Arcata braces for rising seas

Kevin L. Hoover
Mad River Union

ARCATA – With the Humboldt Bay and the Pacific Ocean lapping thirstily at its southern edges, Arcata’s low-lying lands are facing eventual inundation. It likely won’t happen overnight, and property in the area may still see use, and even fresh construction, for decades to come.

But preparing for the inevitable, with all its uncertainties, is a mission Arcata can’t avoid, and it’s using projections and planning horizons that stretch far into the future – even to the year 2100.

The Arcata City Council and Planning Commission met April 30 to confer and coordinate the city’s sea level rise plans and policies. Arcata Community Development Director David Loya projected an aerial photo of a 1960s-era flood along the bay which showed submerged roads and buildings, noting that someday, when the sea has risen as it is projected to do, such views will reflect daily tidal activity.

Accommodating the incoming waters will require all kinds of policy modifications to the Land Use Code, general Plan and Local Coastal Plan. But complicating planning is the uncertainty about the rate the water will rise.

The city is using a number of models looking out to 2100, though science is providing new projects almost daily.

The strategy boils down to three steps – protect, accommodate, retreat. That is, protect with levees those area where water can be held back, particularly critical facilities such as the Wastewater Treatment Plant. That will require significant investment. Accommodate with limited adaptation for features that can’t be defended or relocated. And finally, where defenses aren’t feasible or affordable, retreat to higher ground inland.

One estimate holds that a $15 million system of 18-foot eco-levees and sea walls will preserve much of south Arcata. That would protect public and private assets conservatively valued at $141 million. “The question mark is, for how long?” Loya said.

An integrated strategy is needed, and that will include regulations on development. Property owners may still invest in coastally located facilities, but they’ll have to factor in added expense for protection while looking realistically at how long those areas will be habitable and usable.

Developers in those areas may have to sign conditions of approval for their projects which acknowledge the inevitability of eventual abandonment.

Those who live, work or own property in initial inundation areas such as south Arcata, Sunny Brae, the Arcata Bottom and the low-lying Bloomfield neighborhood (elevation 13 feet) will be hit first, but all of Arcata will be impacted since the town’s sewage treatment is located along the bay.

“It doesn’t matter where you are in the city. If you flush your toilet, and I suspect many of you do, it’s coming down here,” Loya said, pointing to the sewage plant. “And so it’s everyone’s problem. It’s not whether, but where we’re going to protect. Let’s come up with an integrated strategy.”

Preparing for sea level rise pushes the planning horizon to the year 2100, straining planners and projections far beyond what is normally considered. Among the unknowns that will affect the rate of water rise is how well greenhouse gas emissions are controlled – a huge unknown.

As with variables, models abound. If, worst case, the ice caps melt and Greenland’s ice sheet slides into the ocean, all of Arcata will be underwater. If by 2040, the sea has risen by half a meter, Loya said, all bets are off. “We’re in crisis mode,” he said. “We’re going to be in emergency management mode, not planning mode.”

More likely, and given 95 percent probability, is a gradual but significant rise of .8 meters by 2040. The higher nominal water levels will make King Tides and 500-year storms and  make inevitable flooding along South G Street several times per year.

Quite a bit of the shoreline is imperiled, but with permanent flooding along parts of the Arcata Bottom, new shoreline habitat would also be created and can be planned for. “We want to start thinking about targeting areas for habitat restoration,” Loya said.

Coordination with the Coastal Commission has been problematic even during normal planning scenarios, but Loya said efforts at communication has been stepped up. “We’ve been handing documents back and forth for two years now,” he said. “We’re making progress.”

Loya said that the measures and mitigations required to combat the effects of sea level rise are far beyond Arcata’s means, and will require Arcata to compete for financial aid from state and federal sources.

Planning Commissioner Melanie McCavour said that Arcata’s efforts could stand out statewide – and make Arcata more competitive for funding – in a couple of ways. One is by pursuing wetlands restoration in the newly created coastal areas.

She also pointed out that low-income residents are likely to be hit hardest, at least initially, by sea level rise. This because they inhabit areas of Arcata in most immediate peril, such as South G Street and Marsh District. “Most of the coastal communities are very affluent. We have a lot of people of color and of lower income living in our coastal area,” she said.

Loya agreed, noting that those fleeing climate change elsewhere could settle in Arcata, causing gentrification and marginalization of the poor, which inclusion of a strong social justice policy could address.

Other underconsidered consequences of sea level rise include the release of toxic material presently buried underground in areas set for inundation.













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