Summary and Recommendations

On January 28, 2021, a portion of Highway 1 was eroded at Mile Marker 30 just south of Esalen, California, and north of Lucia, California. This closure of Highway 1 resulted in a detour of 150 mi (241 km) for residents. The embankment failure was caused by a series of aggravating events that started with the 2020 Dolan wildfire, which generated debris and increased surface water flow, followed by an atmospheric river that led to 11.8 in. (300 mm) of rainfall in the Rat Creek area and resulted in significant surface water runoff. Modern techniques can support a system-level monitoring and assessment of Highway 1 that recognizes that the drainage basins are different in size, geology, topography, and susceptibility of landslides and debris flows. New techniques for monitoring can be used to support the maintenance of the highway and to keep focus on the most critical areas of the system compared to less susceptible ones.