What if a dam breaks upstream from Eugene?

SPRINGFIELD, Ore. - A catastrophic dam failure in Lane County is unlikely - but not out of the question.

And the question is of keen interest in Lane County, home to 9 major dams.

The US Army Corps of Engineers shared dam failure inundation maps with the media and county and city emergency response officials.

Scott Clemans with the Army Corps said the maps show the results of a catastrophic dam failure, not a 100-year flood.

"We are talking in these maps about a worst-case scenario," Clemans said. "We're talking about a widespread and rapid dam failure."

He said there's a 1 in 10,000 chance per year of a catastrophic event - small odds with severe consequences.

For example, if Hills Creek Dam dam failed, Oakridge residents will have to act fast.

"About a 40 foot increase in about four hours," he said.

Closer to downtown Eugene, you'd have more time to react.

"Water would start to increase in about 9 hours and 15 minutes after the dam failed," Clemans said.

In 14 hours, the water could top out at 454 feet above sea level - about 42 feet above the streets of downtown Eugene.

There are a number of reason a dam could break, but the flooding that would follow is not necessarily affected by why the dams breaks.

The key factor would be how much water is in the reservoir above the dam. The innundation maps look at both high pool - a normal water level in the reservoir - and maximum, the scenario where there is a flood upstream of the dam and then the dam breaks

The maps are intended for emergency personnel and city officials, who need to be prepared for the unlikely event of a dam failure.

"If they know that in four hours the water level in Oakridge is going to rise 40 feet, who do they need to get out of the way? What routes are they going to take? Who needs to be notified?" Clemans said.

The Army Corps is hosting five closed-door meetings in Lane County in the next several weeks for public officials and and the over 500 residents who expressed interest in the maps to Lane County Emergency Management.