California town builds 'tsunami-resistant' port

Crescent City on the US west coast suffers badly from big waves generated by earthquakes

PUBLISHED : Saturday, 24 November, 2012, 12:00am
UPDATED : Saturday, 24 November, 2012, 3:14am

It does not matter if the earth sways in Chile, Alaska or Japan, the formation of the sea floor along the US west coast generally aims any tsunami surges at the tiny California port town of Crescent City.

Churning water rushes into the boat basin and then rushes out, lifting docks off their pilings, tearing boats loose and leaving the city's main economic engine looking as if it has been bombed.

That's what happened in March last year, when a Japanese earthquake sparked a tsunami that tore across the Pacific before reaching Crescent City, where it sank 11 boats, damaged 47 others and destroyed two-thirds of the harbour's docks.

Port officials are hoping that tsunami will turn out to be the last to cause such havoc for the tiny commercial fishing village on California's rugged northern coast. Officials are spending US$54 million to build the US west coast's first harbour able to withstand the kind of tsunami expected to hit once every 50 years - the same kind that hit last year, when the highest surge in the boat basin measured 2.5 metres and currents were estimated at 6.7 metres per second.

Officials are building 244 new steel pilings that will be 75cm in diameter and 21 metres long. They will be sunk nine metres deep into bedrock. The pilings will extend 5.5 metres above the water so that surges 2.3 metres up and down will not rip docks loose. Crescent City was not the only west coast port slammed by the tsunami, which was generated by a magnitude-9 earthquake in Japan.

The waves ripped apart docks and sank boats in Santa Cruz, California, and did similar damage in Brookings, Oregon, just north of Crescent City. But their geographical location doesn't make them as vulnerable to multiple tsunami.

"Normally, Crescent City takes the hit for all of us," said Brookings harbour master Ted Fitzgerald.

Since a tidal gauge was installed in the boat basin in 1934, the small port has been hit by 34 tsunami, large and small. It typically suffers the most damage and the highest waves on the west coast, said Lori Dengler, professor of geology at Humboldt State University.

The sea floor funnels surges into the mouth of Crescent City's harbour, and the harbour's configuration magnifies them, experts say.

A wave generated by an earthquake in Alaska on Good Friday, 1964, killed 11 people and wiped out 29 city blocks. That was 10 years before the boat basin was even built.

When the waves hit last year, the port was still repairing damage from a tsunami that hit in 2006. Officials already had a plan for dealing with future tsunami, said Ward Stover, owner of Stover Engineering in Crescent City, which put together the plan.

With no tsunami building codes, Stover said the state of California and Crescent City decided to prepare for the kind of tsunami expected to hit every 50 years.

They rejected as too expensive building a tidal gate to close off the mouth of the harbour or trying to survive a powerful tsunami like the one that hit in 1964. Instead, they planned to make the docks strong enough to ride out the most likely surges.

"It's tsunami-resistant, not tsunami-proof," Stover said.