Oroville – The state Department of Water Resources Thursday outlined its plans for repairs and replacement of the Oroville Dam spillway by Nov. 1, with the undamaged top chute as the priority.
At an afternoon press briefing, DWR Acting Directory Bill Croyle said the lower portion of the spillway would also be repaired by Nov. 1 to withstand a maximum outflow of 100,000 cubic-feet per second.
The department wants to repair the top chute because the upper spillway impacts the bottom portions. However it might not end up being replaced as design plans are still fluid, Croyle said in response to a reporter’s question.
“That’s part of the risk assessment we’ve done,” he said. “We have new information this last week so we’re re-evaluating our approaches.”
The department is accepting bids for the project until April 12 and expects to begin executing those plans April 17.
Because repairing the Oroville Dam has been declared a federal emergency, the department has to jump through fewer hoops to get replacement plans approved and enacted.
“We need this in a matter of hours or days instead of weeks and months,” Croyle said. “This is the kind of project that would take two or three years to design and two or three years to (construct). We’re going to do this in about nine months.”
As the department switches into recovery mode, it’s looking at three phases going forward, with about 60 percent of the design complete, Croyle said. DWR plans to repair and replace the top part of the spillway by next winter, allowing for a total outflow of 270,000 cfs, said Jeanne Kuttel, DWR chief engineer.
That includes drains, walls and some foundation rock, in order to meet modern dam design standards, Kuttel said. The next phase will focus on the lower spillway, which will be replaced with stronger concrete. Roller-compacted concrete, or RCC, is used at dams across the nation, she said. The department expects to have bottom portion of the spillway able to handle 100,000 cfs by Nov. 1, so that would be the maximum capacity for the structure for the season.
Next year, the department plans to bring the lower chute capacity to match the top portion’s capacity of 270,000 cfs, Croyle said.
The third phase will involve reinforcing the emergency spillway with RCC.
“Our intent is to not have to use emergency spillway again but we know mother nature throws a lot at us so were going to be ready,” Kuttel said.
DWR didn’t anticipate ever having to use the emergency spillway, yet it had to for the first time in February, prompting the immediate evacuation order for nearly 200,000 people. The contingency plan, should the updated main spillway fail, is to let water run down the sides of it, where ravines have formed.
Citing security concerns, Kuttel said design plans could not be made public.
In response to a question from this newspaper, Croyle said Board of Consultants correspondence being made public would be a decision of the Butte County Sheriff’s Office because of security issues. He said the first memorandum should not have been posted online.
Croyle commended Butte County Sheriff Kory Honea for hosting evacuation plan informational meetings to inform the public of evacuation plans and announced DWR will be hosting a series of its own community meetings. The first will take place 6-8 p.m. April 27 at the Butte County Fairgrounds in Gridley. Public safety remains the top priority, he said.
Honea said the fact Croyle spoke first at the press briefing Thursday was a good sign.
“It demonstrates we’re moving from an emergency crisis management mode into recovery mode,” he said.
The Sheriff’s Office will continue to monitor risks, continue with briefings by DWR and other agencies and aid in determining how to release design information to the public, Honea said.
“In the wrong hands, they could be used to create havoc or harm,” he said. “I want to make sure there is an appropriate balance in launching that. I don’t want anything out there that might cause a problem down the road but I also want to be sure our community is aware of what’s going on.”
With the spillway still turned off, inflows were reported at 13,262 cfs by the department in an incident update report issued Thursday morning. Croyle said the department expects to use the spillway one or two more times this season.
Lake Oroville was at 844.8 feet, with the top of the emergency spillway at 901 feet. The Hyatt Powerplant was releasing 10,000 cfs, as of Thursday morning. One out of six turbines in the plant remains out of commission.
To date, 1.5 million out of 1.7 million cubic-yards of debris have been removed from the Diversion Pool, according to the department.
DWR did not have any new cost estimates for reporters Thursday.