Erosion has created a 300-foot-deep hole in the concrete spillway of Oroville Dam and state officials say it will continue grow.
State engineers on Wednesday cautiously released water from Lake Oroville's damaged spillway as the reservoir level climbed amid a soaking of rain.
Situated in the western foothills of the Sierra, Lake Oroville is the second-largest manmade reservoir in California after Shasta....
cranky108 - I presume the tailrace water elevation is so high because the area downstream is packed with debris.
My biggest concern with this whole situation at the moment, is with the "fucntional", non-damaged portion of the spillway. The lower portion failed at 50,000 cfs, after a relatively short period of time at that flow rate. And after not having regularly been subjected to flows like that for some time. And for an undetermined reason.
They have been "stress testing" the rest of it for some time now, and will have to do so for the foreseeable future. How long can it hold up? If there is an insidious little crack growing, or cavitation eating away at something out of sight; we won't know about it until, well, we know about it. I would imagine they would really like to have a look at it in the near future.
Otherwise everything seems about as under control as it can be at this point.
Another question. Looking at the recent posts on the Water Department web site I see a large group of workers (some volunteers) carrying buckets if road gravel in the backfill area outside of the walls alongside the main spillway. It would appear they are trying to place a graded filter between adjacent earth and cobbles forming an apparent drain system behind these walls. Any comment from those more familiar? I still need an explanation as to where the water comes from that we see spilling into the spillway from these walls. Is that water originally from a drain system under the spillway floor or collected from nearby earth and rock outside the wall area? Noting where they are placing the road gravel, maybe the latter is the source.
I don't know if Juan Browne is correct, but he stated in the video JRB linked that they will have to route the power house output in a completely new direction. Seems like that could take quite awhile depending on how far and how many towers have to be erected. Seems like it will be a long time before they can restart the power house and use it to lower the lake.
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
This video taken Tuesday 21st indicates the tail water is up 22 feet from normal due to debris at the spillway area. Looks like a long way to go before back to normal.
From what has been reported, there appears to be no way to bypass the turbines when using the main spillway. All of the water that goes into the powerhouse must pass through at least one of the turbines and without them being connected to at least some sort of ballast load, there's no way to control their speed.
IIRC you walk out the door of the plant, everything being concrete, -level concrete-,
and to the immediate right is down to the tailway water, and spreading out to the left
is the PP switch yard.
If the water is lapping at the door in then it is also lapping at all the transformers
and switchgear.
If water is being channeled through the scroll case to the turbines, unless the impeller vanes can be closed completely, the turbines will turn, generating electricity. The vanes are usually fixed though.
Two other things:
1. Debris in the downstream channel could affect the tail water elevation, and
2. Debris in the water could damage the turbines if it entered the intake.
I am a little unclear where in the project the debris cleanup is occurring that closed the power plant.
Thanks John & msquared, was wondering about the turbine over speed issue hence my term 'productively produce' and you pretty much support my concerns. I'm pretty sure none of my ideas for using up the 'spare' electricity would pass muster either
Kenat See my post above and the link. That will answer your question. Passing a bunch of water through the tribunes would over spin them without hooking to the grid, now not hooked up. However, note that the water is so high there that it is above the floor level of that area. If the wall gives way the generator sections will be under water. It now is one heck of a mess, not soon to be back to normal by any meas. I'd give it a few years at the least.
Debris is blocking the channel downstream and raising the level at the power house. Discharging water through the power house may raise the water level further.
Many years ago, an ice storm took took out a couple of towers on a 500 kV line feeding Vancouver Canada.
They brought in a couple of cranes and suspended cross arms with insulator strings in place of the downed towers.
I don't see it taking very long for a temporary connection to the grid, but anything that may raise the water level further may be the real issue with not being able to use the power plant.
Bill
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"Why not the best?"
Jimmy Carter
Oh yeah! That spillway brings a whole new scale to hydraulic mining.
They should just request gold miners to come pan the debris field requiring them to dump the dross into dump trucks. It would all be removed in about a week.
Gold is heavy, so you should expect it in the bottom of the lake. Wait for the next low water event and pan the bottom of the lake.
Many floods have been caused by not keeping creeks and streams clear of trees. The problem being that because of the water table, the trees like to grow in those low areas.
On the other hand, the debris is limiting the amount of water downstream, which maybe good for those people as long as the earth and debris dams don't break.
This item is a week old, but I can't recall anyone mentioning this specific issue previously. If they did, I apologize for offering something that has already been presented.
Mr. Baker: This is another example of non-professionals codgering up a story without checking with professionals. If you look way back on this forum you will see a likely version from me. Also look at the crummy "rock" situation at the emergency spillway and it all fits together . This whole site is crummy "rock". It hardly can be fit to be called rock. Locating a dam here based upon topography and hoping to do enough changing of what is there to make it work has failed. Let's wait for a clear explanation from those close to the situation. Let's have some expert from there explaining the presence of workers (volunteer?) on the outside of the spillway walls with buckets of road gravel apparently trying to place some filtering of water before it reaches the cobbles backfill to those walls. Why? Also where is the water coming from that squirts out from the walls into the chute? As of now this forum does not have an expert's explanation of this chute failure.
