State weighs options for Last Chance Grade

Paul Mann
Mad River Union

EUREKA/CRESCENT CITY - In consultation with the public, state transportation officials are evaluating emergency construction plans that would deal with a potentially catastrophic roadway failure along the Last Chance Grade Complex south of Crescent City.

The California Department of Transportation (Caltrans) proposals range in price from $320 million to $1.6 billion with $100 million in federal emergency funds needed from Congress to get the initiative rolling.

A Project Study Report is due in July.

The Last Chance Grade (LCG) is a four-mile segment of U.S. Highway 101 just north of Wilson Creek in Del Norte County and about 10 miles south of Crescent City.

Officials say the slide-prone corridor is vital to Del Norte/Humboldt commerce and tourism. A complete failure, now or later, would cut off detours and isolate the North Coast even further.

The near-term Caltrans options are:

• A low-end reconstruction of Last Chance in-place, taking days to weeks, to rectify a small-scale slip-out that causes a minimal movement of the roadway.

• A more ambitious project to move the roadway farther from the ocean. This would be in response to a “moderate slip-out,” which hasn’t occurred to date. The existing roadway alignment would have to be changed and Caltrans would have to cut into the hillside, with an impact on old-growth redwood trees.   

• A realignment in response to a large landslide that causes the roadway to collapse. That would require cutting into the hillside, however deeply, to re-position the roadway in full. In the meantime, a one- or two-lane temporary access road would allow traffic flow.

Other preliminary alternatives envision a tunnel, whose length and location would vary based on which engineering solution gets the nod.

Projected revamp lengths range from 1.3 miles to 11.7 miles, affecting as much as 330 acres of land and a number of streams.

Construction proposals call for a maximum seven percent grade and a two–lane highway with truck passing lanes. The lanes would be 12 ft. wide with 8 ft. shoulders. The design speed is listed at 55 mph. with a minimum turning radius of 1,100 ft.

Although the complex is considered safe to use for the time being, a 2000 geologic study mapped more than 200 historical and active landslides within the corridor, both deep and shallow. Landslides have moved the roadway more than 50 feet horizontally since it was realigned in 1937.

From 1981 to 2012, $36.2 million was spent on retaining walls, roadbed overlays, drainage improvements and slip-out/washout repairs. From 1997 to 2012, the cost was $29.3 million.

In the event of the full collapse of the geologically unstable four-mile grade, damage to the Del Norte and Humboldt County economies could reach $130 million in lost job income and $300 to $400 million in reduced annual output, Caltrans estimates.

Some 3,000 to 4,000 North Coast jobs might be lost, which the precarious regional economy could ill afford.

Those potential economic losses and the fact that climate change may generate more severe storms more often make a permanent solution essential, Caltrans says.

The initiative has the broad support in principle of state and federal legislators, including Rep. Jared Huffman (D-2nd District), as well as many North Coast agencies and tribes.     Pending release of the July project study, Cal Trans hosted three town halls last week, the first at the Wharfinger Building here, followed by forums in Crescent City and Klamath.

About 60 people attended the Wharfinger briefing, where LCG Project Manager Sebastian Cohen cautioned that federal emergency relief funding allocated by Congress is limited to $100 million dollars a year. Stringent requirements must be met to qualify, including environmental studies and permits. Improvements, for example an additional lane, are prohibited under the federal guidelines.

“It’s a pretty significant challenge, but it is a possibility,” Cohen said.

Regarding safety, he assured the audience that Caltrans operates a near-real-time monitoring system and conducts daily field inspections. It also carries out regular topographic field surveys to measure changes in elevation. Aerial tracking is conducted with the assistance of the U.S. Coast Guard and the California Highway Patrol, to monitor slope erosion and other geologic changes that might signal an imminent slide.

To buttress monitoring, Caltrans will be installing a number of web cameras and additional lighting, while also augmenting the meager power supply, Cohen said. More retaining wall repairs are in training as well.

In the meantime, the project manager added, Caltrans will have an “initiation document” ready in June. It is the baseline for requesting funding from a variety of sources, in tandem with federal emergency relief money.


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