Sea Level Rise

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 to sink at the same rate that the ocean is rising. According to the California Ocean Protection Council's 2024 Science & Policy Update, sea level in the Humboldt Bay area is expected to rise approximately 1.5-2 feet above 2000 levels by 2060 and 3.9-5.5 feet by 2100. 
The primary impacts from sea level rise are increases in flooding, erosion, and rising groundwater. Sea level rise will expand areas 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. 
NEW! Now you check out our interactive map of two sea level rise scenarios for the Humboldt Bay Area! Featured are scenarios showing 1- and 2-meters above Year 2000 water levels. For many years, these have been static maps with no simple way for the public to examine points of interest. Now, people wondering if their neighborhood is at risk can zoom in on locations and see street names, etc. 

 

A coalition of advocates, academics and government officials are throwing their weight behind a regional strategy to address future sea level rise.
They argue that, for the plan to work, state regulators spearheading the effort need new authority to implement it — a policy idea that many stakeholders agree is necessary, but that would require the equivalent of a political Hail Mary pass.
At the moment, preparing for rising seas is mostly a free-for-all. Counties, cities and developers are coming up with plans separately and not all to the same level of protection, which has created a patchwork of inconsistent zoning and differing interpretations of state law.
For the regional plan to succeed, San Francisco Bay Conservation and Development Commission (BCDC) needs to treat front-line communities as climate experts, said Julio Garcia, a BCDC environmental justice adviser and director of the nonprofit Rise South City, which focuses on climate issues in South San Francisco.
Will Travis, former executive director of BCDC, suggested the state create a different agency to enforce sea level rise adaptation across California.
“For there to be any kind of a regional strategy for dealing with sea level rise, you can't just expect that local government by local government will do the right thing,” he said.
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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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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. 

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. 

Hagedorn suggested water authorities should instead take a new look at hazardous waste sites that are currently considered remediated. Hagedorn suggested water authorities should instead take a new look at hazardous waste sites that are currently considered remediated. 

“There are a lot of older locations, some dating back to the 1970s or even the 1950s when remediation technologies were not what they are now, that may still contain a lot of contaminants,” he said. 

Additional remediation may be necessary to prevent these toxins from becoming mobilized as the water tables rise in the soil.

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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. 

More Articles …

  1. Humboldt County plans to use living shoreline to mitigate sea level rise between Brainard, Bracut
  2. What sea level rise, tectonics mean for North Coast
  3. This part of California has the fastest sea level rise on the West Coast. Here’s what’s at stake
  4. 500-Year Floods Coming to New York Every 24 Years, Study Says

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