Oroville Dam Crisis Foreseen Over 11 Years Ago
A hasty, chaotic evacuation of 188,000 people occurred in Northern California on Sunday, Feb. 12 after officials warned of serious erosion in a hillside due to the use of an auxiliary or emergency spillway of the over-capacity Oroville Dam in Butte County. The decision to use the emergency spillway was made after engineers discovered that "a 200-foot-long, 30-foot deep hole" developed in the main, concrete-lined spillway.
"The water began eating away at the ground beneath the top of the auxiliary spillway, carving deep gullies into the earth," reports Brad Plumer for Vox.. "On Sunday afternoon, the [state] Department of Water Resources warned that the lip of the auxiliary spillway, which was never built to be as sturdy as the main spillway, was in danger of 'failure' if the ground beneath gave way."
However, the potential collapse of the hillside [see video from drone] that prompted the sudden evacuation orders should not have come as a surprise. Three groups had foreseen it, but they were rebuffed by a federal commission after DWR complained about the cost to address the problem.
Just to clarify, it was not the dam that was under threat of collapse, but flooding due to collapse of the auxiliary spillway.
Three environmental groups — the Friends of the River, the Sierra Club and the South Yuba [River] Citizens League — filed a motion with the federal government on Oct. 17, 2005, as part of Oroville Dam’s relicensing process, urging federal officials to require that the dam’s emergency spillway be armored with concrete, rather than remain as an earthen hillside.
The groups filed the motion with FERC, the Federal Energy Regulatory Commission. They said that the dam, built and owned by the state of California, and finished in 1968, did not meet modern safety standards because in the event of extreme rain and flooding, fast-rising water would overwhelm the main concrete spillway, then flow down the emergency spillway, and that could cause heavy erosion that would create flooding for communities downstream, but also could cause a failure, known as “loss of crest control.”
FERC rejected that request, however, after the state Department of Water Resources, and the water agencies that would likely have had to pay the bill for the upgrades, said they were unnecessary.
On Tuesday (Feb. 14) afternoon, the evacuation order had been lifted, changed to an "evacuation warning", report Veronica Rocha and Paige St. John for the Los Angeles Times.
"We have concluded it is safe to reduce the emergency evacuation order to an evacuation warning," said Butte County Sheriff Kory Honea, who had made the initial call Sunday to evacuate a large swath of three counties below the imperiled dam.
At the time, residents were told the spillway to the dam could collapse within an hour.
Hat tip to Mike Painter.