Background
About the Portuguese Bend Landslide Remediation Project
The 240-acre Portuguese Bend Landslide is part of a larger complex of ancient landslides located on the south side of the Palos Verdes Peninsula in Rancho Palos Verdes. It was reactivated in 1956 by Los Angeles County’s extension of Crenshaw Boulevard and has been moving ever since, becoming one of the largest continuously active landslides in the U.S. and moving homes by hundreds of feet over the years. The land moves because of the dynamics of surface water percolating into the ground and water trapped deep underground, sliding as much as 8.5 feet per year. The City spends approximately $1 million annually resurfacing a portion of Palos Verdes Drive South that is continuously shifting and cracking due to the landslide. In 2017, the City restarted efforts to explore options for long-term stabilization, forming a City Council Subcommittee to begin a collaborative effort with the community, holding public workshops and hiring a consultant to conduct a feasibility study. The City Council approved a project concept based on the feasibility study in 2019.
The science of landslides is well understood by geotechnical engineers — water facilitates landslide movement. The Portuguese Bend Landslide Remediation Project would remove water trapped deep underground and prevent rainwater from entering the ground in the future. This would be achieved through a combination of the following project components:
- Infilling fissures in the earth to prevent rainwater from entering the ground and contributing to movement
- Creating a surface drainage system using materials reflective of the surrounding environment and planted with native vegetation to convey rainwater to the ocean and prevent it from percolating underground
- Installing hydraugers (horizontal dewatering wells) to extract water trapped deep underground
Similar measures have been successfully implemented at the adjacent Abalone Cove Landslide, which has comparable geologic conditions.
The project has been modeled to reduce land movement to 1-2 inches per year and drastically reduce the threat of sudden movement that could result in the failure of Palos Verdes Drive South, a major road connecting the Peninsula and the City of Los Angeles. If the street were to be severed by sudden major movement — as happened in the neighboring community of San Pedro in 2011 during the Paseo Del Mar Landslide — it would bifurcate the City, creating an over 15-mile detour and eliminating a major connector and evacuation route for the high fire risk Peninsula. Roadway failure could also send raw sewage spilling onto the ecologically sensitive shoreline and ocean from above-ground sanitary sewer trunk lines that serve thousands of homes.