Portuguese Bend Land Movement Geologist Update

Geologist Update

RANCHO PALOS VERDES — At the Aug. 21 Rancho Palos Verdes city council meeting, the city’s geologist, Mike Phipps of Cotton, Shires and Associates, gave an update on the latest land movement data in the Portuguese Bend Landslide complex.

Across 680 acres, the overall rate of movement is leveling off, decelerating by 1% from July to August. Movement ranged from 13% acceleration, to -13% deceleration, depending on location. Generally, movement on the north and west ends of the landslide complex is slowing down, while movement at the south end continues to accelerate, as shown in the map below.

Percent Change in Displacement Rate Map – July-August 2024. Red represents acceleration and green represents deceleration. Click image to open PDF. 

Mr. Phipps called the overall deceleration a “positive sign,” but cautioned that the land is still moving 3.5-4.5 feet per month, about 88 times faster than it was in October 2022. He compared the situation to a car going from accelerating on a freeway to cruising.

Mr. Phipps still does not believe there is risk for a sudden, catastrophic landslide. He also noted that recent data shows the boundaries of the active landslide area have not expanded beyond 680 acres. The city is monitoring the current boundaries of movement for any signs of expansion. 

Watch a recording of the full presentation on the city website. 

Hydraugers Project Update

In June, crews began drilling boreholes in the landslide area as the first step in the city’s project to install two emergency hydraugers — one that will remove water underground contributing to land movement, and another that will intercept water to prevent recharging of groundwater. This test borehole drilling has proven highly beneficial. Samples taken from as deep as approximately 350 feet showed that there is movement on a deeper slide plane in the landslide complex, which had not been previously known. The deeper slide plane is moving much faster than the shallower slide plane targeted by the hydrauger project. 

This new information means city staff and the team of geologists and engineers working to slow the land movement must change their strategy. At last night’s meeting, the council authorized city staff to take a more holistic approach by expanding the project area to encompass the entire landslide complex, prioritizing the deeper slide. 

City staff will return to the council with emergency construction contracts to install deeper, vertical dewatering wells as a pilot program at the toe of the landslide to provide immediate relief from water pressure. Drilling of these wells is expected to begin in the coming weeks. The team will continue to work on developing drainage improvements and assessing the timing of the hydraugers. The city also plans to drill more boreholes throughout the larger landslide area to help the team get a more complete picture of what’s happening underground, as the samples collected to date were isolated to the south end of the Portuguese Bend Landslide.

How to Sign Up for SCE Outage Alerts

On Aug. 19, SCE informed the city of a temporary repair outage in the Seaview neighborhood due to emergency work related to land movement. As a reminder, in the event of a power outage, residents can check sce.com/outage for the latest updates, including an estimated restoration time. Report an outage at sce.com/outage or by calling 1-800-611-1911.

To sign up for outage alerts, go to sce.com/outagealerts. Sign in to your account, click on Profile Settings, and navigate to Contacts for Notifications to add contact information. Then navigate to Preference Center and under Account Preferences, select what notifications you want to receive.

If you have noticed SCE helicopters in the landslide area, note that this is related to ongoing aerial monitoring, as SCE has added the landslide area to its regular route for situational awareness related to landslide activities.

The city will continue to provide regular community updates at rpvca.gov/landmovement. 

Details: For questions, email landmovement@rpvca.gov