Regulators at the time recommended that state officials implement more public-warning systems, carry out annual public education campaigns and work to improve early detection of any problems at the dam.
Six years later, state and local officials have adopted some of the recommendations, including automated warnings via reverse 911 calls to residents. But local officials say the state hasn't tackled some other steps that could improve residents' response, such as providing routine community briefings and improving escape routes.
The catastrophic scenario of a sudden breach at California's second-largest water reservoir, outlined between 2010 and 2012 in online archives of federal dam regulators, is a different and far graver situation than the concern that prompted sudden evacuation orders Sunday for 188,000 downstream residents.
Operators of the nearly half-century-old dam in California's Sierra Nevada foothills became worried that the water cascading from the reservoir after a series of winter storms could roar uncontrolled down a rapidly eroding emergency spillway toward towns downstream.
The shortfalls in organization as well as infrastructure to quickly get residents out were on full display in the chaotic hours after the evacuation order. Residents found themselves caught in traffic jams for hours on clogged roads, leading some families to abandon their cars. While many local officials and ordinary people rushed to help direct traffic and staff emergency shelters, evacuees also reported seeing fistfights on gridlocked roads.
In an email Thursday, state water agency spokesman Ed Wilson said that despite the repeated back-and-forth correspondence between state and federal officials about reducing detection and response times in a sudden dam failure, the scenario was "hypothetical" and "not how dams typically fail in real life."
Local officials, residents and a Florida-based evacuation expert said the federal-state discussion highlights the steps that the state Department of Water Resources and others still should take to improve warning and escape for people downstream.
"You know what the evacuation plan is? 'Get the hell out of town!'" said Kevin Zeitler, a critic of the state water agency's interactions with communities downstream of the dam. The state informed federal dam regulators that local emergency officials "do not believe there is enough time to perform evacuations in the communities immediately downstream of the dam during a sudden failure," according to a Feb. 8, 2011, letter reviewed by The Associated Press.
Absent "significant" advance warning, emergency responders instead would likely withdraw to safer ground and prepare for victims, said the same letter by the Federal Energy Regulatory Commission, which oversees safety of hydroelectric dams, in a summary of the state's conclusions.
The federal government in recent years has made evacuation and emergency-response plans for major dams off-limit information for the public, for fear details could be exploited for terror attacks or hacking. California officials cited that reason this week in declining to release the latest emergency plans for the dam.
Wilson, the state water agency spokesman, said authorities have implemented the reverse-911 automated warnings recommended by federal regulators, and also activated an emergency broadcast system locally. Residents confirmed the reverse-911 system worked Sunday.
With months left in the rainy season, state spokesperson Nancy Vogel said California now has drones, cameras and human lookouts watching the dam and its spillways. Operators have been releasing torrents of water down the damaged main spillway to avoid a repeat of last weekend.
Even with round-the-clock efforts by dam operators, Oroville Mayor Linda Dahlmeier immediately began praying for those closer to the dam when she heard the first drops of rain hit the metal roof of her home Thursday.
"You just start bawling," Dahlmeier said. "This is Mother Nature's hand." Oroville used to have civil-defense sirens for emergencies, Dahlmeier said, but funds for such public expenses have dwindled in the Sierra Nevada foothill counties. Neither she nor others recalled the annual safety briefings for the public that federal regulators urged of the state water agency.
A May 2013 hazards-assessment report by Butte County estimates 8,735 people live in a so-called inundation zone in Oroville that would likely be under water in the event of a sudden rupture at the dam, which is five miles from the vulnerable area in Oroville.
Since the 1990s, Oroville and other communities in Butte County have asked the state for the $300 million it would take to widen the full route of a key highway out of the county from two lanes to four, said Jon Clark, head of the Butte County Association of Governments.
Unquestionably, that would have helped in the evacuations, Clark and others said. For Butte County's many low-income retirees and others unable to drive, Clark's association got buses on the road Sunday to carry people to safety.
In a disaster as sudden as a major problem with a dam, authorities will have had warning signs telling them to increase their vigilance, even if that is just forecasts of storms coming, said John Renne, an urban-planning professor at Florida Atlantic University.
And the public can almost always be warned, even if it entails greater government investment in public-warning technology. "Minutes can save lives," Renne said.
Associated Press writers Don Thompson in Sacramento and Tim Reiterman in San Francisco contributed to this report.