CANNON BEACH — Cannon Beach could be the subject of another tsunami study, but this time, the study won’t be so much about the surge of water but what's in the water.

“The tsunami's impacts are affected by the area's surroundings,” said Harry Yeh, professor of civil and construction engineering at Oregon State University. He spoke during a city emergency preparedness committee meeting Friday.

Yeh, who is an expert in the hydrodynamics of tsunamis, has conducted previous tsunami studies, using Cannon Beach as the subject. This time, he is seeking an Oregon Sea Grant from OSU to study what kind and how much debris might be generated by a tsunami.

The accumulation of debris could impact the amount of time it takes for emergency responders to arrive, and it could delay the town's recovery, Yeh said.

Because the Japanese and North Oregon coastlines are similar, Yeh said the potential effects of a tsunami in Oregon could be similar to those experienced by Japan in 2011.

Yeh provided the committee a short film showing the water rushing into a town in Japan. The streets became clogged with debris from buildings the waves had already swept away, and that debris, in turn, caused other buildings to collapse.

“Thirty hours after the event, the debris was blocking the roads, causing a delay in the rapid rescue and relief mission,” Yeh said.

“Debris piled on high on the roadway is not something people think of,” he added.

In Japan, the combination of debris and leaking oil also caused fires, Yeh said.

Ships couldn't reach the towns because debris blocked the ports and harbors, he said.

Although Cannon Beach doesn't have much driftwood to be swept into town, it does have many wood-framed buildings and vehicles, Yeh noted.

The buildings probably would withstand an offshore, Cascadia earthquake, but they would go down in a tsunami surge, he said.

In Japan, where debris accumulated nearly everywhere, “recovery has been very complex,” he added.

Yeh also told the emergency committee that the U.S. Highway 101 bridge on the north side of Cannon Beach was “critical” for reaching higher land.

“If it is washed away, there would be very difficult access south of Cannon Beach and to all of the Oregon coast. Somehow you have to make access to the Willamette Valley,” he said.

The Fir Street Bridge over Ecola Creek also is important, Yeh said. “That small bridge has to be standing after the ground shakes, but it can be washed away in the tsunami.”

Tsunami experts estimate it will be 15 to 20 minutes after the earthquake before a tsunami hits shore, allowing some pedestrians to cross the bridge before it is washed away. However, because the current bridge is also expected to collapse in an earthquake, city officials have debated for at least two years about whether a pedestrian bridge, estimated to cost at least $800,000, should be built.

The 1964 tsunami, which occurred following an earthquake in Alaska, knocked the bridge over Ecola Creek 125 upstream and required traffic to use the roads south of downtown to reach the highway.

Les Wierson, a member of the emergency preparedness committee, said he worried about debris in a “big” earthquake and tsunami. Committee member Doug Wood also said he was concerned that the Arch Cape tunnel on U.S. Highway 101 and the Edwards tunnel on U.S. Highway 26 would collapse in an earthquake, cutting off access to Portland for several weeks or months. Those highways also have bridges all along the routes that could fall, he said.

Yeh agreed with their concerns.

“Each community is going to be on its own,” he said.


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