Rancho Palos Verdes officials warned residents Tuesday night that there’s a much larger, deeper landslide underneath the shallower movement they’ve been monitoring, raising the stakes for properties that have already seen heavy damage.
It was the first significant landslide update from the city’s geologist in more than a month. Earlier this month, city officials said the inspections were necessary for dozens of homes to make sure structures were safe to inhabit and for emergency responders to enter in an area that had seen land movement of up to 13 inches a week.
The unprecedented land movement also forced the complete dismantling and relocation of this historic Wayfarers Chapel earlier this year.
Ramzi Awwad, the public works director, told the City Council that the deeper slide is moving much faster, and means their stabilization strategy needs to be changed to tackle the landslides as a whole, rather than individually.
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“This is completely new and unprecedented for the city,” he said during Tuesday’s meeting.
Details on the deeper movement
It’s been more than two months since the city started drilling boreholes with the goal of finding where water has concentrated underground. Once it's located, the plan has been to pump it out with hydraugers to ease the weight and hopefully slow the slide.
City geologists started to suspect the landslide was moving on a deeper plane than what the hydraugers were targeting. They tested this by drilling the boreholes much deeper than they had planned, according to a 76-page report that details the scope of the movement.
They found the shallow plane about 165 underground, but Awwad said they also discovered a deeper plane about twice as deep, believed to be the Ancient Altamira landslide complex.
“The shallower slide does have fast movement, but the deeper slide is moving much faster,” he said during Tuesday’s meeting. “It's moving several times faster than the shallower slide.”
City manager Ara Mihranian added that they believe it’s moving as one larger landslide rather than each area independently.
The previous strategy of tackling the slides separately is no longer recommended. The deeper plane has become the priority, although they still need to deal with the shallower movement.
The staff report described it as “a ‘bowl’ within a bigger ‘bowl.’”
What else has changed
Mike Phipps, the city geologist from Cotton, Shires, and Associates, Inc., said the rate of land movement has leveled off, but that doesn’t mean it’s stopped.
“It's sort of akin to driving on the freeway,” he said. “You get on the onramp, and we've been accelerating this landslide since late 2022, and all the way through 2023 we've been speeding up on that freeway, and now we've reached cruising speed.”
The movement has decelerated in some spots, and accelerated in others. But overall, the landslide areas are now moving roughly 88 times faster than in October 2022 and continue to severely impact trails, open spaces, public and private roads, hundreds of residential structures, and utility infrastructure.
Phipps noted they’ve been keeping an eye on some new areas, including Burma Road.
“Now it's showing consistent movement and it's creeping at about a half an inch per week,” he said. “So that is a potential new area that will expand the area of major movement, more acreage.”
The fastest movement is in the middle of the entire landslide complex, and Phipps added that’s one of the “hallmarks” that it’s all moving as “one big unit” now.
What about the emergency hydraugers project?
The project, which includes a pair of $5 million hydraugers, has to be adjusted for the deeper plane, Awwad said.
“We need to take some risk,” he said. “Implement some measures knowing that they're not guaranteed to succeed, but coming up with the best possible scenario given these difficult circumstances.”
The city geologist team has proposed deep vertical wells that will pierce the deeper plane to relieve some of the pressure.
They also proposed expanding the borehole program to learn more about other areas of the slide.
This deep slide is likely responsible for the recent ground cracking and accelerated movement in other parts of the landslide complex, including the Klondike Canyon and Abalone Cove areas.
Water has been confirmed within the Portuguese Bend landslide, as well as in and below both the shallower and deeper slide surfaces, which could create pressure on both. The ongoing movement has also formed bulging along the beach, according to the city report.
How it's impacting the neighborhood
Gas lines, electric poles, roads, water mains, and sewer pipes have all been afected by the movement, according to the city, causing fissures, sinkholes, cracking, and shear zones, among others.
The city manager has temporarily closed large parts of the nature preserve, including about 10 miles of trails, for safety concerns. Extensive repairs are expected before they can be reopened, according to the city.
Some parts of Burma Road are no longer accessible by car, and are even challenging to get through on foot. And near the lower Rim Trail, you’d need step stools or ladders to get past the drops of 15 feet or more.
“Many locations are almost unrecognizable, with little to no trail remaining,” the city report states.
What’s next
When asked when they could start drilling, Awwad said they’re hoping to start in weeks, if not sooner.
He told LAist in a follow-up interview Wednesday that the deeper slide plane will be targeted by vertical dewatering wells with the goal of extracting the water underneath. The hydraugers will target the shallower slide, so they’ll go under that plane, but not the deeper one.
“It seems like right now, we need to do something, period,” Councilmember Barbara Ferraro said. “I mean, whatever we can possibly do that relates to stabilization, we need to do it yesterday.”
The Rancho Palos Verdes City Council agreed to expand the scope of the emergency hydraugers project to include the Greater Portuguese Bend Landslide complex, the deeper slide complex, Abalone Cove, Portuguese Bend, Klondike Canyon, and Beach Club landslides. The vote was 3 to 0, with Councilmembers Dave Bradley and Paul Seo absent.
City officials have been directed to consider new alternative methods of slowing the movement, in addition to the hydraugers. Officials also received a report ahead of the expiration, or extension, of the city’s interim urgency ordinance, which is expected to be taken up at the next City Council meeting on Sept. 3.
