Expert consultants are now revealing what should have been figured out years ago. Soon, there will be hard questions asked as to why these issues were not figured out and fixed when they had the opportunity. This article provides more detail on the "spillway design flaw" revelations from experts.
BTW - NO Bentonite clay was used. The "Clay" usage was from "surface grade filling in depressions" in doing the original construction.
Damage, design flaws in Oroville Dam spillway point to lengthy repairs, consultants say
Article clips: (emphasis mine)
1. "Above the crater, consultants described design problems in the intact portion of the chute that are so “gross and obvious” they will have to take priority this year, said J. David Rogers, a dam expert from Missouri, who reviewed the report at The Sacramento Bee’s request. Rogers said the problems the consultants described were so egregious he was surprised the spillway didn’t fail decades ago.
2. "It calls into question the whole design of what’s still there in the upper section,” said Rogers, a professor at the Missouri University of Science and Technology."
3. "The report contradicts DWR officials’ assertions that the 3,000-foot-long spillway can be completely repaired in time for the next rainy season."
4. "The expert panel’s conclusions, based on a review of reports and an on-site inspection earlier this month, provide a first-ever accounting of structural and design problems that might have caused the spillway to essentially split in half Feb. 7."
5. "The consultants described seeing troubling amounts of water flowing from underneath the structure, concrete that was far too thin and dangerous gaps underneath the foundation on which the massive concrete chute sits."
6. "Notably, the panel expressed concern that the concrete chute is only a foot thick, and less so in some places. DWR built the spillway on an uneven mountainside and in some spots used compacted clay to fill in the depressions in the rock foundation beneath the concrete. The consultants described finding evidence of “a number of repair instances” in which portions of the chute were cut away in order to “fill voids beneath the concrete.”
7. “This calls into question whether the portions of the slab that appear undamaged by the failure should be replaced during the restoration,”
8. "The panel report also said that while touring the spillway, consultants spotted “extraordinarily large” amounts of water gushing out of drains designed to move water out from beneath the intact portion of the chute. The water was flowing even though the spillway’s gates were closed and it wasn’t raining,.."
9. "Paul Tullis, a dam safety consultant ... agreed that it found the original design and construction inadequate."
DWR's response to the FERC expert consultants statements:
10. "Bisnett, the DWR spokeswoman, said the agency plans over the long haul to “rebuild or replace” both spillways “with the latest design, technology and materials, with public safety as our top abiding concern.” She added that the main spillway “met the design and construction standards of its time half a century ago. Through the decades, the spillway has been inspected repeatedly and been found to be well maintained and satisfactory for continued use.”
I'm sure the experts will have something to say about "competent" recognition of alarming conditions (seemingly a non-issue with CA inspectors) - the money quote: "the spillway has been inspected repeatedly and been found to be well maintained and satisfactory for continued use".
Temporary Fix For Oroville Dam Spillway Could Involve Making Water Jump Gap
By Drew Bollea
March 23, 2017 11:10 PM
SACRAMENTO (CBS13) — Officials with the Department of Water Resources are mulling over temporary and permanent solutions to the Oroville Dam Spillway crisis. They were presented with the findings from a group of engineering experts who analyzed the problems and potential fixes to the beaten and battered spillway.
“I think it’s one of the most urgent infrastructure things you could imagine,” said Jay Lund, a civil engineering professor at UC Davis.
Lund read over the panel’s report, which outlines issue with the spillway and suggested solutions.
“They point out that there is potential for additional things to go wrong on the remaining portion of that spillway,” said Lund.
“It’s a minor miracle that it’s working pretty well given its state,” he continued.
The panel identified faulty piping, deteriorated concrete, and cracks that may have weakened the spillway foundation. Now they’re proposing some unique solutions.
One temporary recommendation is building an angled flip just above the collapse site. If water needs to be released from the lake down the spillway, the flip would launch the water away from the hole, preventing further erosion.
“I think it makes a lot of sense,” said Lund.
Lund says it’s a typical practice at other dams, but this would likely be the first attempt to jump a hole.
“They’re not holding back,” he continued.
A spokesperson for the Department of Water Resources says “We are in the process of analyzing alternative approaches, both temporary and permanent”
Experts are suggesting a two-phase solution. A fix through this year, with a complete rebuild of the main spillway in the future.
“It’s just a matter of how much time it takes and to what expense you want to go,” said Lund.
From the article :
“8. “The panel report also said that while touring the spillway, consultants spotted “extraordinarily large” amounts of water gushing out of drains designed to move water out from beneath the intact portion of the chute. The water was flowing even though the spillway’s gates were closed and it wasn’t raining,..””
Now, where would that water be coming from?
From under that rectangular object right behind the main spillway gates?