Submitted

Tsunami-resistant renovation was already in the works, but after 2011 surges wrecked harbor, new federal money lowered the local burden by millions

In March 2011, Crescent City Harbor was destroyed by the Tohoku tsunami, tearing docks from pilings, sinking 11 boats and dumping more than 100,000 cubic yards of silt and other fine material into the inner boat basin. But the port most likely would have endured the entire calamity with only minor damage if the tsunami had come knocking a couple years later.

On Feb. 18, 2011, the Crescent City Harbor District was handed a permit from the California Coastal Commission greenlighting reconstruction of the inner boat basin to withstand a 50-year tsunami - a force greater than what struck in 2011. The harbor was severely damaged by a tsunami in 2006, and for years harbor staff had been lobbying state agencies to fund a port designed to withstand the type of tsunami expected once every 50 years instead of simply rebuilding what was destroyed.

The California Office of Emergency Services, at the time known as Cal Emergency Management Agency, was on the hook to pay 75 percent of the repair costs from the 2006 tsunami and balked at the cost of funding a 50-year tsunami-resistant port instead of replacing the original design. The project pitched by harbor staff would be one of the largest ever taken on by the state without federal funding, prompting state officials to drag their feet on the project.

The Coastal Commission originally requested the project be designed for a 100-year tsunami, but since that would have required a 6-foot wall around the harbor, the commission was convinced by the harbor's logic that a 50-year, or 15-foot wave, design would be more cost effective in the long term and permitted that option.

Less than a month after the Coastal Commission awarded the permit, the wisdom of a 50-year design was proven by the Tohoku tsunami. The harbor's hired engineers had modelled impacts predicted from a large tsunami and those models were proven to be dead-on from the March 2011 tsunami.

If the California Emergency Management Agency had its druthers, the port likely would have been rebuilt much faster and to the same capacity as it was in 2006 - only to be devastated again by the 2011 tsunami. The cost concerns of Cal-EMA were also wiped away by the 2011 tsunami as the event was declared a federal disaster, authorizing federal funds, and decreasing the state's contribution from 75 percent to 18 percent.

Not only did the state have to foot less of the bill for the tsunami-resistant port, but Crescent City Harbor's own cost contribution was also greatly reduced with the feds' involvement, from 25 percent of cost to 6.25 percent of the $34 million inner boat basin reconstruction project. Due to the damage inflicted in 2011, another $20 million was spent on repairs to the outer boat basin.

Scott Feller, secretary for the Harbor District, said since the 2006 event started the environmental and permitting process, the port was able to rebuild very quickly after the 2011 tsunami.

"We were already on our way and that allowed us to move a lot faster," Feller said.

A first for the West Coast - maybe the world

As the tsunami capital of the continental U.S., many feel Crescent City deserves to be at the forefront of tsunami engineering, and the reconstructed boat basin is just that.

Completed in 2014, Crescent City Harbor became the first tsunami-resistant port on the West Coast and quite possibly on the planet.

What makes the port tsunami-resistant goes back to modelling that studied where a tsunami has the biggest impacts on the port.

The inner boat basin's layout funnels water through a narrow entrance, making the force of a tsunami a concentrated surge that hammers the first dock in its path. That dock, H Dock, has been designed to absorb this force and transfer it to the ground.

H Dock is a massive floating concrete wall, hanging seven feet down from the water's surface and is 16 feet wide.All of the steel pilings of the new inner boat basin are extra strong at 30 inches wide, and on the section of H Dock predicted to take the brunt of tsunami impact, the pilings are only an arm's length apart in order to fully absorb and transfer tsunami energy to the ground.Piling hoops that attach docks to the pilings weigh 600 pounds each, aiding in that energy transfer. Each 39-foot dock section of the 400-foot long H Dock weighs nearly 160,000 pounds. This wave attenuator, or "wave stopper" as dubbed by some harbor officials, is expected to transfer the tsunami force before it reaches any boats or other docks in the basin.

But the overall burly nature of the pilings, piling hoops and docks even apart from H dock, is what makes Crescent City Harbor tsunami-resistant.

The port has yet to endure a true tsunami to test its new facilities, but being in Tsunami City, USA, the next opportunity can't be too far away.

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