Evacuations ordered below Lake Oroville dam
February 12, 2017
• Emergency spillway may soon fail
• State announces it with a Tweet
• This story will be updated as developments occur
Water pours out of Lake Oroville via its emergency spillway in this Sunday morning photo by the Butte County sheriff's Office
Those living downstream of the Lake Oroville dam have been ordered to evacuate as the dam’s emergency spillway was in danger of failing, the state Department of Water resources said Sunday evening.
"Use of the auxiliary spillway has lead to severe erosion that could lead to failure the structure," says a DWR Tweet sent at about 5:10 p.m.
The Yuba County Office of Emergency Services ordered an evacuation for "all Yuba County on the valley floor."
Evacuation centers were opening in Butte and other counties.
But by 7:30 p.m. Sunday, enough water had been let out of the massive lake that emergency workers were beginning to breathe a bit easier.
Erosion of the emergency spillway was first spotted about 3 p.m. Sunday. Engineers said the hole was eroding at a “significant” rate, says Butte County Sheriff Kory Honea.
Kevin Lawson of CalFIRE says crews have been sent to the scene to assist if needed and CalFIRE helicopters have been put on reserve.
“We have monitors on the primary spillway and they have not detected migration” of the erosion, a spokesman for the DWR says.
Meanwhile thousands of people were evacuating, clogging Highway 70 toward Sacramento to the south.
"The next several hours will be crucial in determining whether the concrete structure at the head of the auxiliary spillway remains intact and prevents larger, uncontrolled flows," DWR said at 6:21 p.m.
The dam at Lake Oroville is the nation's tallest. The lake behind the dam is the second largest in California.
As water pours in from recent storms, the lake has filled to near capacity. The avoid overtopping the dam, the DWR had pressed into operation the never-before-used auxiliary spillway after heavy outflows from the normal spillway created a massive sinkhole in the spillway.
An uncontrolled flow of water from the lake could threaten low-lying areas of Oroville and, further downstream, the smaller city of Gridley.
At 6 p.m., the outflow was about 100,000 cubic feet per second. The Feather River has a technical capacity of 210,000 cubic feet per second. But while the river might have capacity, there is concern that if the amount being released suddenly spikes through a failure, then there could be extra pressure endangering them.
The dam is made out of compacted dirt. It was built by the Department of Water Resources and completed in 1968 as a key to the State Water Project.
The water released from the lake flows into the Feather River and from there into the Sacramento River, the state's largest river. It, in turns, empties into the California Delta, also known as the Sacramento-San Joaquin Delta, south of Sacramento and immediately west of Stockton