Wet El Niño Ahead Brings Concerns For Palos Verdes Landslide Complex

RANCHO PALOS VERDES, CA — With weather forecasters predicting a very wet winter ahead with El Niño on the horizon, city officials have already begun planning ways to lessen the impact of rain and surface water at the Portuguese Bend Landslide Complex.

In recent months, city officials have noticed significant movement in the ancient landslide complex in Rancho Palos Verdes that has caused significant roadway damage in the Seaview neighborhood and along Palos Verdes Drive South.

The Palos Verdes Peninsula has seen a huge amount of rainfall since the beginning of 2023, with a total of 20.9 inches of precipitation recorded at the end of March following heavy winter storms and Tropical Storm Hilary hitting in August. Rancho Palos Verdes City Manager Ara Mihranian said the rains have exacerbated the problem.

"For years, dating all the way back to the 70s, all the geologists have been saying we need to address the water," Mihranian said.

The Portuguese Bend Landslide Complex is one of the largest continuously active landslides in the country and is made up of three separate landslides in close proximity to each other. The largest cause of land movement is the water, Mihranian said.

When water gets into the ground, it may take a couple of months for people to see the impacts. Since the 2023 rain storms, city officials have reported water pipe breaks, closed hiking trails and impacted homes and neighborhoods.

Recently, surface water has caused the land to move significantly quicker with engineers saying they have seen essentially a year's worth of movement in just a few months. The city is in the process of developing an Environmental Impact Report that aims to reduce the movement by two inches per year.

"Because of the urgency of everything that has been happening, the city has decided to step in to provide support services," Mihranian said.

According to weather forecasters, El Niño is getting stronger with a 95 percent chance of the storm sticking around through the early months of 2024. Strong El Niño weather patterns are known to bring unusually wet winter seasons, which could spell danger for the ever-moving landslide area.

Historically, Rancho Palos Verdes city officials have installed dewatering wells throughout the landslide complex. These wells are installed vertically and serve the purpose of removing excess water from the ground and water tables and rerouting it into the ocean.

Additionally, the city is currently in the process of installing additional measures at the center of the landslide complex with the Portuguese Bend Landslide Remediation Project. The project plans to install a groundwater extraction system and infill cracks in the ground that let in rain.

Mihranian said officials have been paying close attention to the weather forecasts and the city is working with individual districts to make sure the dewatering wells are in good working condition in preparation for the rain.

"We all need to be working together toward a common solution," Mihranian said.

Recently, Rancho Palos Verdes was awarded a $23.33 million grant to help fund critical improvements needed to slow the Portuguese Bend landslide.

The Portuguese Bend landslide is at the center of the complex that was reactivated in 1956 by Los Angeles County's planned extension of Crenshaw Boulevard, city officials said. The complex has been slowly moving ever since, causing homes to slide by hundreds of feet over the years and costing the city nearly $1 million annually in repairs.

Going forward, city staff proposed a tentative and aggressive timeline for the project that would have the final EIR ready in September 2024 and would have construction on the project begin in late 2025.

Duration of construction could last anywhere from 18 to 24 months depending on the decisions made when finalizing engineering plans, Public Works Director Ramzi Awwad said.