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 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.

Scientists study an unexpected climate change problem: Rising groundwater levels

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.

Sea Level Rise Threatens Humboldt, Local Government Stalls

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.

What sea level rise, tectonics mean for North Coast

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.

Humboldt County plans to use living shoreline to mitigate sea level rise between Brainard, Bracut

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.

This part of California has the fastest sea level rise on the West Coast. Here’s what’s at stake

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.