According to the latest projections, sea level in the Humboldt Bay area will rise 1 foot by 2030, 2 feet by 2050, and 3 feet by 2060. 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.

A new study on high tide flooding predicts that the mid-2030s could be catastrophically wet in U.S. coastal regions — and it could stay that way for an entire decade.

Led by members of the NASA Sea Level Change Team from the University of Hawaii, the study says that high tide flooding could happen more frequently on several U.S. coasts. Flooding at high tide, often called nuisance flooding, already occurs with regularity in many coastal communities as water routinely sloshes into streets, yards and businesses.

Two factors could converge to worsen flooding at high tide, the study says: rising sea levels fueled by climate change — and the moon.

The moon's orbit is due for its regular "wobble." That is entirely natural, NASA says, and it has been recorded as far back as 1728. Half of the moon's 18.6-year cycle creates lower high tides and higher low tides; the other creates higher high tides and even lower low tides.

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As the world celebrates Earth Day 2021, local experts warn the historic Arcata dikes holding back Humboldt Bay will be overtopped monthly, possibly in as soon as 30 years, due to rising sea level from climate change. 
"There is no stopping sea level rise for the next century or next couple of centuries," said Aldaron Laird, an environmental planner specializing in local sea level rise who is currently working with Greenway Partners on several local projects. "It's just going to keep right on going."

Wiyot Tribe Natural Resource Specialist Adam Canter said Arcata has a site on McDaniel Slough that is at risk — one of 52 Indigenous cultural sites around Humboldt Bay that could be inundated in the coming decades.

Jennifer Kalt, director of Humboldt Baykeeper, identified three sites in Arcata that are at risk of tidal inundation in the coming decades that have tested positive for dioxin contamination: one on Janes Creek, another on Butchers Slough and the former Little Lakes Industries site off I Street near the Arcata Marsh and Wildlife Sanctuary. 
Last year the Arcata City Council voted to submit an application for a federal assessment grant of $300,000 for the same property and received the grant earlier this year.Last year the Arcata City Council voted to submit an application for a federal assessment grant of $300,000 for the same property and received the grant earlier this year.
Arcata Community Development Director David Loya said he is hopeful that the city will get the cleanup grant and the cleanup will begin as early as this fall, but he anticipates next summer is more likely.
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Aldaron Laird has been studying the effects of sea level rise on the Humboldt Bay for the past 10 years. He says that Humboldt Bay is experiencing the fastest rate of sea level rise on the West Coast because the bay sits on a tectonic plate that is being pulled down as the sea level rises. Laird told the Outpost that over the past 100 years or so the waters around the bay have risen around 12 to 18 inches. 

 

About 75 percent of the shoreline around the bay is artificially made, with a majority of it being earthen dikes from the late 1800s. Laird said there are 41 miles of dikes and that they are nearing a critical moment. 

 

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The small, coastal community of King Salmon in Humboldt County, California is likely at the highest risk of relative sea-level rise on the entire U.S. West Coast. Relative sea-level rise includes vertical land motion, in addition to changes in water level. King Salmon experiences rising waters at a rate nearly three times the global average because the land is sinking due to tectonic activity (earthquakes).
This community experiences flooding regularly, today. Like the rest of the world, it’s projected to get worse, and at an accelerated rate. In addition to water intruding from the Humboldt Bay, King Salmon also experiences flooding when groundwater rises with changing tides and storm surges. Plus there’s a nuclear plant there that ceased operations in 1976, where spent nuclear fuel is still stored on site, vulnerable to inundation. The average income within the community remains low, so many are unable to afford adaptation methods, multiplying the threat of rising seas. 

As scientists throughout the world describe the mounting impacts from climate change and the accelerating timeline in which they’re expected, KEET sits down with three local experts to discuss what Humboldt County can expect in the decades ahead. The county, these officials warn, will be among the worst hit in the state.