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....
What is wrong with building a new spillway away from the old one - would that not allow the old spillway to operate if the new one is (inevitably) delayed in completion?
Bill Croyle, acting director of Department of Water Resources, explains the current plans to fix the Oroville spillway and the emergency spillway. Video by Randy Pench Produced by Sue Morrow
OROVILLE
State officials sketched a two-year recovery plan Thursday for the battered Oroville Dam spillway, revealing a blueprint that's far from complete, still in need of a price tag and certain to leave the structure partially damaged as the next rainy season approaches.
The plan unveiled by the Department of Water Resources will proceed in phases and won’t be finished until 2018. Notably, the giant ravine that's been carved out of a nearby hillside, the result of water boiling out of the fractured spillway in recent weeks, could be used again next winter to handle excessive water releases.
Nonetheless, Acting DWR Director Bill Croyle said the 3,000-foot-long chute will be functional next winter.
The repair plan was released nearly two months to the day after a giant crater erupted in the dam's main spillway, eventually triggering a crisis that forced the temporary evacuation of 188,000 residents.
Croyle acknowledged the plan is a work in progress.
“We have a little less than a 60 percent design,” he told reporters. Nonetheless, the project is being circulated among four contracting firms, and DWR expects to execute a contract by April 17. The firms weren’t identified.
“We’re moving as fast as we can. We need this (contract) in a matter of hours or days, not weeks or months,” Croyle said.
Croyle said he was unable to provide a cost estimate beyond his original projection nearly two months ago that it would take up to $200 million to repair the structure. President Donald Trump made a disaster declaration over the weekend that’s expected to free up approximately $274 million in federal funds for Oroville repairs, although much of that money is being spent on debris removal and other functions not directly tied to repairing the spillway.
Gov. Jerry Brown moved to expedite the project Thursday, signing an executive order that waives state environmental laws and other red tape. Nonetheless, Croyle said DWR will be as sensitive as it can to environmental issues as work progresses.
The crater that erupted Feb. 7 essentially split the concrete spillway in two. Water gushing down the spillway, misdirected by the giant chasm, carved an enormous ravine in a nearby hillside.
Croyle said DWR plans to leave the ravine in place this year. It could serve as a kind of auxiliary outlet in case the reservoir is rising too high and the concrete structure, despite its repairs, can’t handle excessive water flows.
The lower spillway itself will be “demolished and replaced” over the summer, said DWR chief engineer Jeanne Kuttel. “It will be stronger than it was before,” she said. The state plans to use quick drying “roller compacted concrete” on the lower portion of the structure, she said.
Croyle and Kuttel said the upper portion of the spillway, although undamaged, might be partially or completely replaced this summer as well. However, recent geotechnical studies have shown much of the upper spillway is thicker than previously believed, and might not have to be replaced, Croyle said.
Croyle acknowledged that plenty of work will be left over to 2018. That includes building higher retaining walls alongside the concrete chute to handle extremely high flows.
OROVILLE MAIN SPILLWAY REPAIR PLAN
Multiple designs remain under consideration because of uncertainty about how spring weather will affect the construction timeline.
Diagram of spillway repair plan Source: Calif. Dept. of Water ResourcesNATHANIEL LEVINE nlevine@sacbee.com
Meanwhile, he said DWR plans to partially line the adjacent emergency spillway with concrete this summer – a first for the structure.
The emergency spillway turned out to be the weak link in the February near disaster.
After the main spillway fractured, it was shut down temporarily for inspection. Inflows from a heavy rainstorm spiked water levels at Lake Oroville to unprecedented levels, and water poured over the emergency spillway – a concrete apron perched atop a hillside – for the first time since the reservoir opened in 1968.
A day later, engineers discovered that the hilllside was eroding so badly that the concrete apron might crumble, unleashing a “wall of water” into the Feather River below. That sparked the evacuation of 188,000 downstream residents Feb. 12 until lake levels receded and the situation stabilized.
Butte County Sheriff Kory Honea, who ordered the evacuation, said he was encouraged with the progress on the repairs. “We’re moving from an emergency crisis management mode to a recovery mode,” he said. “We are in a much, much better position today than we were on Feb. 12th.”
Croyle said DWR, in consultation with the sheriff, won’t make bid documents public because they’re considered “critical energy infrastructure information,” and could be used to create “harm and havoc.” DWR cited the same explanation for sealing several investigatory documents with the Federal Energy Regulatory Commission last month. FERC licenses the dam and is overseeing the repair effort.
An earlier document, from a team of consultants hired by DWR to advise on the repairs, said fixing the spillway in one year would be nearly impossible because of design flaws and the severity of the damage. The report was the first sign that repairs would continue beyond 2017.
Croyle said that first report “shouldn’t have been made public” and DWR will make sure future reports by the consultants stay sealed.
Paul Tullis, an engineering consultant from Utah who has studied spillway designs, said DWR's approach to the repairs seems reasonable, given the impossibility of completely fixing the structure in time for the next rainy season.
"There's only so much they can repair in a half a year or so," Tullis said. "They can only do what they can do."
Tullis said it will be critically important to monitor the hillside next to the main spillway next winter if DWR has to let more water flow through the recently-carved ravine. If too much of the hillside gets washed away, it could potentially harm the earthen wall of the dam itself, he said.
The spillway has been shut off since March 27 for temporary repairs. As raindrops fell outside the giant tent where he briefed reporters, Croyle said he believes the upcoming storm won't raise lake levels to uncomfortable levels, even with the spillway not releasing any water.
He added that the spillway will probably be used once or twice more this spring, depending on how heavy the runoff gets as the Sierra snowpack melts. Before long DWR plans to shut it down for good to begin the major repairs.
"does anyone here actually believe the earth below wouldn't be eroded as that much water washed uncontrolled over that area?"
That presumes that it's "earth." The dam itself is earth-filled, but the spillway is on part of the original landscape, which is rock, some crumbly, some not.
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!
I am using this definition. Earth - the solid matter of this planet making up the surface. Is that good or is more nitpicking necessary?
Whatever you wish to call the earth/rock/soil/dirt in that area, it quickly eroded both when the main spillway failed and while water flowed over the emergency spillway. To me, it seemed rather obvious that it would also erode if a 30' high wall of water 1700' long started washing over it, leading to far more water then the often quoted 30' actually being released.
A Report by Robert Bea of the Center for Catastrophic Risk Management at UC Berkeley gives a few reasons for the failed spillway. Design, construction, and maintenance defects and flaws where all blamed in the preliminary report. Lots of good pictures and analysis in the report.
Page 3-160 is very interesting because Oroville get very very hot.
There is a wealth of information in the Bureau's document because it shows other failures. I worked on the construction of the spillway of Mangla Dam in 1963-64, but don't know what the spillway thickness was. Tarbela Dam which was constructed a few years later appears to have had a spillway thickness of 24".
On page B-9 is the cavitation damage at Glen Canyon spillway tunnel. I had not seen this before but our firm provided the design for the work platform on the slope (Guy F. Atkinson project). For some reason I was told that the damage was in the ceiling so seeing the damage at the bottom of the tunnel was a unpleasant surprise.
Well, if this was now my job, I would do the following. First off to my computer. Take the current spillway design and load it into a amazing program called 3D-FLOW (I am not working for them, heheheheh)and draw profiles at different flow rates. Then get the optimum design pattern which give satisfactory results where cavitation is none and water speeds do not go beyond 12 to 15 meters per second by playing with aerators positions and quantity. Then start at base level and get a smooth foundation level(specialist blasting methods is capable do that relatively very quick. Fill all voids with compacted and tested soil at max compact resistance. Dowels should form a inverted u shape. Redesign the spillway according to the profiles drawn up in 3D, and add a mix of around 6 kg 50 mm macro fibre per cubic meter concrete. Additional to my steel schedule. Lots of concrete and steelbut no brain drainer and not a complicated construction. Most important, keep your water flow rate below 12 m/s while still accommodating the flow capacity. In short and basic. The in-between cosmetics will land on the table of the structural engineers to sort out. I wish my company was close by. This is a nice project.
I'd just add lots of concrete to the new right channel in the spots that dirt still exists and call
it a day. That would reduce the prep time to almost nothing so they could complete it all in a month
or two. It would look naturally great and there won't be any cavitation since the water breaks
somewhere about every 5 feet.
"To help with the design, the separate team investigating the spillway failure sent California water officials and Utah hydrologists a list of factors they've found that could have contributed to the failure - many focusing on the condition of the spillway's concrete, slab joints and foundation. But no one factor has been discovered yet to determine how the failure happened, said John France, a dam engineering consultant leading the California investigation."
Yes, the repairs are already underway. My wife flew out to the site shortly after the repair contract was awarded to help get things kicked off. The state is fast-tracking the entire process (as they should).
