More than five weeks after erosion damage at Lake Oroville forced residents to flee to high ground, the Butte County Sheriff's Office on Wednesday announced it had lifted an evacuation advisory.
More than 100,000 Butte County residents were given an hour's notice to evacuate on Feb. 12, when officials feared that a concrete weir on the reservoir could collapse and send a 30-foot wall of water into the valley below. The order took residents by surprise because Department of Water Resources officials had repeatedly assured them that erosion damage to the reservoir's main and emergency spillways posed no threat.
Although the mandatory evacuation lasted just days, residents had been living under an evacuation advisory until Wednesday. They had been told to remain alert and prepare to leave at a moment's notice while crews worked around the clock to repair erosion damage.
"I feel satisfied with the progress made in reinforcing the primary spillway, emergency spillway and returning the Hyatt Powerhouse to an operational state, as well as the successful efforts by the California Department of Water Resources to lower the lake level enough to buffer for future storms," Butte County Sheriff Kory Honea said in a statement.
Meanwhile, in a report first obtained by the Associated Press, a team of experts warned of a "very significant risk" if the Oroville Dam's main spillway is not operational again by the next rainy season.
The warning was contained in a report made by a federally created investigative team for the Oroville Dam.
It says repair crews at the dam have only a few months to make sure the spillway is in good enough shape for the next rainy season, which starts in November.
The report does not specify the risk but notes that it is "absolutely imperative" that the emergency spillway not be used. The emergency spillway's use last month began the cascading set of problems that are still being addressed.
State water officials are continuing to drain the reservoir — the second largest in the state — to make room for runoff from melting snowpack in the Sierra Nevada.
There is enough water frozen in the mountains above Oroville to fill the reservoir more than once over, according to official estimates.
DWR officials responded to the federal investigative team's report late Wednesday afternoon.
"As we have stated from the beginning, DWR's objective is to have a fully functional spillway before the start of the next storm season," the agency said. "With the support of the governor's executive order in February, we are expediting response and recovery efforts, and we'll be working 'round the clock through spring, summer and fall to make that happen."
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6:55 p.m.: This story was updated with a response from DWR to the investigative report.
2:40 p.m.: This story was updated with information on the federal investigating team's warning about the risk if the dam's main spillway is not operational again by the next rainy season.