OROVILLE, Calif. (CBS13/AP) – State engineers on Thursday discovered new damage to the Oroville Dam spillway in Northern California, the tallest in the United States, though they said there is no harm to the nearby dam and no danger to the public.
Earlier this week, chunks of concrete went flying off the spillway, creating a 200-foot-long, 30-foot-deep hole that continued to grow Thursday.
As a precautionary measure, the Oroville City Elementary District, Oroville Union High School District, Palermo Union School District, and Thermalito School District will be closed on Friday.
Engineers don’t know what caused what state Department of Water Resources spokesman Eric See called a “massive” cave-in that is expected to keep growing until it reaches bedrock.
But faced with little choice, the department resumed ramping up the outflow from Lake Oroville over the damaged spillway to partially keep up with the torrential rainfall flowing into the reservoir from the Sierra foothills.
The lake was rising at a half-foot per hour Thursday as the inflow peaked at 121,000 cubic feet per second, officials said at a news conference about a mile from the spillway. They were releasing water at about 40,000 cubic feet per second.
That’s not enough to keep the lake from continuing to rise, officials said, but is expected to keep them from having to use a nearby emergency spillway that has never been used since the dam was dedicated in 1968, when Ronald Reagan was governor.
As a backup plan, state workers and contractors were pulling out trees and bushes by the roots from the emergency spillway to keep them from floating downstream.
Officials said the critical flood-control structure is at 90 percent of its capacity. But the dam is still safe and doesn’t threaten communities downstream.
“The integrity of the dam is not jeopardized in any way because the problem is with the spillway and not the dam,” See said.
Department spokesman Ted Thomas spoke Thursday to quell speculation.
“Despite rumors, the spillway has not collapsed,” he said at midafternoon. “It’s one of those social media things.”
If the department can’t keep using the eroded concrete spillway, Lake Oroville would naturally flow over an ungated concrete crest into the mostly unlined emergency spillway once the reservoir reaches 901 feet elevation. The reservoir came within a foot of flowing over in January 1997.
Meanwhile, workers at a state hatchery for California’s native Chinook salmon loaded up all the baby salmon into tanker trucks Thursday afternoon to try to save them from the mud, concrete chunks and other debris coming their way from the crumbling spillway.
The hatchery, on the Feather River, is vital to the survival of the state’s native chinook salmon, whose numbers have dwindled during the drought. Hatchery managers planned to take the tiny young salmon to another holding point they hoped was far enough away.
The department continued to operate hydraulic power plants both at the base of the Oroville dam and downstream, Thomas said, with contingency plans in place to protect them. If they have to be shut down, which is not anticipated, he said state power managers would draw from other sources on the interconnected electrical grid.
Lake Oroville, in Butte County, is a central piece of California’s government-run water delivery network. It is used to supply water, generate electricity and for flood control.
Associated Press writers Kristin J. Bender and Ellen Knickmeyer contributed to this story from San Francisco.
Copyright 2017 The Associated Press.