See the damage evolve: Oroville spillway erosion over time
Oroville Dam operators plan to halt water releases from the dam’s battered spillway Monday in order to ramp up efforts to remove a debris pile that’s preventing them from restarting a hydroelectric plant.
It will mark the first time since Feb. 7, when a giant crater opened in the concrete spillway, that no water has been released from Lake Oroville.
The state Department of Water Resources announced Sunday that with water levels at Lake Oroville reduced to 842 feet, and inflows at a modest 25,000 cubic feet per second, dam operators are confident that shutting off the outflows from the spillway makes sense.
The spillway has been releasing water the past few days at 50,000 cfs. DWR said it will begin dialing back the flows at 6:45 a.m. Monday, bringing the releases to a halt by sometime in the afternoon. DWR said it plans to keep the outflows at zero “for several days.”
Dam operators have been moving in equipment to a water channel beneath the spillway in order to remove the pile of mud, concrete and other debris that’s accumulated since the crater developed Feb. 7. The pile is backing water up into the dam’s hydro plant, making it impossible to restart.
When operational, the hydro plant can release water at 14,000 cfs, “which will allow DWR to better manage reservoir levels through the remaining spring runoff season,” the agency said.
Dam operators shut off the spillway for about a day after the crater was spotted. They resumed outflows, but as a giant storm swelled lake levels, water flowed over the emergency spillway on Feb. 11 for the first time in the reservoir’s 48-year history. A day later, after severe erosion was spotted on the unlined hillside and dam operators feared the emergency spillway would fail, 188,000 downstream residents were evacuated.
By accelerating flows from the damaged main spillway, DWR was able to reduce lake levels, halt the flows over the emergency spillway and arrest the erosion. Since then the lake has fallen to 842 feet – 59 feet below the top of the emergency spillway.