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Slippery Slope

An overhead view of Highway 101 adjacent to Last Chance Grade shows how close the slide-prone slope is to to the road. Del Norte Triplicate / Bryant Anderson
An overhead view of Highway 101 adjacent to Last Chance Grade shows how close the slide-prone slope is to to the road. Del Norte Triplicate / Bryant Anderson
North Coast one of 19 regions studied for climate change impact on highways 

Multi-million dollar transportation projects are meant to outlive their planners by decades, but how do you build long-lasting infrastructure in light of the dynamic world created by climate change?

The Federal Highway Administration is funding studies on what infrastructure is most vulnerable to the effects of climate change and extreme weather, and the North Coast is one of 19 pilot areas across the country going under the microscope to study how to deal with a changing world.

The active slide known as Last Chance Grade on U.S. Highway 101 south of Crescent City received specific attention since sea level rise from climate change is expected to increase erosion at Last Chance, which has already cost $29 million in stabilization measures since 1997 alone.

“If we’re going to spend millions to build new infrastructure, and it’s going to last 100 years, we need to predict what the world will look like then,” said Rob Holmlund, a planner with GHD, the consulting team performing the study, during a public workshop with the Del Norte community on Tuesday night.

For Del Norte, the most significant climate change-related impacts that scientists predict are rising sea levels and heavier rainfall — both of which contribute to increased erosion and, as a result, landslides. Flooding along low-lying sections of highway near the ocean is also a concern. 

“Your king tide (the highest tide that happens only a few times per year) today will be the normal by 2050,” said Jessica Hall, a landscape architect with GHD, during Tuesday’s workshop. 

If global carbon emissions are not drastically cut in the near future, scientists predict that by 2100 the ocean could be as much as 55 inches above current levels.  Although Arctic and Antarctic ice-melt will be one of the main contributors to sea-level rise, higher ocean temperatures will also cause the ocean to swell and expand in an effect known as “thermal sea level rise,” Hall said.

The GHD team evaluated all of the problem areas in Del Norte, Humboldt, Mendocino and Lake counties, which comprise Caltrans District 1, and was awarded a federal grant for the study. 

Del Norte’s notably vulnerable spots include U.S. Highway 101 a half mile south of the Oregon border; the Dr. Fine Bridge on 101; the section of 101 adjacent to South Beach just south of Crescent City; the Wilson Creek Beach section of 101; and the Last Chance Grade slide on 101.

For Last Chance Grade, GHD identified possible adaptation strategies for this area to cope with coming effects of climate change.

The other three areas are South Highway 101 along Humboldt Bay north of Eureka; at the mouth of the Garcia River (south of Point Arena); and along portions of State Route 20 (northwest of Clear Lake), which are all expected to be subject to greater and more frequent flooding as a result of climate change.

The team from GHD broke down ways that communities can react to natural forces caused by climate change:

• Defend — The most aggressive method for facing climate change would attempt to keep current roadways in place by creating defensive measures. Sea walls, flood walls, levees and dykes would all fall in this category.  ‘Defend’ is what Caltrans has been doing at Last Chance Grade, building multi-million dollar contraptions to keep the hill from sliding.

• Adapt — Try to work with the natural forces of climate change.  Floodable bridges, raised bridges and raised roadways are types of “adapt” methods.  For Highway 101 at South Beach, this could mean building a raised roadway so sea level rise does not affect the highway.

• Planned retreat — Do not attempt to “adapt” or “defend” against the forces of climate change. Instead, move transportation infrastructure away from the affected areas.  For Last Chance Grade this would mean rerouting of the highway to a hillside not teetering above the ocean.  For Humboldt Bay, this could be an unwise decision since utilities like sewer and power lines would have to be abandoned.

• Forced retreat — his is the “do nothing” option that ultimately leads to natural forces having their way with infrastructure and humans being forced to catch up. For Last Chance Grade, this is the much-feared complete failure of the roadway, forcing Caltrans to reroute the 101 after it collapses into the ocean.

Although workshop participants seemed almost solely focused on supporting the rerouting of Last Chance Grade, GHD’s Holmlund emphasized, “We are not here to solve Last Chance Grade.”

GHD staff asked everyone to rank what they valued most in planning decisions for future infrastructure in light of climate change, and most Del Norters looked for whatever option coincided with re-routing 101 around Last Chance Grade, regardless of climate concerns.

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