It’s a few months shy of two years since a hole was ripped into the main spillway at Lake Oroville and 10s of thousands of downstream residents were evacuated for fear a portion of the emergency spillway might give way and send out a wall of water.
Over a billion dollars later, crews have finished heavy construction on the main and emergency spillways, officials announced Wednesday.
Thursday marked the self-imposed deadline set by the Department of Water Resources to finish the project’s main construction. Construction crews will remain active in the area through the winter conducting joint sealing, drainage work and site cleanup, but the bulk of the work has been completed.
“We met our milestone about a week ahead of schedule,” said Tony Meyers, DWR project manager for the recovery phase of the work.
Meyers said the main spillway’s final erosion-resistant slab was placed earlier this month, three weeks ahead of schedule. The final piece of the upper chute and energy dissipators on the lower chute were placed a few weeks ahead of schedule.
As for the emergency spillway, the roller-compacted concrete splash pad and buttress were completed last week, leaving only a concrete cap that connects the buttress and emergency spillway together left to complete – likely by the beginning of 2019.
Jeff Petersen, executive project director for Kiewit Infrastructure West Co., highlighted just how much work has been done at the reservoir over the last two construction seasons.
In terms of the concrete placed on the main spillway, he said there would be enough to stretch from Oroville to Amarillo, Texas; enough steel to stretch from Portland to San Diego; enough drainage pipe to stack up to 10 miles high; and enough RCC on the emergency spillway to cover an area of 1.2 million square feet, or 25 NFL football fields.
“Rebuilding the spillway has been a massive undertaking, and I’m proud of our accomplishments,” Petersen said.
The spillway will be officially ready to go on Dec. 1 because the concrete still needs to cure, but if it was needed before then it could be used, said Erin Mellon, assistant director of Public Affairs for DWR.
The state department has kept the reservoir’s storage capacity low in order to make sure the spillway doesn’t need to be used. Mellon said there is about 120 feet of storage capacity left before it would be needed.
The new main spillway has the capacity to release up to 270,000 cubic feet of water per second, though it’s unlikely that amount would ever be released as the channel downstream only has the capacity for 150,000 cfs.
“As Lake Oroville enters its post-construction phase, the safety of the dam and other structures, as well as the safety of the downstream communities will remain a top priority,” said Joel Ledesma, deputy director of DWR’s State Water Project.
Mellon said the most recent cost estimates for the entire project – both the initial emergency response and reconstruction efforts – indicates a total price tag of approximately $1.1 billion. Of that, Kiewit received $630 million, recovery activities accounted for $310 million and the initial response cost approximately $160 million.
The main spillway was damaged in February 2017 by water being released out of the reservoir during a significant storm event, prompting officials to turn off releases. The lake’s elevation began to rise and the emergency spillway structure had to be used for the first time in its history, but water began to erode the hillside. With the threat of flooding and the potential loss of the secondary structure, officials turned back on the main spillway further damaging the structure.