OR computer simulator helps tsunami planning

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by NANCY MCCARTHY, The Daily Astorian

kgw.com

Posted on June 8, 2011 at 12:02 PM

Updated Wednesday, Jun 8 at 12:42 PM

CANNON BEACH, Ore. -- With just a click on the computerized map of Cannon Beach, the numbers start rolling. Seconds fly by, then minutes.

More numbers roll over so fast they can barely be read, but the white-lettered labels next to them remain still: "Dead," "Safe," "Evac," "Wait."

The ocean begins to sweep over the lines that indicate streets. Ecola Creek bulges blue. Yellow crosses denote refuge areas. Red squares suddenly flash, then disappear.

These scarlet blips on the map show where people will run as a tsunami nips at their heels and where they may fall.

By 1:57:50 on the map, there are 939 dead, 6,846 safe, 0 Evac and 0 Wait. That could be the result if an evacuation building were placed on the site where the current City Hall stands. Produced by Oregon State University Professor Harry Yeh and computer technologist Jonathan Karon, six computerized simulations show where people might go when the Cascadia subduction earthquake and tsunami hit Cannon Beach.

The simulations accompany a 13-page report that compares the effects that a proposed tsunami evacuation building might have at two different sites, as well as a new bridge over Ecola Creek. The study can be found at http://net junky.com/cannon-beach/ In each scenario, the numbers of people saved and the possible fatalities are calculated.

The results: An evacuation building placed at Spruce and Washington streets would be more effective than a building proposed on Gower Street where the current City Hall stands.

The Washington Street building could reduce fatalities by 65 percent, while fatalities at the Gower site might be reduced by just 11 percent overall, according to the computer simulations. If a new bridge over Ecola Creek were constructed, how many lives would that save? Close to 400, according to the calculations in the study.

Already the study has forced city officials to rethink the idea of investing any money for an evacuation building at the current City Hall site on Gower Street.

"We aren't funding any more studies at the City Hall site," said Mayor Mike Morgan. "It is possible we could look at another location, possibly at Spruce and Washington, adjacent to the cell towers."

However, the city will spend $10,000 to study four bridge designs to determine what type of bridge would withstand an earthquake and tsunami, said City Manager Rich Mays. Depending on the design chosen and the cost, the bridge may be built for pedestrian use only, or the current Ecola Creek Bridge could be replaced.

If anything, the study shows that "doing something helps," said Jay Raskin, former mayor and architect, who originally proposed the Gower Street evacuation building.

"If we just have to rely on evacuation without help, it won't save as many lives," Raskin said. "Building a bridge would help; doing something else will help."

Yeh is an expert in ocean waves and tsunami hazards who has worked closely with Cannon Beach city officials as they study the possibility of constructing the nation's first evacuation building to house people during a tsunami. He and Karon tracked the effects of six potential scenarios, using data from previous studies and from the city.

The calculations are based on the potential population for a summer day. The researchers "placed" three people in each of 2,455 tax lots, plus 106 people at the Cannon Beach Elementary School, 121 at the Cannon Beach Christian Conference Center and 293 on the beach and in city parks. The total: 7,885 people, nearly five times the city's year-round population of 1,690.

This is the scene: It is the middle of the day. People are playing at the beach, working in their stores, puttering around the house. Suddenly, the ground begins to shake, maybe even sink under their feet: The Cascadia earthquake 50 miles offshore has begun. For three minutes the earth shakes. Finally, it ends, and people begin to stand up. As they understand what is happening, they begin to run for higher land.

The study estimates 80 percent will understand that a tsunami will occur almost immediately, and they begin running toward higher land. Every minute after that at least 15 percent more will begin evacuating.

In the first 17 minutes, from the earthquake until the tsunami surges on the beach, an estimated 180 deaths will occur, from the earthquake and from those at the water's edge who are unable to reach higher ground as the first water hits land.

At 18 minutes, the water is onshore and moving rapidly. If an evacuation building were at Gower and an earthquake/tsunami-proof bridge were over Ecola Creek, more people would find safety at the evacuation building for the next five minutes. "After that," the study says, "the bridge's impact on survival rates surpasses that of the Gower" evacuation building.

But, the study notes, for people to cross the bridge to reach higher ground on the north side of Cannon Beach, it must be elevated. The tsunami will arrive "very soon" after the earthquake and the south bank of Ecola Creek could sink significantly. "If the bridge is not sufficiently raised, it is covered by a tsunami while evacuees are on it," the study says.

The researchers looked at six scenarios involving the existence of tsunami evacuation buildings and bridges as well as the lack of safety structures.

The survival rate is higher in the scenario where the bridge is replaced than in the scenario where there is a combination of the Gower Street evacuation building and the bridge, the study says. People downtown would be lured to the evacuation building instead of the bridge, leaving them in the "vulnerable lowlands" longer, according to the researchers.

Although the 1,761 people going to the Gower Street building is only 5 percent smaller than the 1,818 going to the Washington Street evacuation building, the survival rate is almost 500 percent more at the Washington Street building.

This is because the Gower Street building could divert those who might otherwise go to Sunset Hill and fail to reach the building in time. Also, those in downtown Cannon Beach north of Washington Street would reach higher ground faster on their way to the Washington Street evacuation building.

According to the simulations, 48 people could be trying to enter the evacuation building every 10 seconds and could create serious congestion at the building's entrance.

At least 241 people could be on the bridge at one time, the study says. A floating or suspended footbridge "likely would not accommodate all of the evacuees and might create a dangerous bottleneck during evacuation," it says.

The study shows nine "refuge" sites indicating the nearest high ground where people probably would seek safety.

The researchers used a typical walking speed of 88 meters per minute; they calculated how many people would reach each site in each of the six scenarios, and how many might die trying to get there.

Morgan said he was pleased that the City Council commissioned the $25,000 study.

"I'm glad we're focusing on evacuation rather than structures," Morgan said. "Evacuation is the key to survival. I think people are increasingly focused on getting to high ground."

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