Reconstruction of the lower part of Oroville Dam’s spillway is on schedule, the state and its contractor said Wednesday.
The spillway will be able to handle releases of 100,000 cubic feet per second if needed on Nov. 1, according to representatives of the Department of Water Resources, the Natural Resources Department and Kiewit, the contractor doing the work.
About 2,270 feet of spillway has been demolished, and it will be rebuilt this year with a combination of structural concrete and roller compacted concrete. The latter doesn’t have as much reinforcement but is “acceptable in spillway and dam construction,” according to Erin Mellon of the National Resources Department, the communications manager for the project.
A topping of structural concrete will be placed over the roller compacted concrete next year. The top 730 feet of the spillway, which is just being patched this year, will be demolished and replaced as well in 2018.
What people looking at the webcams showing the construction are seeing now is the placement leveling concrete on the bottom 350 feet of the spillway. Structural concrete will be placed over that. The same construction technique will be used on the top 870 feet of the spillway to be reconstructed this year as well.
The space between — 1,050 feet — will be filled with roller compacted concrete. It is already being used to fill the deepest void that was gouged out from beneath the spillway, according to Jeff Petersen, Kiewit’s project director, and use of that material should become visible on the webcams soon.
He said construction of the walls on the sides of the spillway should begin in the next couple of weeks.
The final construction plans for this year were approved last week by the Federal Energy Regulatory Commission and the state Division of Dam Safety, according to DWR project manager Ted Craddock, who called that a milestone.
Petersen said Kiewit has removed 23,000 cubic yards of old concrete and excavated 332,000 cubic yards of earth and rock so far, which is about 80 percent of what will eventually be necessary.
At the bottom of the spillway, 7,000 cubic yards of leveling concrete has been poured, and the first 560 cubic yards of what will eventually be 330,000 cubic yards of roller compacted concrete have been placed.
More than 100 people are working on the spillway, day and night.
He said pouring so much concrete during this unusually hot summer is a challenge, but the concrete is made with ice rather than water. “We also have liquid nitrogen available if necessary,” he said.
DWR has approval to draw the Lake Oroville surface level down to 700 feet of elevation by Nov. 1, which Mellon called more conservative than usual. That’s to allow room for storm runoff, because although the spillway will be ready for use Nov. 1, they’d clearly rather not use it this year.
For the last 10 years, the lake level on Nov. 1 has fluctuated between 856 feet in 2011, to 657 feet in 2014, according to the DWR website. The average for those 10 years on Nov. 1 was 726 feet.
Joel Ledesma, deputy director of the State Water Project, said it was too early to say whether drawing the lake down to 700 feet would have any impact on water deliveries in 2018.