the immediate portion below it; except uncontrolled and with millions of gallons of water running over it at high speed.
To wit; the spillway doesn't just "become unusable" it becomes unusable because the hill on which it resides begins to fail from the water flow.
The concrete berm at the top of the emergency spillway has a height of 30ft. Below that is ... something. Strange as it may seem, it doesn't appear to be known how or if the berm structure is well anchored to the rock (hopefully bedrock) below.
They're not going to be able to access or repair the main spillway for some time, they're planning to run it constantly at high CFS for the next several months to open capacity for additional storms. And that's before spring runoff arrives, which will provide consistently high inflow for the few months after that (especially this year). I suspect the repair costs are closer to billion at this point, as they'll likely have to rebuild the spillway from scratch.
"Spillway parking," as a general idea, seems like a Bad Idea.
So, with regards to infrastructure - and I think we're all on the same page here - the costs and time involved are quite more involved than I think most people realize. I know there was some large scale bridge inspections/repairs that began about 8-10 years ago after we had that rash of bridge failures. I don't think those have all completed yet.
Also, for some perspective, the Chesapeake Bay Bridge-Tunnel has two spans next to each other; and is 17.6 miles long.
It is mandatory that the bridge be checked and serviced every five years. Since servicing the bridge takes about five years, the work never stops.
Tolls for either direction on the CBBT are on the order of $13 for a normal car. I know they are higher for tractor trailers but I'm not sure how much higher. The funds are kept separate from the state's general transportation funds; which are already below what they should be to accommodate the amount of vehicle traffic in the area.
I'm guessing that the recent drought effects put all dam work on a relatively low priority. In part because no one expected the torrential rains on the backside of the droughts (I know others said this). Also, considering politicians tend to be very myopic and only look 1-2 years ahead, it's not surprising that funds weren't diverted to infrastructure development.
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HonkHonk is this poster.Registered User, __BANNED USERSregular
Also, one thing which hasn't been mentioned here yet - the acting director only started 2 months ago, which throws a nice monkey wrench into everything, too.
Three environmental groups — the Friends of the River, the Sierra Club and the South Yuba Citizens League — filed a motion with the federal government on Oct. 17, 2005, as part of Oroville Dam’s relicensing process, urging federal officials to require that the dam’s emergency spillway be armored with concrete, rather than remain as an earthen hillside.
The groups filed the motion with FERC, the Federal Energy Regulatory Commission. They said that the dam, built and owned by the state of California, and finished in 1968, did not meet modern safety standards because in the event of extreme rain and flooding, fast-rising water would overwhelm the main concrete spillway, then flow down the emergency spillway, and that could cause heavy erosion that would create flooding for communities downstream, but also could cause a failure, known as “loss of crest control.”
from this article. Dunno enough about the subject to say if this is a damning indictment or if it was a reasonable error on the government's part.
Unfortunately a fair amount of our infrastructure is not up to current standard, but even if they pushed this report to the top of the pile, governmen being what it is it would take a while to get to, and then oops historic recession, oops historic drought, somehow spending money for heavy rain levels down the road doesn't happen.
Which isn't to say that is the correct way to handle things at all, but google lake oroville 2014 to see how low it was and imagine how well spending money to retrofit that dam spillway for heavy rain would go over.
(Would link but on mobile and don't want to drop in a massive image by accident)
Edit: changed historic rain to heavy rain, as I don't know that this is historic levels technically, but still pretty high
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AegisFear My DanceOvershot Toronto, Landed in OttawaRegistered Userregular
Also, one thing which hasn't been mentioned here yet - the acting director only started 2 months ago, which throws a nice monkey wrench into everything, too.
He's been giving some pretty nice press conferences. Here's one from the 12th (He starts talking around 6:30. I was trying to find the youtube link, but the channel was shut down, so here's the Department of Water Resource's Periscope channel, whatever Periscope is) where he starts talking about the initial issues that they encountered and gives a lot more background.
Three environmental groups — the Friends of the River, the Sierra Club and the South Yuba Citizens League — filed a motion with the federal government on Oct. 17, 2005, as part of Oroville Dam’s relicensing process, urging federal officials to require that the dam’s emergency spillway be armored with concrete, rather than remain as an earthen hillside.
The groups filed the motion with FERC, the Federal Energy Regulatory Commission. They said that the dam, built and owned by the state of California, and finished in 1968, did not meet modern safety standards because in the event of extreme rain and flooding, fast-rising water would overwhelm the main concrete spillway, then flow down the emergency spillway, and that could cause heavy erosion that would create flooding for communities downstream, but also could cause a failure, known as “loss of crest control.”
from this article. Dunno enough about the subject to say if this is a damning indictment or if it was a reasonable error on the government's part.
Unfortunately a fair amount of our infrastructure is not up to current standard, but even if they pushed this report to the top of the pile, governmen being what it is it would take a while to get to, and then oops historic recession, oops historic drought, somehow spending money for heavy rain levels down the road doesn't happen.
Which isn't to say that is the correct way to handle things at all, but google lake oroville 2014 to see how low it was and imagine how well spending money to retrofit that dam spillway for heavy rain would go over.
(Would link but on mobile and don't want to drop in a massive image by accident)
Edit: changed historic rain to heavy rain, as I don't know that this is historic levels technically, but still pretty high
Theoretically this is exactly what the rainy day fund Jerry Brown got us doing is for, but this thing almost certainly falls under federal jurisdiction right?
If I'm not mistaken (and most of this is from reading other forums on this thing), Oroville Dam is state jurisdiction, not federal (it's managed by the state, not by federal employees), but there's a shared jurisdiction over some aspect - might have to do with the electricity generation. I can't quite remember what. The gist I understood is that it's basically a shared state/fed thing, but mostly (like 80+%) state.
If I'm not mistaken (and most of this is from reading other forums on this thing), Oroville Dam is state jurisdiction, not federal (it's managed by the state, not by federal employees), but there's a shared jurisdiction over some aspect - might have to do with the electricity generation. I can't quite remember what. The gist I understood is that it's basically a shared state/fed thing, but mostly (like 80+%) state.
Oroville is a state dam.
Basically there were two massive water projects in the state, the Central Valley Project (federal) and the State Water Project (state). This doesn't include other projects, like hetch hetchy, owens valley, etc, that were built by individual cities (san Francisco and Los Angeles respectively in this case)
In the end they all dump into the same place eventually, but until then you get a mess of jurisdictions. For example, federal dams include Folsom on the American river and shasta way up on the sacramento river. Oroville is a state dam on the feather river. Well the feather eventually joins the sacramento river north of the City of Sacramento, and the American hits the Sacramento river in the middle of Sacramento. So even though the state owns oroville they still have to work with the feds on shasta, Folsom (and wherever else) so that they don't all dump a ton of water into the city at one. Like, say, when shasta is full, Oroville is full and broken, and Folsom is dumping water for flood control purposes. While there are already broken levees downstream from the unrestricted cosumnes river.
You know, hypothetically
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MrMisterJesus dying on the cross in pain? Morally better than us. One has to go "all in".Registered Userregular
Also, I feel compelled to mention that dam failures are actually one of the few points in life where "acre-feet" is a really sensible unit
I think you guys are missing the true opportunity here. They just need to build a ramp and jump the water over the hole. That would be so rad. Extra points for getting the water to do flips mid-air before landing in the rest of the spillway.
Current worst case scenario is that the main spillway deteriorates to an unusable state, forcing use of the emergency overflow which is uncontrolled and untested.
This weekend that occurred and alarming erosion of that structure was observed, suggesting that the aux spillway could fail. That structure has a height of 30ft (assuming it just vanished). More likely some cross section fails and uncontrolled releases in the millions of cfs occur. Levees downstream probably would not be able to cope with that release.
Which is very bad, but not the nightmare of the main dam failing.
The spillways have heights of somewhere in the range of 770 feet. They have to by mathematical necessity because they must connect the overflow point (somewhere around the top of the dam) to the outflow river (at the bottom). (Unless the outflow river flows about 740 feet up hill)
The immediate portion of the spillway at the top is only 30 feet. But if that goes the same process that caused it to fail is now acting on the immediate portion below it; except uncontrolled and with millions of gallons of water running over it at high speed.
To wit; the spillway doesn't just "become unusable" it becomes unusable because the hill on which it resides begins to fail from the water flow.
The concrete berm at the top of the emergency spillway has a height of 30ft. Below that is ... something. Strange as it may seem, it doesn't appear to be known how or if the berm structure is well anchored to the rock (hopefully bedrock) below.
They're not going to be able to access or repair the main spillway for some time, they're planning to run it constantly at high CFS for the next several months to open capacity for additional storms. And that's before spring runoff arrives, which will provide consistently high inflow for the few months after that (especially this year). I suspect the repair costs are closer to billion at this point, as they'll likely have to rebuild the spillway from scratch.
Below that is dirt for 740 feet. You can see it in the picture from above. Just as the water is carving an increasingly large section of the land around the spillway out the section where they did the emergency release was shedding land as it was released (the area clear of grass and trees just below the emergency spillway berm).
The question is, mainly, which area do they think is more stable/less likely to fail. At the moment they think that is the land under the spillway. And let's hope they're right.
Current worst case scenario is that the main spillway deteriorates to an unusable state, forcing use of the emergency overflow which is uncontrolled and untested.
This weekend that occurred and alarming erosion of that structure was observed, suggesting that the aux spillway could fail. That structure has a height of 30ft (assuming it just vanished). More likely some cross section fails and uncontrolled releases in the millions of cfs occur. Levees downstream probably would not be able to cope with that release.
Which is very bad, but not the nightmare of the main dam failing.
The spillways have heights of somewhere in the range of 770 feet. They have to by mathematical necessity because they must connect the overflow point (somewhere around the top of the dam) to the outflow river (at the bottom). (Unless the outflow river flows about 740 feet up hill)
The immediate portion of the spillway at the top is only 30 feet. But if that goes the same process that caused it to fail is now acting on the immediate portion below it; except uncontrolled and with millions of gallons of water running over it at high speed.
To wit; the spillway doesn't just "become unusable" it becomes unusable because the hill on which it resides begins to fail from the water flow.
The concrete berm at the top of the emergency spillway has a height of 30ft. Below that is ... something. Strange as it may seem, it doesn't appear to be known how or if the berm structure is well anchored to the rock (hopefully bedrock) below.
They're not going to be able to access or repair the main spillway for some time, they're planning to run it constantly at high CFS for the next several months to open capacity for additional storms. And that's before spring runoff arrives, which will provide consistently high inflow for the few months after that (especially this year). I suspect the repair costs are closer to billion at this point, as they'll likely have to rebuild the spillway from scratch.
Below that is dirt for 740 feet. You can see it in the picture from above. Just as the water is carving an increasingly large section of the land around the spillway out the section where they did the emergency release was shedding land as it was released (the area clear of grass and trees just below the emergency spillway berm).
The question is, mainly, which area do they think is more stable/less likely to fail. At the moment they think that is the land under the spillway. And let's hope they're right.
Nah. It's dirt and fill at least partway down, but there's rock underneath.
Not that this is a major update place or anything, but the evacuation has been reduced to an evac warning - people can return home. Likely to get everything in order for when they've got to get out this weekend.
Well, that's bad. I guess we're going to find out how much bedrock is down there once and for all, because they're going to have to run the main spillway incredibly hard to avoid overflowing the emergency with that much water coming in.
Took a bit to get there, but federal funding approved.
Interesting- according to that article, the recommendation back in 2005 wasn't that the spillway (that has a big chunk out of it now) was structurally unsound, but that the hill underneath the emergency spillway (long 30-ft wall) should be "armored" with concrete or boulders to prevent erosion. Also the state water resources officials lied about the 2005 review multiple times in official paperwork, saying that there were "no significant concerns" about the emergency spillway.
The official license for the dam expired in 2007 but for some reason it has been automatically renewed each year since (under a "temporary" license), and only last year after almost a decade did they find the necessary documents to start the approval process. This is looking more and more like crass incompetence at the state level.
The President's approved aid for communities and repair of the eroded hillside using FEMA, but can he approve money for "upgrading" the dam by armoring the hillside? Or does that fall under something Congress would have to vote on first?
Took a bit to get there, but federal funding approved.
Interesting- according to that article, the recommendation back in 2005 wasn't that the spillway (that has a big chunk out of it now) was structurally unsound, but that the hill underneath the emergency spillway (long 30-ft wall) should be "armored" with concrete or boulders to prevent erosion. Also the state water resources officials lied about the 2005 review multiple times in official paperwork, saying that there were "no significant concerns" about the emergency spillway.
The official license for the dam expired in 2007 but for some reason it has been automatically renewed each year since (under a "temporary" license), and only last year after almost a decade did they find the necessary documents to start the approval process. This is looking more and more like crass incompetence at the state level.
The President's approved aid for communities and repair of the eroded hillside using FEMA, but can he approve money for "upgrading" the dam by armoring the hillside? Or does that fall under something Congress would have to vote on first?
honestly, the reason they never did anything to the hillside is because they probably never expected anything like this. rarely ever are things designed for the absolute worst case scenario because they would cost infinite amounts of money. and it's really hard to rationalize spending billions of dollars to upgrade the overflow structures of an empty lake in a drought. the engineers had no significant concerns. some environmental groups did but having not seen the reports it's easy to say "well look at what is happening now obviously they should have done something" but that is not how any sort of reasonable engineering or conversation about engineering happens.
no upgrades or repairs really matter for the immediate emergency, because they can't stop running the main spillway at 100,000 cfs to do anything about it.
That's the shitty aspect of it of course, had the state said "we're going to spend millions of dollars to upgrade an emergency spillway that's never been used -EVER" in the middle of a drought people would lose their shit about government waste. So they don't, finally need to use it, and now it's "ermg why didn't you upgrade this?"
Seriously though, the main push from DWR the past few years has been trying to find a way to send more water down to southern california. Literally only a few months ago everything was about the drought, conservation, meters, etc. Unfortunately this sort of thing only gets attention after a crisis, until then it's just on a list of "things to be done when we have unlimited time and money"
"Spillway parking," as a general idea, seems like a Bad Idea.
Because of oil and such? I assume there's time to move cars in most situations where a spill way would be needed
It's pretty common as I know at least where I am, the area below the spillway is a park when it's not locked off. It's a good use of otherwise dead land. Lots of dog walking etc.
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Let's be fair here. California had a massive massive sustained drought of extreme proportions followed by a deluge of rain. There are a bunch of things that can go wrong with that sort of set up, not the least suddenly unexpected sinkholes opening up in areas that really really don't need a sink hole.
I'm not going to blame anyone for not doing their job when this is the sort of problem that no one could have seen coming without 20/20 vision into the future.
from this article. Dunno enough about the subject to say if this is a damning indictment or if it was a reasonable error on the government's part.
It wasn't super-large but the Delhi Dam in northeast Iowa (pronounced Dell-high because Iowa) failed in 2010. No one died but it caused millions of dollars in flood damage to towns downstream.
This is the equivalent structure on a large lake near me.
Dam and spillway at top right, large, concrete emergency spillway (which was used successfully last year) at bot left.
As an aside, I'm very much not an expert and not an engineer, but I find this stuff fascinating. I think I just like water.
The concrete berm at the top of the emergency spillway has a height of 30ft. Below that is ... something. Strange as it may seem, it doesn't appear to be known how or if the berm structure is well anchored to the rock (hopefully bedrock) below.
They're not going to be able to access or repair the main spillway for some time, they're planning to run it constantly at high CFS for the next several months to open capacity for additional storms. And that's before spring runoff arrives, which will provide consistently high inflow for the few months after that (especially this year). I suspect the repair costs are closer to billion at this point, as they'll likely have to rebuild the spillway from scratch.
So, with regards to infrastructure - and I think we're all on the same page here - the costs and time involved are quite more involved than I think most people realize. I know there was some large scale bridge inspections/repairs that began about 8-10 years ago after we had that rash of bridge failures. I don't think those have all completed yet.
Also, for some perspective, the Chesapeake Bay Bridge-Tunnel has two spans next to each other; and is 17.6 miles long. Tolls for either direction on the CBBT are on the order of $13 for a normal car. I know they are higher for tractor trailers but I'm not sure how much higher. The funds are kept separate from the state's general transportation funds; which are already below what they should be to accommodate the amount of vehicle traffic in the area.
I'm guessing that the recent drought effects put all dam work on a relatively low priority. In part because no one expected the torrential rains on the backside of the droughts (I know others said this). Also, considering politicians tend to be very myopic and only look 1-2 years ahead, it's not surprising that funds weren't diverted to infrastructure development.
That's the weirdest thing I've seen in a while.
Also, one thing which hasn't been mentioned here yet - the acting director only started 2 months ago, which throws a nice monkey wrench into everything, too.
Going from super-dry to over-the-top in less than two months, and it doesn't curve; it spikes.
Unfortunately a fair amount of our infrastructure is not up to current standard, but even if they pushed this report to the top of the pile, governmen being what it is it would take a while to get to, and then oops historic recession, oops historic drought, somehow spending money for heavy rain levels down the road doesn't happen.
Which isn't to say that is the correct way to handle things at all, but google lake oroville 2014 to see how low it was and imagine how well spending money to retrofit that dam spillway for heavy rain would go over.
(Would link but on mobile and don't want to drop in a massive image by accident)
Edit: changed historic rain to heavy rain, as I don't know that this is historic levels technically, but still pretty high
He's been giving some pretty nice press conferences. Here's one from the 12th (He starts talking around 6:30. I was trying to find the youtube link, but the channel was shut down, so here's the Department of Water Resource's Periscope channel, whatever Periscope is) where he starts talking about the initial issues that they encountered and gives a lot more background.
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Theoretically this is exactly what the rainy day fund Jerry Brown got us doing is for, but this thing almost certainly falls under federal jurisdiction right?
Also, Periscope is basically Facebook Live before Facebook Live.
Brunnel
You want a fun graph, look at Folsom Lake
Its primary purpose is flood control, so it has to keep releasing in order to be prepared for the next storm.
Oroville is a state dam.
Basically there were two massive water projects in the state, the Central Valley Project (federal) and the State Water Project (state). This doesn't include other projects, like hetch hetchy, owens valley, etc, that were built by individual cities (san Francisco and Los Angeles respectively in this case)
In the end they all dump into the same place eventually, but until then you get a mess of jurisdictions. For example, federal dams include Folsom on the American river and shasta way up on the sacramento river. Oroville is a state dam on the feather river. Well the feather eventually joins the sacramento river north of the City of Sacramento, and the American hits the Sacramento river in the middle of Sacramento. So even though the state owns oroville they still have to work with the feds on shasta, Folsom (and wherever else) so that they don't all dump a ton of water into the city at one. Like, say, when shasta is full, Oroville is full and broken, and Folsom is dumping water for flood control purposes. While there are already broken levees downstream from the unrestricted cosumnes river.
You know, hypothetically
Imperial 4 lyfe
It might hypothetically be possible, but it's hard to overstate this rate of flow.
When someone talks CFS, just as a ballpark, imagine a basketball going by in a second.
We're talking a rate of 100,000 CFS. So in a given second, past a point, 100,000 basketballs are going by.
There's enough water going down that it's going into the hole and enough water is shooting back up to completely cover the rest of the spillway down.
Below that is dirt for 740 feet. You can see it in the picture from above. Just as the water is carving an increasingly large section of the land around the spillway out the section where they did the emergency release was shedding land as it was released (the area clear of grass and trees just below the emergency spillway berm).
The question is, mainly, which area do they think is more stable/less likely to fail. At the moment they think that is the land under the spillway. And let's hope they're right.
Nah. It's dirt and fill at least partway down, but there's rock underneath.
Cubic meters are still better and cubic kilometers have a better sense of scale in an actual failure scenario
See that yellow? See that little blob to the left side of it? That's Lake Oroville.
http://sanfrancisco.cbslocal.com/2017/02/14/president-trump-monitoring-oroville-dam-evacuations/
Took a bit to get there, but federal funding approved.
e: Worth noting these are not forecasts, they're model projections. Not quite the same thing.
http://cdec.water.ca.gov/river/res_ORO.html for those who want to follow at home.
The official license for the dam expired in 2007 but for some reason it has been automatically renewed each year since (under a "temporary" license), and only last year after almost a decade did they find the necessary documents to start the approval process. This is looking more and more like crass incompetence at the state level.
The President's approved aid for communities and repair of the eroded hillside using FEMA, but can he approve money for "upgrading" the dam by armoring the hillside? Or does that fall under something Congress would have to vote on first?
honestly, the reason they never did anything to the hillside is because they probably never expected anything like this. rarely ever are things designed for the absolute worst case scenario because they would cost infinite amounts of money. and it's really hard to rationalize spending billions of dollars to upgrade the overflow structures of an empty lake in a drought. the engineers had no significant concerns. some environmental groups did but having not seen the reports it's easy to say "well look at what is happening now obviously they should have done something" but that is not how any sort of reasonable engineering or conversation about engineering happens.
no upgrades or repairs really matter for the immediate emergency, because they can't stop running the main spillway at 100,000 cfs to do anything about it.
Because of oil and such? I assume there's time to move cars in most situations where a spill way would be needed
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It's pretty common as I know at least where I am, the area below the spillway is a park when it's not locked off. It's a good use of otherwise dead land. Lots of dog walking etc.