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 above 2000 sea level as much as 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. But these extreme storms are happening with increasing frequency, in part due to rising seas. 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.
To view sea level rise scenarios for the Humboldt Bay area, visit NOAA's 2022 Sea Level Rise Viewer and go to the local scenario for the North Spit.     

Interactive Map of King Tide Photos

The California Coastal Commission's King Tide Photo Project features photos from the Humboldt Bay area and across the state. Anyone can upload photos online or via a smartphone app.

Click HERE to upload yours.

Left: Erosion along New Navy Base Road in Samoa during the December 23-24, 2022 King Tides. Photo by Jen Kalt.

The new year is a make-or-break moment for a Richmond housing development atop a contaminated former waterfront site once owned by the global pharmaceutical company AstraZeneca.
Plans for developing as many as 4,000 units on the site have survived scrutiny by officials and legal challenges from environmental groups; the Richmond City Council approved the development years ago.
But last summer, state regulators asked the company to examine whether future sea level rise pushing up groundwater should alter the cleanup remedies for the hazardous site before development begins.
“The science of sea level rise is progressing, we're listening to the community, and we're saying we want more evaluation,” Ian Utz, project manager for the California Department of Toxic Substances Control, or DTSC, told KQED. "We're going to follow where the science leads us. The sea level rise evaluation is not a one-and-done thing."
Utz also tasked two independent researchers to analyze the company's site-wide sea level rise evaluation. AstraZeneca determined that by the year 2050, the site would incur no negative impacts.

The National Weather Service in Eureka issued a coastal flood warning on Thursday in anticipation of anomalous high tides that hit early Friday. While there were few issues caused by the flooding, the king tides offer a preview of what future sea level rise could mean for Eureka and the rest of Humboldt Bay.
“This is about one foot higher than a typical high tide,” said Jennifer Kalt, director of the nonprofit Humboldt Baykeeper. “With one foot of sea level rise, what we saw today will be the average monthly high tide.”
In fact, the astronomical tide event was even higher than expected as it reached a peak of 9.28 feet in the North Spit. But other fortunate weather factors helped mitigate any risk of damage from flooding.
Only within the past decade are geologists realizing that the area around Humboldt Bay is sinking due to tectonic subsidence. The average sinking is at nearly the same rate that sea levels are rising, compounding the effect and doubling the relative sea level rise. In contrast, Crescent City appears to be on a tectonic uplift that would minimize the effects of rising sea levels. And for better and for worse, the science at the core if this issue is still fairly new; the theory of plate tectonics only came to be understood in the past 75 years.
“A lot of this science is advancing,” said Kalt. “10 years ago, no one knew that the Humboldt Bay area was sinking so rapidly due to tectonic subsidence.”
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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. 

Droughts and sinking groundwater levels due to climate change and water consumption have become a familiar worry in many parts of the world. But coastal California is poised to soon encounter a very different kind of problem: Levels of groundwater may rise. 

“It’s a concern,” said Ben Hagedorn, Associate Professor of Geological Sciences at California State University Long Beach. 

“What we see near the coast is that the rising sea level pushes up the saline groundwater,” he said. 

In the process, the fresh groundwater used for drinking gets pressed toward the surface as well since it usually floats on top of the heavier salty groundwater. This could make coastal regions more prone to flooding, but there are also more insidious consequences. 

As the rising fresh water seeps into surface soils, toxins such as cadmium and lead from hazardous waste sites, landfills and other contaminated areas could get flushed into drinking supplies, Hagedorn said. 

Rising levels of fresh groundwater could make this problem more widespread and also wash toxins from shallow aquifers into the deeper reservoirs that currently provide drinking water. And soluble pollutants aren’t the only concern. 

“When you have plumes of contaminants in aquifers, they can degas and generate toxic vapors,” Hagedorn said. These vapors can then push into buildings through cracks in the construction material or via utility lines and low-elevation windows.

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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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