Discussion Topic |
|
This thread has been locked |
jaaan
Trad climber
Chamonix, France
|
|
|
Feb 16, 2017 - 06:30am PT
|
Can someone just explain the problem to me as I've just not understood. The damage is to the spillway? This is on the downstream side of the dam? How does this affect the integrity of the dam itself? Thanks.
|
|
mouse from merced
Trad climber
The finger of fate, my friends, is fickle.
|
|
|
Feb 16, 2017 - 06:35am PT
|
Andy/nita, best wishes for a happy outcome.
Looking for Damzilla the Damkilla.
|
|
John M
climber
|
|
|
Feb 16, 2017 - 08:04am PT
|
Jaaan..
In the picture above, the dam is to the right. For scale, it is 700 feet tall and 6000 feet across approximately.
In the center is the main spillway. It is a cement spillway with gates at the top.
To the left is the auxiliary/emergency spillway.
First.. the main spillway developed a hole in it about halfway down.
The dam operators were concerned the hole would grow and possibly erode back to the main spillway structure and possibly even take it out. There was also concern that as it erodes the hillside out, it could erode back towards the main dam.
So they stopped flow to inspect. Meanwhile the water was rising in the lake.
there is an emergency spillway which is I believe an earthen structure capped with cement which is designed to have water flow over it like a weir. There is no gate. It is approximately 30 feet tall. In examining the hole in the main spillway the operators decided to use the emergency spillway. They let the water rise until it topped the emergency spillway. Erosion started happening downstream of the spillway. This erosion started working its way back towards the base of emergency spillway and the concern was that it would eat out the base of the spillway causing it to fail and thus allowing 30 feet of lake to rush out.
So the operators reopened the main spillway to stop the use of the emergency spillway.
There are now two main concerns.
1. will the main spillway continue to be useable? It seems to have stabilized somewhat, but with so much water flowing over it, no one can tell if its being undercut.
2. Can they repair and harden the emergency spillway enough so that if the main spillway starts to fail they could use the emergency spillway.
There is a whole lot more to the story such as there was a lawsuit 10+ years ago asking them to harden the downstream side of the emergency spillway. But they didn't.
We still have a lot of winter to go.
|
|
Sula
Trad climber
Pennsylvania
|
|
|
Feb 16, 2017 - 08:25am PT
|
The damage is to the spillway? This is on the downstream side of the dam? How does this affect the integrity of the dam itself? Normally, the primary spillway carries the water ~3000' (and ~700 ft vertically) to the river below. Because of damage, much of that water currently exits that concrete spillway early, and has caused significant erosion on the face of the dam (though it's very far from causing the dam itself to fail).
The emergency spillway consists of a concrete wall, but no concrete channel - the water just flows down the face of the dam, eroding it. That erosion had started to undermine the concrete wall. If this were to fail, the top ~30 ft of the lake would rush out through the gap, which represents a huge amount of water flooding Oroville and other communities downstream.
The primary spillway is still draining the lake at a rate of 100,000 CFS - the aim is to reduce the lake level enough that it will handle inflow from rain and snowmelt without again reaching the height of the emergency spillway. There's no possibility of repairing it until the flow can be stopped (for a long time), which won't happen soon.
Lots of work is being done to reinforce the area near and below the emergency spillway, so that if it should again be needed it will not be undermined.
|
|
Ed Hartouni
Trad climber
Livermore, CA
|
|
|
Feb 16, 2017 - 08:34am PT
|
from the document I linked far up-thread:
FERC spillway guidelines distinguish three specific classifications of spillways: service spillways which "should exhibit excellent performance characteristics up to the 1% chance flood event" and could exhibit more "marginally safe performance characteristics for the inflow design flood" (usually the probable maximum flood), auxiliary spillways designed for infrequent use and could sustain limited damage during the inflow design flood, and emergency spillways that because of their infrequent use it is acceptable to sustain significant damage. ("Selecting and Accommodating Inflow Design Floods for Dams, FERC, October, 1993.) ...
|
|
john hansen
climber
|
|
|
Feb 16, 2017 - 08:38am PT
|
Has anyone seen any photos of progress they have made placing those bags below the emergency spillway?
|
|
tuolumne_tradster
Trad climber
Leading Edge of North American Plate
|
|
|
Feb 16, 2017 - 08:47am PT
|
https://www.metabunk.org/oroville-dam-main-spillway-waterfall-erosion-watch.t8402/
The latest from the Metabunk blog...
"parallel erosion channel sharply cutting into the hillside directly left of the waterfall" is referring to the flow (new) that can be seen to the left side of the left wall on the main spill way. It is shown clearly in the attached photo (very high definition and very useful). Also note the small stream of water just further to the left of the wall.
If this continues it will probably just lead to a widening of the fan below the waterfall, and the continued destruction of the structure of the lower parts of the spillway (already pretty much a total loss)
Looks like the 2 electrical power line towers to the left of the damaged spillway are at risk...there are plans to fly the towers out by chopper once there is time/availability/cooperative weather.
Here's a closer look at the flow out of the left side of the main spillway...
|
|
healyje
Trad climber
Portland, Oregon
|
|
|
Feb 16, 2017 - 10:51am PT
|
With regard to the brown river water and there being no clear turbine effluent coming from the dam:
Officials had said they would start throttling back the releases to resume pulling debris from the river channel beneath the dam. The debris has backed up the river at a critical point, preventing the state from restarting the dam’s hydroelectric power plant. The plant would be capable of releasing up to 13,000 cfs.
|
|
cleo
Social climber
wherever you go, there you are
|
|
|
Feb 16, 2017 - 11:06am PT
|
|
|
cleo
Social climber
wherever you go, there you are
|
|
|
Feb 16, 2017 - 11:11am PT
|
A look at the lithology:
Left - metamorphic, looks like greenschist (?), hard rock (not choss)
Right - Colluvium (slope soil) and Pyroclastics, tuff, or sandstone - (choss). This canyon is ~200 feet deep and formed in 3-4 days of ~40,000 cfs.
|
|
labrat
Trad climber
Erik O. Auburn, CA
|
|
|
Feb 16, 2017 - 12:59pm PT
|
"Can someone just explain the problem to me as I've just not understood."
The third post in this topic by Dingus explains it well. Go back to page one......
"ALL dams in California are "flood control" dams, it is the only way they get federal financing."
Not completely true. California also has debris / sedimentation dams that were put in place to try to stop material from coming down to the valley from the gold mining era. Englebright dam is a good example of this.
https://en.wikipedia.org/wiki/California_Debris_Commission
The balancing act of reservoirs is interesting. If you want to keep up with lake levels, inflows, and outflows I suggest monitoring this page.
http://cdec.water.ca.gov/cgi-progs/current/RES
I find it interesting that Shasta is being kept so high and wonder if this was to keep pressure off the levees downstream from Oroville.....
|
|
labrat
Trad climber
Erik O. Auburn, CA
|
|
|
Feb 16, 2017 - 01:21pm PT
|
This PowerPoint presentation on history of dams in California is great!
Warning, it takes quite a bit of time to load.
http://web.mst.edu/~rogersda/dams_of_ca/Dams-of-California-Presentation-2012.pdf
|
|
jaaan
Trad climber
Chamonix, France
|
|
|
Feb 16, 2017 - 01:55pm PT
|
Ok thanks. Makes more sense now.
|
|
BigB
Trad climber
Red Rock
|
|
|
Feb 16, 2017 - 02:37pm PT
|
5 days of rain starting today
|
|
BooDawg
Social climber
Butterfly Town
|
|
|
Feb 16, 2017 - 02:52pm PT
|
One "atmospheric river" is expected to hit So Cal tomorrow (Friday).
Another is expected to hit the Oroville Dam area on Monday. It's said to be warm and will probably yield mostly rain and relatively little snow, meaning quick run-off and possibly VERY BAD NEWS.
http://weatherwest.com/archives/5582
|
|
Ksolem
Trad climber
Monrovia, California
|
|
|
Feb 16, 2017 - 03:25pm PT
|
Thanks LabRat. Very interesting.
|
|
Jon Beck
Trad climber
Oceanside
|
|
|
Feb 16, 2017 - 03:38pm PT
|
This canyon is ~200 feet deep and formed in 3-4 days of ~40,000 cfs.
Grand Canyon by comparison was eroded in about a million years, pre-dam flows were 100 cfs. Current flows are about 20 cfs, although they have run as much as 48 cfs as an experiment.
|
|
cleo
Social climber
wherever you go, there you are
|
|
|
Feb 16, 2017 - 03:45pm PT
|
you mean 100,000 cfs, 20,000 cfs, and 48,000 cfs?
It's a big canyon (at Oroville) to have developed so quickly - says something about the material in the hillslope, which appears to be more soil-like than rock-like.
|
|
Impaler
Social climber
Oakland
|
|
|
Feb 16, 2017 - 04:34pm PT
|
Here's a good video about how things go down when it hits the fan. This is the Auburn Upstream Cofferdam Failure from 02/18/1986. Starting around 2m40s it gets going, then check out around 4m into the video the accelerated rate of erosion and soil continuously falling down.
[Click to View YouTube Video]
|
|
|
SuperTopo on the Web
|
Let us know!