Where Will Sea Level Rise Strike First? – January 5, 2011
Kevin L. Hoover
HUMBOLDT BAY – While the rest of the state tries to make do with water resources strained to the maximum, Northern Humboldt has the opposite problem with its oversupply of Mad River water. And before long, still more water will be coming at us, creating problems from the other direction.
Rising sea levels due to climate change pose an unprecedented challenge for coastal communities. In Arcata Bay’s case, the coming high water threatens to flood critical salt marsh habitat if it can’t migrate inland with the rising sea level. Also at risk are human-made infrastructure such as the railroad, roads, bridges and tide gates as well as agricultural property.
While politicians waste time bickering over climate change and how it does or doesn’t fit into their ideologies, technocrats are busy figuring out what will go under first and where.
A groundbreaking new study undertaken by environmental planner Aldaron Laird, who is also a Humboldt Bay Municipal Water District director, is revealing the extent of the challenge posed by the rising sea level to Humboldt Bay .
Photos taken during high tides and several storms in and around the recent solstice make clear the problem.
The state has instructed relevant agencies to plan for 16 inches of sea level rise by the year 2050 and 55 inches by 2100. Shockingly, says Laird, “No one has taken a comprehensive look at Humboldt Bay’s shoreline yet.”
Working from a$33,300 grant from the Coastal Conservancy, Laird is conducting a thorough inventory and mapping of the current shoreline conditions on Humboldt Bay. “I’m breaking the shoreline up into smaller segments to identify what it’s composed of,” Laird said.
The basic distinction is between natural shorelines and artificial ones such as dikes. One of his findings was how heavily altered the Bay’s edges are. “There’s not much natural shoreline left, less than 10 percent” Laird said.
Also needing work are some of the area’s levees, many of which were created long ago with minimal to no engineering and have not been maintained.
One worst-case example are the dikes near Tompkins Hill Road, created – “built” might be overstating it – in the 1890s and 1900s simply by piling up dredged mud.
Located near the Humboldt Bay National Wildlife Refuge, the dikes are heavily eroded, with failure all but imminent. “It looks like the bay is about to come in,” Laird said. “There are a lot of dikes like that.”
Laird notes that a single point of failure in a levee can flood the entire area the levee is intended to protect.
Unless something is done, Laird said, “the Bay will recover much of its former tidelands.”
During recent high tides and stormwater runoff the Bay has already overwhelmed Indian Island and the Wiyots’ sacred Tuluwat Village. “All the salt marshes are underwater on Indian Island,” Laird observed. “I thought that was pretty dramatic.”
Using 2009 aerial photography, Laird will map the current shore based on whether it is natural or human-made, rocked or eroding. He’ll also build on an earlier tide gate inventory to locate additional tidegates or drainage structures.
Once Laird’s computer mapping is complete, he’ll “ground truth” his findings by walking or kayaking the shoreline at various tides to check, for example, which levees have been undercut and eroded.
In the final phase, the GIS database will be queried to quantify shoreline conditions. The final product will be made available to all relevant agencies and local cities, and will also be available to the public. Laird is also planning to create photo album of Humboldt Bay’s shoreline in Google Earth.
“I hope it’s just the first of many projects of this nature on Humboldt Bay,” Laird said.