Oroville Dam shuts down main spillway, crews begin damage assessment
After flows down Oroville Dam’s fractured main spillway were dialed back to nothing Monday afternoon, heavy equipment operators worked through the night to clear the massive debris pile that has formed at the base of the damaged concrete structure.
The efforts to open the channel below the spillway, which will allow engineers to once again fire up the dam’s hydroelectric plant, appear to be paying off, said Nancy Vogel, a spokeswoman for the California Natural Resources Agency.
The water in the channel below the spillway dropped 23 feet in less than a day, which should be enough to get at least one of the turbines up and running, perhaps as early as Thursday. Electrical crews are working to get transmission lines from the power plant reattached to the grid, Vogel said.
The massive mound of concrete, rubble and debris that has formed at the base of the crumbled spillway raised channel levels to the point that the hydroelectric plant can’t function. The plant is the dam’s primary outlet outside of the rainy season.
The power plant, when fully operational, can release about 14,000 cubic feet per second. While just a fraction of what the spillway can release, outflows from the plant would be enough to handle about half of the inflow expected as the Sierra snowpack begins melting into the reservoir in the next few weeks.
With the spillway closed, the reservoir level rose about two feet overnight, to 840 feet, or 61 feet below the top. To maintain flood safety, state officials said they’ll open the spillway gates again before the lake rises above 860 feet. With the spillway shut down, engineers also will get a chance to inspect the broken span, as well as the canyons that have formed in adjacent hillsides after a hole broke open in the chute on Feb. 7.