King Tide Tour provides insight into sea level rise

Dozens of people gathered in the rain at the Arcata Swamp on Saturday January 11 to view the highest tide of the year and listen to a discussion of how it can be seen as a glimpse of the rise of the sea ​​level and the effects it will have on the town of Arcata and the world.

Elliott Dabill, a retired high school biology teacher and current chairman of the Friends of the Arcata Marsh board, which sponsored the event, led a walk along the levees and trails through the marsh, explaining the science behind the King Tide event. The tour also offered fans glimpses of black-crowned night herons and dramatic aerial ballets by flocks of dunlins in flight.

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  • Marc McKenna
  • Sherry Van Fossen photographs the King Tide at Arcata Swamp.

High tides, Dabill explained, occur when the Earth is between the sun and the moon, and at the closest point in its orbit to those two bodies. This combination of events occurs once or twice a year, usually in January, resulting in extremely high water levels along ocean coasts. (This year there will be another king tide in February.) While ordinary high tides are usually around 6 feet, king tides are over 8 feet high. In Arcata Bay, the tide peaked at 8.35ft shortly after noon on Saturday, covering mudflats and salt marshes, leaving dead trees, bushes and small patches of grass eerily sticking out of the water.

In the 1850s, white settlers, in an attempt to reclaim mountainous areas sheltered from the tides, dammed the bay from land, replacing the salt marshes that originally bordered the water with levees. It worked for about 150 years, but now that the ocean is rising due to global warming, high tides are increasing, and eventually today’s high tide heights will become the new normal, occurring frequently. At that time, when an unusual event occurs, such as a large storm or the regular astronomical pattern that creates King Tides, water levels will be so high that they will overtop the levees, creating flooding and making some areas unusable for agriculture and habitation.

“As the sea level rises 2 to 3 feet, it will start to overtake these levees, and then Humboldt Bay will rise by a third,” Dabill said. “The bad news is that your house is in that third.”

“No, that’s not it,” retorted a walker who lives in a remote area of ​​Fieldbrook.

“Some of your houses,” Dabill corrected himself.

“Look at what we have today and imagine it getting worse,” he continued.

“The green zone,” he said, referring to a city map, as the group stood at the edge of the McDaniel Slough seawall near the western edge of the swamp, “is where we stand right now. This green area is going to be underwater.

The most popular parts of the swamp, where people run, walk dogs, ride bikes and watch birds, will be underwater, as will some of the ponds, he said. Part of the swamp that will remain above water, according to the flood map, is the old dump called Mount Trashmore.

“Future passers-by past what was once Arcata will say, ‘What is that high ground over there?’ he said, “‘That was the town dump.'”

“What does Arcata want to do about this?”

“Do more landfills,” someone quipped.

In particular, the city intends to save the wastewater treatment plant, which is currently undergoing major modernization works. It would not be cost effective to build a new facility elsewhere, but to do so the city will also need to protect South G Street from rising waters, which should be a major relief for property owners.

“How would you protect a big piece of land like that?” Dabill asked. “No more dikes. If you hike the trail around Lake Klopp, that big lake over there where the parking lot is, and look back at the sewage treatment plant, you’ll notice that the slope that protects it from the bay is covered in big rocks. And the top of this dyke is really wide. The city has planned for the future so they can build it even more and shield it and grow plants in it. This is called a living slope, where they tilt the land and grow plants that will protect it from the washing of the tides.

The purpose of the Arcata Swamp, Dabill explained, is to provide wastewater treatment for the city, using natural processes instead of chemicals. In a nutshell, when wastewater flows under the root systems of water-loving plants, the bacteria on the roots feed on the nitrogen-rich waste and, by the time the water has spent several weeks drain through a series of ponds, it is clean enough to be discharged into the ocean. (The waste water is disinfected with chlorine before its final dispersion.)

After the upgrade, the chlorine will be replaced with an ultraviolet light disinfection system. The treatment ponds on the south side of the marsh, an area not normally visited by the public, will be protected from the rising bay.

Arcata Swamp was the first in the world to use this innovative yet natural system and since its construction thousands of similar swamp wastewater treatment systems have been built around the world. It’s especially valuable for poor countries, Dabill said, who may not be able to afford a high-tech system but can build or modify a swamp.

But the focus of the day was the tide.

“What you see today as King Tide is tomorrow’s normal tide,” Dabill said. “Sea levels are rising and the reason sea levels are rising is because glaciers are melting around the world and the temperature of the ocean is changing. [and warm water takes up more space than cold water]. The disappearance of the glaciers means that hundreds of millions of people, especially in Asia, will have to move because they will not have enough water.

“If global warming reaches 1.5 to 2 degrees Celsius, then bad things happen. Permafrost is melting releasing methane [an even more powerful greenhouse gas] and more CO2, so a tipping point is reached.

Dabill called for action.

“You don’t have to feel guilty about flying on an airplane, but you have to think about it,” he said. “I am refinancing my house to install solar panels. We must do everything we can and involve the governments.

“This is perhaps the greatest disaster that has ever struck mankind.”

Dabill urged photographers in the group to send their photos to, a website operated by the Coast Commission. The City of Arcata is also collecting photos for use on its own website, at

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