2.4 Rockslides Result in 12-day Full Closure on US-101 Along North Coast of California During Late April 2017

Monday, 8 January 2018: 11:15 AM
Ballroom D (ACC) (Austin, Texas)
Richard Lam, NWS, Eureka, CA

The North Coast of California, which includes the communities of Eureka and Fortuna in Humboldt County, and Crescent City in Del Norte County, has around 160,000 residents. This rural region, said to be “behind the Redwood Curtain”, has only two major highways and two secondary highways providing access in and out of the region. One of the major highways, US-101, provides the most direct link between Eureka and the San Francisco Bay Area. During the winter of 2016/2017, Northwest California experienced one of the wettest rainy seasons on record. As a result of the saturated ground and numerous heavy rainfall events, a number of mudslides and rockslides took place along the major highway corridors.

This literally closed the Redwood Curtain on Northwest California, which severely limited emergency services and commercial access to the North Coast. According to CalTrans District 1, the estimated cost for road repairs exceeded $180 million for the season. The most significant rockslides took place along US Highway 101 and US Highway 299 in northern Mendocino County and Central Trinity County, respectively. The major slide on US Hwy 101 led to a complete closure of the road for 12 days, from April 16 to April 28. This highway closure resulted in hardships for Humboldt County residents, as access to medical and business services were cut off for the better part of 2 weeks. Furthermore, the trucking industry had to endure lengthy detours and increased expenses due to 2 or more hours of additional driving caused by re-routing. With emergency repairs, only partial access to Highway 101 was restored, and it was near the end of May before full access was reestablished.

Weather clearly played a significant role in this event. An anomalously wet winter, combined with periods of intense heavy rain caused by a landfalling atmospheric river during the middle of April, were key factors contributing to this high impact weather event. Using pattern recognition techniques, NWS Eureka will improve forecast skill for future atmospheric river events. The improved recognition of these events will result in better Impact-Based Decision Support Services to a range of core partners. This will ultimately help communities in Northwest California better cope with these high-impact events.

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