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....
It was doubly bad because when the water hit the break, it also went sideways and took out the terrain on the right side of the spillway, which allowed the hillside under the spillway a much easier egress from under the spillway
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!
After looking at the latest photos, I was thinking the same thing. If all of the loose rocks and debris has been washed out and they get the basin opened-up and the water level drops to the point where they can start to release water through the main spillway (through the turbines in the powerhouse) perhaps there might not be a need for a completely reconstruction secondary spillway. But then I'm not a civil engineer so I'll leave that to the professionals.
What you see is technically the "main" spillway, the operative word being "spill" The turbine waterway is typically limited to very low flow, only enough to turn the turbines. The typical requirement is that it needs to be as low as possible while still providing adequate for whatever is needed downstream, whether it's keeping the delta dart alive, or provide irrigation water for farmers.
The spillway, on the other hand, is to keep the reservoir from overtopping the dam
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!
After weeks of blazing 50kcfs the erosion seems to have reached a static situation. Why
not just concrete in the few remaining areas that look erodable instead trying to refill
and re-create the original poorly functioning spillway?
Some of the comments remind me of a solution one university had to pathways in a new section of campus... they let the students walk wherever they wished for several months, then they put in concrete paths along the areas where the grass was worn away.
Some of the comments remind me of a solution one university had to pathways in a new section of campus... they let the students walk wherever they wished for several months, then they put in concrete paths along the areas where the grass was worn away.
My alma mater, North Carolina State University, followed that philosophy. Knowing what battles to take on with mother nature, and when to let her have her way, is an important piece of wisdom for any engineer.
The arm chair thoughts also were mine until I looked at the close ups to just leave it as is. The gray rock appears competent and holds pretty well, but that material that is brown color does not. Leaving things as they sit now may well get erosion backing up toward the inlet. That was the concern at the emergency spillway, possibly still not well reinforced. Maybe the water department had better bite the bullet and do it right this time. Enough information was there when they originally built to avoid this. Now there is a second chance to do it properly.
Looks like they need to do some selective blasting to me to create a viable channel that is stable and can be maintained. Use of some high pressure grouting would be in order too with all the fracturing.
Just found part 2 of the DWR video above, which has a little closer view of the geology surrounding the primary spillway and distant shots of the work beginning to get the down stream channel cleared so the generators can be restarted.
More arm char thoughts. That delta appears to the harder chunks from the gully areas. I'd first do some soundness tests on representative chunks. If it meets specs for concrete, then set up a crushing plant, sieving and then a concrete batching plant, possibly on the side hill between the main spillway and the dam. Maybe an aggregate washing plant also. Then rig a cable system from there to the gully. Heck, that would take care of the disposal problem and serve as an aggregate source. The stuff probably has had all the soft parts washed away. Right now playing around with a dozer or two and a back-hoe to try to open a channel isn't going to really do the job needed for a good fix. It would be nice to see a well thought out plan.
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