An earthquake rattles the Willamette Valley. The shaking breaks loose the 114 billion gallons of water normally stored behind the Hills Creek Dam southeast of Oakridge.

The water rushes down the Highway 58 corridor. It swamps downtown Oakridge in about 67 minutes.

Unabated, the force of the water overwhelms the Lookout Point and Dexter dams. Nine hours after Hill Creek's failure, floodwaters arrive in the Eugene-Springfield metropolitan area. At the waters' peak five hours later, parts of the University of Oregon campus are under about 17 feet of water.

More than 100 Eugene residents will find out tonight whether their homes are in this path of destruction.

The U.S. Army Corps of Engineers is letting about 300 residents view updated maps that show what could happen if any of the agency's nine dams in Lane County suffered a catastrophic failure.

The first of the four viewing sessions was in Westfir on Tuesday.

The final two viewings for residents to view and learn more about the maps are next month in Springfield and Cottage Grove.

Corps officials stress that the possibility of a dam failure is remote. They explain that the maps are tools that local emergency managers can use to draft plans to respond in the highly unlikely event of a dam failure.

But public interest in seeing the maps is high after The Register-Guard reported that the corps had updated them.

The viewing sessions are not open to members of the public who show up without an invitation; the corps arranged the viewings only for residents who had asked to see the maps. The corps may schedule future public viewing sessions.

Corps officials also say they will not release the maps publicly because of federal security requirements, the maps' complexity and their one-sidedness.

"When we're having a conversation with the public about risk, we don't just want to tell them the risk," said Scott Clemans, spokesman for the corps' Portland District, during a media briefing in downtown Eugene on Tuesday. "We want to tell them what do you do about this risk, what is it you need to take action on. What is it you need to know. ... And you can't do that by just handing them this map."

The Portland district is among the first in the nation to receive the updated maps.

It distributed them to local emergency managers last year.

It's the first time the corps has updated the maps in more than 30 years.

Advancements in technology have allowed the corps to develop more detailed and accurate modeling and maps, said Matthew Craig, the Portland district's dam safety program manager.

The maps pinpoint the areas that would be flooded, the water level at the start and peak of the flooding, and how long it would take for the flooding to start and reach its maximum height after a dam failed.

They also identify schools, hospitals and police and fire stations.

The maps identify the flooded areas based on two scenarios: a "sunny day failure" when both the reservoir level and the flow in and out of it is normal, and a worst-case scenario with an extremely high reservoir level and water flows.

There are maps for failures of each of the nine dams, which were built between the 1940s and 1960s: Blue River, Cottage Grove, Cougar, Dexter, Dorena, Fall Creek, Fern Ridge, Hills Creek and Lookout Point.

Corps officials caution that while the maps detail the consequences of a dam failure, they are silent on how it occurred, such as by a quake, massive storm or terrorism, or the likelihood of it occurring.

To illustrate the latter, Craig provided two statistics during the media briefing.

Craig said on average there is a 1 in 10,000 chance that a dam more than five years old will fail in a given year.

That's the same odds of a U.S. resident between the ages of 10 and 18 dying in a given year, Craig explained, with higher odds for adults.

"The dam is not contributing any sort of significant risk to an individual, even if they live downstream of a dam," he said.

Since 2000, the U.S. Bureau of Reclamation reported two dam failures that resulted in at least one death.

The most recent occurred in 2006, when an earthen dam on the Hawaii island of Kauai failed during heavy rains, killing seven people.

The U.S. Department of Homeland Security cited the bureau's data in a September 2011 report.

Lane County Emergency Manager Linda Cook said the detail in the updated maps has allowed her department for the first time to identify routes to get people to high ground.

The evacuation routes are in draft form, and Cook is working to get commitments from agencies that they would direct motorists to those routes in an emergency, before they are released publicly. The routes also could be used in a less catastrophic event, such as a major flood, she said.

"This is not going to be ready for prime time anytime soon," she said. "I'd say we're at least 12 to 18 months out."

Clemans said one reason the maps aren't made public is because the data used to create them is considered sensitive and is protected under Homeland Security regulations.

A decade-old lawsuit shed some light on the corps' concern about releasing the maps.

In 2002, an environmental group sued the U.S. Bureau of Reclamation after the agency denied its request for inundation maps that it prepared for the Hoover and Glen Canyon dams. A federal judge dismissed the lawsuit.

Larry Todd, who served as the federal agency's chief of security at the time, submitted a written statement that releasing the maps would give terrorists information about the amount of damage that could be inflicted on communities by destroying a dam.

"Because the inundation maps show flood travel times and water depths, terrorists could use the inundation maps to help plan and execute sequenced attacks, which could include attacks on bridges and roads to cut off evacuation routes or attacks on communications facilities to disrupt emergency response," he said.

Follow Christian on Twitter @RGchill. Email

Recommended for you

(0) comments

Welcome to the discussion.

Keep it Clean. Please avoid obscene, vulgar, lewd, racist or sexually-oriented language.
Don't Threaten. Threats of harming another person will not be tolerated.
Be Truthful. Don't knowingly lie about anyone or anything.
Be Nice. No racism, sexism or any sort of -ism that is degrading to another person.
Be Proactive. Use the 'Report' link on each comment to let us know of abusive posts.
Share with Us. We'd love to hear eyewitness accounts, the history behind an article.