Maybe I missed something, and would appreciate clarification from those who are more astute, but it appeared to me that DWR is planning work on 4 separate projects: 1) the emergency spillway, 2) the main spillway gates, 3) the remaining section of the upper main spillway, and 4) the lower main spillway.
For the emergency spillway, they are planning on going some indeterminate distance below the existing weir to where they can dig down to “blue bedrock”, put in a cutoff wall, and fill in between the wall and weir with roller compacted concrete, as well as use RCC for some indeterminate distance below the wall. I’m certainly no expert, but I assume to place roller compacted concrete, you’d need a flat enough surface to roll upon. Wouldn’t they first need to fill in and smooth out a lot of the rough surfaces they just made with uncompacted rock and concrete before they could use RCC?
To work on the main spillway (FCO) gates, wouldn’t they have to get the lake level below the gates first and keep it that way using only the Hyatt powerhouse? It seems that they’d have to wait to start until they were sure the total inflow to the lake would stay under 13k cfs, which may not be until late this summer.
They plan to “upgrade” the remaining upper main spillway so it can handle 270k cfs. Wasn’t the original design specification for 270k? Aren’t they implicitly admitting that the spillway wasn’t up to spec?
My understanding is that they plan to work on the lower (missing) spillway section in 2 phases. This year, they plan to knock back and stabilize the massive side slopes of the new ravine to ward off further erosion, and to place some concrete in the plunge pool to channelize flow so that the the ravine can better handle up to 100k cfs. Next year, they plan to use RCC to rebuild the lower spillway up to it’s original height so that it too can handle 270k cfs. This would make the nations tallest earthen dam with perhaps the world’s tallest concrete spillway.
Am I missing something in their plan?
This is a tough nut to crack. No matter what they do, it ain’t going to be easy. An once of prevention could have saved a few killotons of cure.
The “roller compacted concrete” confuses me as well.
It is a concrete mix that is laid down in a thin layer
and compacted by a steam roller, similar to the way
asphalt is laid-down for highway pavement.
I don’t understand how that is done on a non-level surface.
RCC placement requires a relatively flat surface, but since it is typically placed in 1 foot layers, the irregularities of the surface may be tolerated to a % of the thickness and the resulting roller compaction level grade results. Steel Drum or Rubber tire roller compactors are used in the compaction. Then successive layers are compacted quickly as the material is analogous to asphalt (zero slump, i.e. compresses hard with compactor roller in contrast to sloppy concrete pours).
The Spillway dispersal chute (end of spillway) was designed for 296,000 cfs. So they won't have to do any redesigning of the existing Feather river junction and opposite side bank.