The reconstruction of Oroville Dam’s flood control spillway is likely to cost as much as $500 million, state officials said Thursday, as design changes and unexpected additional work has inflated the cost of the project.
Originally budgeted at $275 million, the repair has grown to cover a greater level of protection for the dam’s emergency spillway – whose near failure in February sparked the evacuation of 188,000 downstream residents – as well as unforeseen problems in the bedrock beneath the main spillway, said Erin Mellon, a spokeswoman for the state Department of Water Resources.
Mellon said the state hopes to recover up to 75 percent of the reconstruction costs from the Federal Emergency Management Agency. But she said water districts that store water behind Oroville Dam, such as the Metropolitan Water District of Southern California, the Santa Clara Valley Water District and the Kern county Water Agency, will be expected to pick up whatever costs the federal government won’t cover.
Mellon said state officials have known for several months that the cost would exceed the original budget. General contractor Kiewit Corp obtained the two-year, $275 million contract in April, when the reconstruction project was still only 30 percent designed, she said.
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Mellon said a more accurate cost estimate should be available by Nov. 1.
Although the reconstruction costs have risen, Mellon noted that the cost of handling the initial emergency in February came in at around $160 million, or more than $100 million below original estimates.
The higher costs for the reconstruction came to light as officials from DWR and Kiewit led a media tour of the construction site, where 700 workers are racing to meet a self imposed Nov. 1 deadline to have the dam ready for wet weather. Although the spillway project won’t be completely finished for another 12 months, the spillway should be able to release 100,000 cubic feet of water per second during the upcoming rainy season.
“I don’t want to jinx it, but we’re ahead of schedule,” said Jeff Petersen, Kiewit’s project manager. The rain expected to hit the region late Thursday might cause slight delays but wouldn’t derail the project, he said.
Petersen told reporters that costs rose in part because workers discovered that a portion of the main spillway was built on underlying rock that was deemed unsuitable. As a result, workers had to dig a lot deeper into the bedrock than they had planned before laying the new concrete. That led to much higher costs for excavation and concrete to fill in the hole.
“We had to take that cavity out,” he said.
Petersen said the higher costs aren’t unusual for a project that has been designed and built on the fly. “When you get out on the construction site, there’s so much more information that you glean,” he said.
The dam emergency began when a giant crater erupted in the 3,000-foot-long main spillway Feb. 7 during a heavy rainstorm. Dam operators temporarily dialed back water releases to limit damage to the concrete chute, but the rains filled up the reservoir and water began flowing over the adjacent emergency spillway – an unlined hillside topped by a concrete lip – for the first time since the dam opened in 1968. When the hillside eroded so severely that it appeared the concrete lip would crumble, unleashing a “wall of water,” officials ordered the evacuation.
Problems with girding a portion of the emergency spillway with concrete have contributed to the higher costs. The original plan called for that layer of concrete to run about 300 feet down the hill from the top, ending with a massive underground wall designed to curb erosion. But the underground wall had to be moved several hundred feet further down the hill because the rock beneath the original site wasn’t strong enough. Moving the wall downhill meant doubling the size of the layer of concrete.
Although the team of forensic experts investigating why the main spillway fractured hasn’t completed its work, officials say they are confident the rebuilt structure will be stronger and safer than its predecessor.
“There’s more rebar, the concrete is stronger,” Petersen said. “There’s new technology - it’s erosion-resistant concrete.”
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Crews continue laying roller-compacted concrete in the middle of the Lake Oroville spillway, filling the erosion area to connect the upper and lower chutes in this update on the repairs at the dam. The state Department of Water Resources said last month that reconstruction of the spillway is on track to reach a Nov. 1 deadline. Department of Water Resources