Arcata will protect, accommodate and retreat from rising sea waters

As the climate changes and Arcata Bay waters rise, Arcata faces fateful choices about its future; City Council to make far-reaching, costly decisions that will affect property values, development and shape Arcata well into the future; critical facilities to be protected, then relocated; policies forming up as massive public outreach and education required 

Here comes the water – and the protections against it. City of Arcata graphic

Kevin L. Hoover
Mad River Union

ARCATA – As climate change accelerates, the City of Arcata and its inhabitants face a near-stupefying range of uncertainties, some grave decisions and one brutal reality: the oceans are rising and will one day inundate low-lying Arcata.

The City Council reviewed its options at a Feb. 6 study session, putting details to an overall strategy. Arcata will protect what it can while it can, accommodate the encroaching waters where necessary and eventually, retreat – pull back to higher ground when the rising sea level makes alternatives unavoidable.

The most valuable and immediately vulnerable city asset is its $100 million Wastewater Treatment Facility, located on the edge of Arcata Bay. A long-planned, $40 million modernization upgrade is underway, and with few alternatives, adaptation – fortifying levees to enclose it – seems like the best way to wring more decades of use from the complex.

Costs depend on how extensive the armoring must be, which is keyed to the rate of sea level rise. But projections for how much higher the water level will be by the year 2100 vary wildly – from as little as several inches to more than six feet. Initially, the city is splitting the difference and using a more moderate projection of a .9 foot rise by 2030, 1.1 feet by 2050 and 3.2 feet by 2100.

Protection will take the form of elevated levees and seawalls (dikes), possibly with addition of “living shorelines.” These take the form of planted berms skirting the levees, which would help absorb wave energy and forestall shoreline erosion.

Installation costs for enclosing the wastewater plant, its treatment ponds and access to them are estimated at $15 million. That would keep dry an estimated $140 million in public and private assets, and keep the current plant operable for as up to 80 years, and possibly more.

Other areas of Arcata and Humboldt Bay will also be developing climate change responses, and regional solutions will likely play a role. Ironically, Arcata’s principal infrastructure-protection measure echoes another issue at the top of the national news. “We’re going to build a wall,” mused Community Development Director David Loya. “And Eureka’s going to pay for it.”

But Arcata’s barrier is no joke. “It’s not, ‘Are we going to build a wall?’ It’s ‘Where are we going to build the wall?’ It makes a lot of sense to make that investment.”

Costs might be covered by a city-wide tax, increased sewer fee, by fees on development in areas likely to be inundated, or other mechanisms.

The result will be a shovel-shaped tongue of land projecting south into an expanded Arcata Bay, with the treatment plan and oxidation ponds at the shovelhead. A startling image provided by city staff shows a sort of isthmus of protected land along South G Street, with areas outside it exposed to the rising tides.

The South G Street corridor to the Arcata Wastewater Treatment Plant. Colored lines indicate levees which will protect it against rising seawater. City of Arcata graphic

“We’ve agreed to look at protecting the peninsula from Samoa Boulevard to the treatment plant,” said City Councilmember Paul Pitino, himself a south-of-Samoa Boulevard resident. “The details will be real interesting to figure out.”

He said moving the plant isn’t feasible, and while he’s “still open to some possible dispersion plants,” walling off the critical facility and a route to it  is inevitable. “We’re going to have to do this soon,” Pitino said.

All of this will require a regulatory overhaul, both locally with Arcata’s Coastal Land Use Element, and with the Coastal Commission. Where protection is appropriate, construction will have to be allowed in some environmentally sensitive locations, with wetland areas inevitably filled. Eventually, another wastewater treatment plant could be built away from the water peril, or multiple mini-plants could spring up around town. By this time, advanced technology might offer other solutions presently unknown. “We might have laser toilets that instantly incinerate poop,” Loya joked. “Or we’re in more of a dispersed model, or have an ocean outfall – lots of alternatives.”

Even areas outside the inundation zone will feel impacts, since higher bay water levels will mean flooding around creeks that won’t be able to drain. That will require a lot of water pumping, as is routinely done in other parts of the world that lie below sea level. “All the low-lying areas of the city are going to have problems,” Loya said.

Accommodation tactics could include designing structures that can tolerate periodic flooding and retrofit of roads and utilities to withstand the onslaught. Arcata may even see the return of boardwalks along city streets, linking upland parking lots to elevated structures.

When the time comes, retreat measures might include establishment of “no building” zones and removal or relocation of structures. Areas safe from inundation could see annexations, zoning changes to allow replication of lost facilities and concentrated development.

As the City Council moves ahead, many more meetings and public outreach will be conducted, and better data acquired. Staff, meanwhile, will be putting specifics to the policies the council could incorporate into the Land Use Plan. But huge and fateful decisions are unavoidable.

“One of the big concerns is to make sure that we’re not putting off the tough decisions on what we have to do to adapt and retreat in some areas,” said Arcata Vice Mayor Sofia Pereira. She’s concerned about residents of South G and H streets, many of whom are low-income families.

Unknowns and uncertainties massively complicate the decisionmaking, especially when extrapolating current data way into the future. “We can make decisions based on the information we have, but past 100 years out there’s really no way to know what will happen,” Pereira said.

A major earthquake and regional subsidence, for example, could change the timeline drastically.

“This is a lot to wrap our head around,” Pereira said. “Whatever we decide now will have impacts for decades.”

Another view of the area initially designated for protection. City of Arcata graphic



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