What is today’s king tide will be tomorrow’s normal tide.
The recent king tide reached its peak of 8.35 feet on Saturday just after noon, providing a window into what normal tides will look like in the future and identifying potential vulnerabilities to local communities along Humboldt Bay.
Tides rise when the gravitational force of the sun and moon pull the ocean toward them and fall when the sun and moon are farther away. In January every year, the Earth is a little bit closer to the sun, and that means the sun has more gravitational pull on the water, said Elliott Dabill, board president of nonprofit Friends of the Arcata Marsh, on Saturday at the Arcata Marsh and Wildlife Sanctuary during the third annual king tide tour.
The same could be said of the moon, which orbits around the Earth in an elliptical shape, he said.
“All of that comes together at the king tide,” Dabill said.
As the ocean absorbs more heat as a result of increasing greenhouse gas emissions in the atmosphere, it expands, Dabill said. Melting ice in the Arctic and Antarctic are also adding more water to the oceans, leading to an increase in sea levels, he said.
“You can see a clear trend of tides going up over the last 40 years,” said environmental planning consultant and local sea level rise expert Aldaron Laird during a packed talk on rising tides in Humboldt Bay at Six Rivers Masonic Lodge on Friday. ” … What we like to call today king tides, those are the tides that will be the vehicle for change.”
King tides will be when dikes are breached or overtopped, identifying areas that will be vulnerable to flooding, he said.
A series of dikes that were put in along the bay in the late 1800s by land speculators trying to create agricultural land out of a salt marshes are still the only protection for critical infrastructure, such as sewer lines, power lines and Highway 101, that would be vulnerable if those dikes were to erode or get overtopped, Laird’s research showed.
“We don’t really have a problem right now of sea level rise,” Laird said. “We have a problem with historical legacy that we inherited from the 1890s.”
Those dikes run across 670 parcels and “there’s no shoreline management district” that maintains those dikes, Laird said.
The dikes are under the jurisdiction of the California Coastal Commission, which regulates land use along the state’s coast, but that body isn’t making decisions with climate adaptation in mind, Laird said, as it recently approved two housing developments in King Salmon, which routinely floods.
There are ways to reinforce the dikes without building them up higher, Laird said, such as using a living shoreline, such as a salt marsh, to reduce the impact of waves on the dikes.
However, there’s already about 10 meters, or 33 feet, of sea level rise locked in, Laird said, which won’t happen all at once, but sea level rise projections are changing all the time and it’s hard to predict when that will happen.
“We started in 2010. The state said you have to project 3 feet of sea level rise by 2100 in all of your work,” Laird said. “And now they’re talking about 3 meters of sea level rise by 2120, so it went from 3 feet to almost 10 feet.”
The dikes won’t be able to protect what’s behind them after a certain degree of sea level rise has taken place because it will also cause the ground water to rise above the surface, Laird said.
The key is to plan to relocate to higher elevation areas that won’t be inundated by the projected sea level rise that is already expected to take place, he said.
For more information, visit coastalecosystemsinstitute.org.