The Humboldt Bay area is experiencing the fastest rate of relative sea level rise on the West Coast. That's because tectonic activity is causing the ground beneath the bay is sinking at the same rate the ocean is rising. According to the California Ocean Protection Council's 2018 projections, sea level in the Humboldt Bay area is expected to rise 1 foot by 2030, 2 feet by 2050, and 3 feet by 2060. In late 2021, scientists reported that Antarctica's Thwaites Glacier is likely to collapse within 5 to 10 years, which could result in an additional 2 to 10.8 feet in sea level rise. The primary impacts from sea level rise are increases in flooding and erosion. Sea level rise will expand the area vulnerable to flooding during major storms, as well as in the rare but catastrophic event of a major tsunami. 
The term 100-year flood is used as a standard for planning, insurance, and environmental analysis. People, infrastructure, and property are already located in areas vulnerable to flooding from a 100-year event. Sea level rise will cause more frequent—and more damaging—floods to those already at risk and will increase the size of the coastal floodplain, placing new areas at risk to flooding.

The edges of Humboldt Bay are on the verge of being overrun by the sea. It laps at the boundaries of Highway 101, surrounds the Arcata Marsh, and sneaks around the corners of low-lying industrial areas in Eureka. 

SINKING SHORELINE

Humboldt’s location at the end of the Cascadia Subduction Zone makes the area more vulnerable to sea level rise than any other location on the California coast. Due to its position in a very active tectonic area and the specific activity of the surrounding plates, the Humboldt County region is steadily sinking, or subsiding. 

The Humboldt Bay Vertical Reference System Working Group is a research group focused on identifying geology’s role in Humboldt Bay sea level rise. In a 2017 report, they found that land subsidence contributes to sea level rise 2 to 3 times more in Humboldt County than anywhere else in California. Of the 18 inch rise in sea levels that has occurred locally in the past century, an estimated 50% is due to tectonic subsidence.

“The ocean isn’t rising any faster off of our coast than it is down in San Francisco, but we have subsidence that the rest of California doesn’t have,” said environmental planning consultant Aldaron Laird. 

Laird has been an essential part of local sea level rise risk assessment and adaptation planning over the last decade, consulting with Humboldt County and various local districts. 

ADAPTATION PLANNING

Humboldt County has commissioned many reports which assess the risk that sea level rise poses to infrastructure and communities. These contextualize what different levels of sea level rise will mean, and suggest possible adaptation measures. However, the reports do not implement the adaptation measures.

The most recent grant-funded project to tackle this issue concluded in 2019, yet none of the recommendations from that, or any other report, have been implemented. 

An area that the reports do not touch on is the potential for industrial contamination in the bay as sea level rise reaches new areas.

In her career as an environmental advocate, Jennifer Kalt has observed the local government’s lackluster reaction to the threat of sea level rise for years. 

“What I have seen as a repeating theme is a lot of local jurisdictions getting grant money to develop plans and then there isn’t a plan,” said Kalt. “It’s a little depressing to see so much planning lead to nothing.”

Michael Richardson is a supervising planner of long range planning in the Humboldt County Planning and Building Department, which is responsible for sea level rise adaptation planning. He said that the county would like to decide on terms of collaboration with other local jurisdictions before they plan to implement any sea level rise adaptation measures. Simply put, they don’t have immediate plans to do anything specific.

“There would be a different process to go forward with getting the cities and the county on the same page and whatever agreements need to be made,” said Richardson. “What that plan looks like is what we’re still figuring out.”

Kalt doesn’t think that the pace at which the government is moving on this issue will make a difference in time. In addition to protecting residential areas, she said that their focus should be on relocating key infrastructure. 

“I’m concerned that a lot of the agencies that need to address these problems, there’s not a lot of political will to do what needs to be done,” said Kalt.

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The county is planning on mitigating the risks of sea level rise along a particularly vulnerable stretch of Highway 101 between Eureka and Arcata by restoring salt marsh.
Restoring about 17 acres of salt marsh along a 1.25-mile stretch of Highway 101 between Brainard and Bracut would reduce the risk of flooding and the erosion of the shoreline for at least a century, Humboldt County Public Works Deputy Director Hank Seemann told the commissioners of the Humboldt Bay Harbor, Recreation and Conservation District on Thursday.
“If sea level rise continues to accelerate, there would be some point in the future where the salt marsh could get flooded out, but our study concluded it would likely have benefits for several decades,” Seemann said.
The Humboldt Bay Natural Shoreline Infrastructure Feasibility Study, which was completed in September, illustrated the most feasible designs and what the shoreline is expected to look like once the project is complete.
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Anchored by the cities of Eureka and Arcata and known for its redwood forests, cannabis tourism and cool, misty beaches, Humboldt Bay also has an unwelcome distinction: It has the fastest rate of sea level rise on the West Coast.
Tectonic activity is causing the area around the bay roughly 300 miles north of San Francisco to sink, which gives it a rate of sea level rise that is about twice the state average. Compared to 2000, the sea in the area is expected to rise 1 foot by 2030, 2.3 feet by 2050 and 3.1 feet by 2060, according to California Ocean Protection Council.
Residential areas, wastewater treatment plants and a segment of Highway 101 that connects Eureka and Arcata are all at risk — especially when the frequent and intense storms associated with climate change trigger more flooding. There are even long-term worries about a nuclear waste storage facility on the bluffs. Yet the region also has become a test case for how to adapt to a problem that faces all of coastal California, including by restoring wetlands that were filled in for logging and farming in earlier eras.
“We say the bay is going to take back from us what we borrowed for the last hundred years or so,” said Jennifer Kalt, director of the nonprofit group Humboldt Baykeeper and a member of the Cal Poly Humboldt Sea Level Rise Institute.
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Sea level is rising more rapidly in the Humboldt Bay region than in any other place on the US West Coast. Cal Poly Humboldt’s Center for Sea Level Rise has been looking at the implications and last Monday, the San Francisco Chronicle gave us feature treatment.Sea level is rising more rapidly in the Humboldt Bay region than in any other place on the US West Coast. Cal Poly Humboldt’s Center for Sea Level Rise has been looking at the implications and last Monday, the San Francisco Chronicle gave us feature treatment.
Sea level rise became news in the 1970s. Studies were published and in 1988 the UN formed the Intergovernmental Panel on Climate Change was formed. Since 1993, satellite altimetry has provided a global picture of the rising oceans. The current estimate of average sea level rise is 3.4 millimeters (.13 inches) per year. There is no gray area here, it is a measured fact.
But the ocean isn’t a bathtub, and the rise is not uniform, rising more rapidly in some areas and dropping in others. How water level changes locally is a function of many variables. The three most important are thermal expansion, the supply of water, and deformation of the sea floor.
Water expands as it warms. A warmer ocean raises sea level with no additional water. Expansion rates are complex and depend on salinity, temperature, and pressure. There are seasonal changes and longer ones. Thermal expansion in strong El Niño years can raise the background tide levels by nearly a foot.
Added water comes from three main sources: valley glaciers, the Greenland ice sheet, and the Antarctic ice sheet. I called them the three dominos when I taught about sea level rise. Alas, the valley glaciers are nearly gone and much of their contribution is already in the ocean. Melting of the Greenland ice sheet is well underway and all eyes are now on Antarctica. It will be the primary driver of sea level rise over the next century.
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Forty-four feet isn't all that high. It's halfway up the tall side of the county courthouse. If you stacked Guy Fieri seven-and-a-half times on top of himself, his platinum blond hair would reach 44 feet high. Forty-four feet is also the height above today's sea level where 37 tons of radioactive waste from the former PG&E Humboldt Bay power plant is entombed in a concrete vault at the edge of the bay. A new coalition called, you guessed it, 44 Feet has brought together state agencies, federal and local political interests, scientists, a few folks with no titles at all and, to some extent, the nuclear plant's owner, PG&E. Like nanoplastics and deep-fried butter, most of us do not want to think about radioactive waste stored nearby, but 44 Feet is trying to plan for its future safety, even if that future is 100,000 years away.
PG&E's old nuclear power plant sat next to U.S. Highway 101 at King Salmon. It ran a brief and ignominiously leaky life from 1963 to 1976. Still, it produced high-level radioactive waste from the uranium fuel it used to create electricity. The radioactivity has cooled somewhat in the intervening years, but it will remain hot and toxic for more than 100,000 years.
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