California Drought

[turnkey4099]

As a retired engineer my heart goes out to the people working to reason their way toward a solution. They are dealing with 40+ year old infrastructure and most of the people that designed and built it are no longer available to lend their experience and guidance to the effort. They're also up against Mother Nature and have no control over the path she takes. If these challenges weren't enough, the attitudes held by much of the press and the public are especially unfriendly to technology, especially that which impacts the environment. The biggest contribution this forum can make is to facilitate the dissemination of factual information related to the spillway failure to counter the fear mongering that's already going on and the witch hunts that will surely follow.

Very cogent and true.

 

[tcreeley]

Too much water for the capacity
: Oroville, California - breaching spillways and evacuations.

 

[dickfoster]

You have to wonder if the higher ups might be holding back information to keep a full out pandemic situation from occuring. Thus, a smooth exodus.

Here on the gulf coast, they "over hype" hurricanes to get people to leave early.

I think they are. That big hole in the main spillway is a really bad deal on what is really just a big pile of clay soil. If you know how clay dams have to work then you know it's a serious deal.
The reason the spillway gave way is because the clay core essentially dried out and shrank over the course of the recent drought. From the footage I've seen, the spillway was built with unreinforced concrete. When the earth dried out what you had was a crust of unreinforced concrete which simply caved in when they starting putting a lot of heavy water over it.
Now you have the opposite problem where they are now pouring water into the clay core though that spillway failure which has the effect of simply dissolving the core and making failure of the entire dam a real possibility. Imagine making up a ball of clay and dropping into a bucket of water.
Now you're talking about a 900' deep lake being cut loose to run down the Feather River and flooding out everything down to and including Sacramento. The entire Sacramento valley area down to Stockton and beyond has many many levies that aren't in the best of shape. They have been fretting about for those for some years already. Some of these levies are starting to show their age and are being a problem with the recent water deluge. Now add all of that water from lake Oroville on top of that and you've got yourself some real problems. I'm not trying to be a fear monger just tell it the way it is. I think they are running on luck more than anything else right now. With a bit more luck they will make it through the spring runoff when that record snowpack melts when they will be about to effect some real repairs to that spillway. That would be to skin the entire main spillway with reinforced concrete and to also skin the emergency spillway to prevent erosion of the dam below it should it ever need to be used again.

 

[hawkeye08]

I think they are. That big hole in the main spillway is a really bad deal on what is really just a big pile of clay soil. If you know how clay dams have to work then you know it's a serious deal.
The reason the spillway gave way is because the clay core essentially dried out and shrank over the course of the recent drought. From the footage I've seen, the spillway was built with unreinforced concrete. When the earth dried out what you had was a crust of unreinforced concrete which simply caved in when they starting putting a lot of heavy water over it.
Now you have the opposite problem where they are now pouring water into the clay core though that spillway failure which has the effect of simply dissolving the core and making failure of the entire dam a real possibility. Imagine making up a ball of clay and dropping into a bucket of water.
Now you're talking about a 900' deep lake being cut loose to run down the Feather River and flooding out everything down to and including Sacramento. The entire Sacramento valley area down to Stockton and beyond has many many levies that aren't in the best of shape. They have been fretting about for those for some years already. Some of these levies are starting to show their age and are being a problem with the recent water deluge. Now add all of that water from lake Oroville on top of that and you've got yourself some real problems. I'm not trying to be a fear monger just tell it the way it is. I think they are running on luck more than anything else right now. With a bit more luck they will make it through the spring runoff when that record snowpack melts when they will be about to effect some real repairs to that spillway. That would be to skin the entire main spillway with reinforced concrete and to also skin the emergency spillway to prevent erosion of the dam below it should it ever need to be used again.

Not sure what you mean by unreinforced concrete, but looking at the photos on the other website, there is a bunch of rebar in it... are you referring to something other??

 

[Egon]

Lots of pictures with reinforcing showing.

 

[houstonscott]

Oroville Dam: Feds and state officials ignored warnings 12 years ago

They knew.

 

[dickfoster]

Not sure what you mean by unreinforced concrete, but looking at the photos on the other website, there is a bunch of rebar in it... are you referring to something other??

I couldn't see rebar in the footage I saw. Maybe in the sides but not the bottom If it was there then good so I guess it wasn't thick enough to take the weight unsupported by the subsoil. Whatever, it's a serious problem now.

 

[aczlan]

I think they are. That big hole in the main spillway is a really bad deal on what is really just a big pile of clay soil. If you know how clay dams have to work then you know it's a serious deal.
The reason the spillway gave way is because the clay core essentially dried out and shrank over the course of the recent drought. From the footage I've seen, the spillway was built with unreinforced concrete. When the earth dried out what you had was a crust of unreinforced concrete which simply caved in when they starting putting a lot of heavy water over it.
Now you have the opposite problem where they are now pouring water into the clay core though that spillway failure which has the effect of simply dissolving the core and making failure of the entire dam a real possibility. Imagine making up a ball of clay and dropping into a bucket of water.
Now you're talking about a 900' deep lake being cut loose to run down the Feather River and flooding out everything down to and including Sacramento. The entire Sacramento valley area down to Stockton and beyond has many many levies that aren't in the best of shape. They have been fretting about for those for some years already. Some of these levies are starting to show their age and are being a problem with the recent water deluge. Now add all of that water from lake Oroville on top of that and you've got yourself some real problems. I'm not trying to be a fear monger just tell it the way it is. I think they are running on luck more than anything else right now. With a bit more luck they will make it through the spring runoff when that record snowpack melts when they will be about to effect some real repairs to that spillway. That would be to skin the entire main spillway with reinforced concrete and to also skin the emergency spillway to prevent erosion of the dam below it should it ever need to be used again.

Please, before fearmongering, read this whole thread (I posted several pictures showing the concrete with rebar in it), then look at the linked thread at Metabunk (Oroville Dam Spillway Failure | Metabunk).
The upper part of the spillway is carved into a rock outcropping, the spillway and emergency spillway are built on top of a rock outcropping.
Worst case, they lose the emergency spillway and 30 feet of the lake dumps downstream. While that would be a big problem, the rest of the dam is not going anywhere.
Let me repost a picture showing where things sit:

Picture of the whole area with some good markings of where everything is to give some perspective:
View attachment 498656
Source: Twitter

Even if both spillways blow out, there is still a large shoulder with rock underneath that it has to get around before it can eat into the dam itself.
In this picture, you can see the rock lining the side of the main spillway:

Source: Oroville Dam Spillway Failure | Page 7 | Metabunk
The evacuation was in case the emergency spillway blew out as they were getting undercutting that was getting close to the base of the emergency spillway.

Aaron Z

 

[dickfoster]

Please, before fearmongering, read this whole thread (I posted several pictures showing the concrete with rebar in it), then look at the linked thread at Metabunk (Oroville Dam Spillway Failure | Metabunk).
The upper part of the spillway is carved into a rock outcropping, the spillway and emergency spillway are built on top of a rock outcropping.
Worst case, they lose the emergency spillway and 30 feet of the lake dumps downstream. While that would be a big problem, the rest of the dam is not going anywhere.
Let me repost a picture showing where things sit:

Even if both spillways blow out, there is still a large shoulder with rock underneath that it has to get around before it can eat into the dam itself.
In this picture, you can see the rock lining the side of the main spillway:
View attachment 498668
Source: Oroville Dam Spillway Failure | Page 7 | Metabunk
The evacuation was in case the emergency spillway blew out as they were getting undercutting that was getting close to the base of the emergency spillway.

Aaron Z

You can stand down there if feel safe but I'll stay up here on the hill high above it all.
I know how earthen works dams are supposed to work and what too much water does to clay. It's clay and not rocks that is supposed to hold the water back. Rocks are permeable unless it's solid rock and it's clay that makes earthwork dams hold water. All that red stuff you're seeing is clay. The rock rubble or rip-rap is just there to protect the earthen structure from physical wave action. In the end, only time will tell.

Here is a cross section of the Oroville Dam which is one of the highest embankment dams in the world. Until 1980 or so it was the highest in the world. The so called impervious core bit that is supposed to hold the water back is simply compacted clay.

 

[aczlan]

You can stand down there if feel safe but I'll stay up here on the hill high above it all.
I know how earthen works dams are supposed to work and what too much water does to clay. It's clay and not rocks that is supposed to hold the water back. Rocks are permeable unless it's solid rock and it's clay that makes earthwork dams hold water. All that red stuff you're seeing is clay. The rock rubble or rip-rap is just there to protect the earthen structure from physical wave action. In the end, only time will tell.
View attachment 498670
Here is a cross section of the Oroville Dam which is one of the highest embankment dams in the world. Until 1980 or so it was the highest in the world. The so called impervious core bit that is supposed to hold the water back is simply compacted clay.

The spillway is NEXT to the dam, NOT ON the dam. The area that the spillways are in is a shoulder of rock. That is why they built it there
If you look at the main spillway, it has scoured out the clay and the reclaimed tailings that they used for fill and the area is down to rock (other than the corners of the bottom end of the upper spillway which are still eroding uphill a little), this can be seen by comparing the reddish flume coming off the main spillway for the first day or two to the white flume coming off now.
See Oroville Dam Spillway Failure | Page 3 | Metabunk for comparison pictures.
The emergency spillway is 20 feet lower than the top of the actual dam, it is not likely that there will be enough water to fill the lake to where it over tops the emergency spillway by 20 feet.

Aaron Z