Rancho Palos Verdes faces deeper, larger landslide threat, city report says
City leaders of Rancho Palos Verdes learned they are dealing with land movement from a much deeper active slide plane than previously thought, leading to mitigation efforts to expand beyond the Portuguese Bend landslide area.
In a Portuguese Bend Landslide update Tuesday evening, Mike Phipps, the city's geologist, said that while the landslide's movement has leveled off at 3.5 to 4.5 feet per month, a much deeper slide is moving much faster.
Recent testing of underground conditions found a larger, deeper slide moving quickly at a depth it has never moved in recorded history. "There's been no recorded movement of that deeper Ancient Altamira slide," Public Works Director Ramzi Awwad said. "This is completely new, this is completely new and unprecedented."
The five shallow slide areas, including the Portuguese Bend Landslide Complex, the Abalone Cove Landslide Complex and the Klondike Canyon Landslide Complex, and Beach Club Landslides, are all sitting on top of the Ancient Altamira Landslide Complex.
City staff said they had been tackling management of the shallower slide areas individually, but that strategy will have to change.
The Portuguese Bend location, where SoCal Gas cut off service to over 130 homes to protect public safety, will no longer be addressed independently, city staff said.
Stabilizing the series of landslides that comprise the Ancient Altamira Landslide Complex, is to be done in a unified and coordinated approach.
Trying to manage it all previously, city leaders invested in a $10 million emergency hydrauger project. The two hydraugers, called dewatering wells, act as underground drains to extract water that contributes to land movement.
The project will have to be adjusted to address the deeper plane. The recommendation is to drill dewatering wells at a deeper level to relieve some of the water pressure. That drilling is expected to begin in weeks.
City councilmembers also agreed to expand the emergency hydraugers project to include the shallower slides.
