California Drought

[California]

Metabunk seems to be collecting and posting the most up-to-the-minute updates available anywhere.

Latest now is photos of the water starting to go over the emergency spillway at 9am today.

Oroville Dam Spillway Failure | Page 2 | Metabunk

 

[RedNeckGeek]

Anyone doesn't think this is a major failure and is just a small problem, is just who you don't want to listen to.... Because it is.... A warm spring and all that snow pack coming off in a month combined with rain, and you've got a disaster, and yes with enough water undermining this the dam might not fail but the whole thing could cut a new channel around the dam, real fast.

And some people just won't be happy until there is such a catastrophe.

Though I wouldn't be endangered by such an event, it would have a dramatic impact on me and my immediate neighbors. And the death tole in Oroville and the surroundings would be huge. People here are preparing as best they can, and sure as He11 don't need a bunch of Chicken Littles adding to the confusion. Mr. Scott, if you don't have any factual information or positive ideas to contribute, I for one would appreciate it if you'd just keep your rumors and dooms day predictions to yourself.

 

[dickfoster]

And some people just won't be happy until there is such a catastrophe.

Though I wouldn't be endangered by such an event, it would have a dramatic impact on me and my immediate neighbors. And the death tole in Oroville and the surroundings would be huge. People here are preparing as best they can, and sure as He11 don't need a bunch of Chicken Littles adding to the confusion. Mr. Scott, if you don't have any factual information or positive ideas to contribute, I for one would appreciate it if you'd just keep your rumors and dooms day predictions to yourself.

You should be busy building your ark instead of wasting your time on this board. LOL
If end up not needing the ark you can always use it to store water for the next drought which will be here before ya know it.

 

[ForestGrump]

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.

 

[RedNeckGeek]

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

The main concern I've heard expressed with respect to the emergency spillway is the additional debris and mud that will be dumped into the Feather River. If you review the Metabunk links posted earlier in this thread, you'll find that both the main spillway and emergency spillway cross rock outcroppings where they meet the reservoir, and the rock extends quite a way down the hillside if not all the way to the river. Keep in mind that all of this area was laid bare to bedrock during construction of the dam. As you say, there is little to no granite in the area, it is primarily limestone and what the locals call shale, I think geologists would call it schist. It's a strong metamorphic rock formed when sedimentary layers are subjected to tremendous heat and pressure. My home is built on it, and my neighbor would be the first to tell you it's very tough to get through with a bulldozer or backhoe. The Metabank pages show outcroppings of these rock strata that underlie the main and emergency spillways, about half way down the first page. If you search for photos showing Lake Oroville during the drought summers you'll find that the canyon walls are quite steep all the way around, an indication that the river had to work very hard to cut down through those layers of rock. I have confidence that the engineers and geologists that sited the dam spent a lot of time understanding what was under it and how water flowing in all of the spillways would interact with the geology of the area. We're not talking roaring twenties engineering like that that dominated much of the dam construction in Southern California and led to some spectacular dam failures. Construction of the Oroville Dam didn't start until 1968, and planning went all the way back to the '50s.

I also think there's reluctance to be the first to use the emergency spillway, even though the engineering and construction methods seem sound. The proof is always in the pudding, and now we're getting it. Let's hope it turns out like the Y2K fiasco, another tempest in a teapot.

 

[bcp]

Water over emergency spillway photo here:

Oroville Dam emergency spillway in use for first time in history - SFGate

Bruce

 

[buckeyefarmer]

Terrible journalism. "officials at Oroville Dam took the unprecedented step of opening the lake’s emergency spillway. "

Really? How did they open it?

 

[Egon]

Limestone underlayment???

 

[California]

No limestone.

Geology there is complex. The western slope of the Sierras is a chaotic jumble resulting from two major tectonic plates pushing against each other and causing uplift. Terrain from diverse geologic eras can appear right next to each other, separated only by slip lines that can be near vertical.

I have a gold mining claim 40 miles NE of there, up a tributary perhaps 150 river miles upstream. Bedrock there is serpentine which is sedimentary layers compressed and aged into laminations that are near vertical instead of horizontal due to this uplift. Modern streams have cut down to this bedrock, and the streams carry gravel bearing gold nuggets (we still find a few, the '49ers got most of them). This gravel is the streambed residue from a far larger prehistoric river that the modern streams intersect. (And in my area a lava ash cap from Mt Lassen, similar to concrete, overlays all this). The mines in my region generally extract this ancient streambed gravel and crush it, in contrast to a hardrock mine.

The dredger tailings hauled up the Feather River Canyon to build that dam were the output from floating gold-extracting dredges that operated up until WWII in the area below the present dam, processing ancient river gravel that deposited down there where the Feather River velocity slowed.

Its complicated. Those hillsides surrounding the dam are likely hard enough to not erode, but a perhaps greater risk is an earthquake that shifts land along a fault line. Filling the reservoir led to a couple of earthquakes. Who knows what stresses are building with the reservoir now full.

 

[dragoneggs]

No limestone.

Geology there is complex. The western slope of the Sierras is a chaotic jumble resulting from two major tectonic plates pushing against each other and causing uplift. Terrain from diverse geologic eras can appear right next to each other, separated only by slip lines that can be near vertical.

I have a gold mining claim 40 miles NE of there, up a tributary perhaps 150 river miles upstream. Bedrock there is serpentine which is sedimentary layers compressed and aged into laminations that are near vertical instead of horizontal due to this uplift. Modern streams have cut down to this bedrock, and the streams carry gravel bearing gold nuggets (we still find a few, the '49ers got most of them). This gravel is the streambed residue from a far larger prehistoric river that the modern streams intersect. (And in my area a lava ash cap from Mt Lassen, similar to concrete, overlays all this). The mines in my region generally extract this ancient streambed gravel and crush it, in contrast to a hardrock mine.

The dredger tailings hauled up the Feather River Canyon to build that dam were the output from floating gold-extracting dredges that operated up until WWII in the area below the present dam, processing ancient river gravel that deposited down there where the Feather River velocity slowed.

Its complicated. Those hillsides surrounding the dam are likely hard enough to not erode, but a perhaps greater risk is an earthquake that shifts land along a fault line. Filling the reservoir led to a couple of earthquakes. Who knows what stresses are building with the reservoir now full.

Nice informative post, Cali.