California Drought

[k0ua]

Didn't you know: "All the gold in California / Is in the bank in the middle of Beverly Hills / In somebody else's name. "

Just kidding, I am sure there is plenty of good color left to find

 

[turnkey4099]

So.... I'm just sitting here reading all this and wondering what the issue was with using the emergency spillway. So here are some facts, the dam is an earthen dam, I.e. Dirt and rock filled, not solid concrete. The emergency spillway is built right on top of this earthen structure, by the same outfit that built the spillway on top of a rock base. I did a search to see about the geology of the ground the dam was built on and really found nothing. Many people are using the term bedrock. I think that is an assumption that may not be correct. In mountainous areas the term granite is used as the bedrock is usually thrust up. I don't see much granite around. I see a lot of dirt.

Now I understand why they don't want to use the emergency spillway.

If it's anything like the ones in Texas, there is no "choice" involved. When the dam pool reaches a certain level, it runs over. The only control is how much water they can run through the normal operations to keep the pool below spill over and the inflow has exceeded the outflow capabliltiy of that.

 

[RedNeckGeek]

No limestone.

Take a look at the photo above. It comes from the Metabunk web site, about half way down the cited page. It shows the bottom of the hole in the spillway after the first time DWR stopped the water flow. The stone is gray, not green, like the serpentine in this area. To me, that makes it limestone. I say this for a few reasons:

I live on the bank of the West Branch of the Feather River, upstream from the dam site, and both green serpentine and limestone can be found in abundance under my property. Bands of these limestone outcroppings can be observed in the canyon wall from the bridge that crosses the West Branch a few miles closer to the dam than my home. A marina nearby is named Lime Saddle, and back in the '20s limestone was mined and converted to cement in kilns that can still be found downslope from my property. Unfortunately, my well is drilled into that limestone, and as a result the harness of the water is very high.

When the serpentine around here gets wet, it turns dark green. Since the photo was taken shortly after the water was shut off, it is reasonable to conclude that the rock shown is wet. Another photo located closer to the top of that same Metabunk page shows water dripping off the broken spillway concrete and two workers in the hole, one of them in full raingear. The rock in both photos does not show the dark green color that is characteristic of the serpentine in this area. It's gray, same as the limestone on the canyon wall when it gets wet. It's been wet a lot this winter, and I pass over that bridge and look at it every time I head into town.

Very likely there is serpentine in the area that the dam was built, but I don't see any in the photo. It's limestone.

Somewhere is a geologic survey map of the Oroville Dam area, but I've been unable to find it online. I did find one for the Auburn Dam, and areas of serpentine are clearly marked.

But what difference does it make what the rock is for the purposes of this discussion? The original concern was that the spillway was built on earth fill, which would rapidly erode back to the reservoir once the concrete broke. That is clearly not the case, so perhaps we can come to agreement over that and move on?

 

[California]

... I am sure there is plenty of good color left to find

All the easy stuff is in ingots by now. The last large scale gold mining is in central Nevada (Carlin vicinity) using huge earthmoving equipment and barely recovering more than the cost of of the earthmoving. I know of a large concrete/asphalt supplier that is likely the largest gold producer in California - but the gold is a byproduct of his refining old dredger tailings into washed sand/gravel for paving material. (article)

Gold mining is a gamble that the return exceeds the cost of operation. I joke that our hobby mining was profitable if you're talking about direct daily operating cost, ie the gas used by the 5hp floating pump, but a real cost analysis would result similar to trout fishing where each trout costs $ thousands if you include the specialized gear, the 4x4 needed to get in there, abandoned road clearing, feeding the crew (family & guests) and other related costs a commercial operation has to consider for a cost analysis. We knew an old miner up there who over a lifetime likely didn't match welfare-level income from his hard work. His regular job down in Oroville (Caterpillar operator) supported his mining hobby.

 

[California]

View attachment 498548
The original concern was that the spillway was built on earth fill, which would rapidly erode back to the reservoir once the concrete broke. That is clearly not the case, so perhaps we can come to agreement over that and move on?

Agree.

The spillway isn't on earth fill, its on rock that didn't erode when the Feather River cut down and made its canyon.

That photo looks to me like ancient laminated something, with white (quartz?) intrusion. I too looked for geology info before posting, found nothing.

 

[farmer2009]

Try this site. Web Soil Survey
Draw out an area of interest and use soil data explorer.

 

[aczlan]

Looks like the emergency spillway is eroding and could fail (causing the top 30 feet of the emergency spillway to fail). An evacuation has been ordered for areas directly downstream.

Due to the rock outcropping under the emergency spillway, this cannot cause the dam itself to fail, but dropping 30' at once will not be good.
Oroville Dam Spillway Failure | Page 4 | Metabunk

Aaron Z

 

[bcp]

Updates:

CA - DWR (@CA_DWR) on Twitter

Bruce

 

[Kyle_in_Tex]

Prayers for everyone to get out of harms way.

 

[TemporaryKubotaOwnerMark]

That photo looks to me like ancient laminated something, with white (quartz?) intrusion.

Probably. Looks like it. Can't say without putting boots on the ground.