RPV: Future Landslide Concerns

Recent landslides resulting in single family home properties being red-tagged have caused concerns for future landslides with the approaching winter rains and potential “el nino” events, potentially bringing even more rain than usual.

Back in July, Rolling Hills experienced a landslide resulting in 12 homes experiencing significant damage and ultimately being red-tagged. The cause of the landslide has yet to be officially announced, but given the evidence from residents, the likely cause may have been a water line leak.

In June and August, two homes in Rancho Palos Verdes (RPV) near Portuguese Bend were also red-tagged due to land movement, and again a water leak is the primary suspect. Although the events were unrelated, the culprit was likely a broken water pipe. But how the pipe was broken is the question at hand.

RPV is known for having areas with constant land movement, which has occurred for decades, and can be seen in action when driving through Portuguese Bend on Palos Verdes Dr South. The land in that area is under constant movement, as described on the City’s website:

Reactivated landslides within the greater Ancient Altamira Landslide Complex, which encompasses over two of the City’s roughly fourteen square miles, move at rates between hundredths of an inch per year and tens of feet per year. This movement is especially noticed by motorists, cyclists and pedestrians who travel along Palos Verdes Drive South. Furthermore, they present a challenge to City Public Works staff who are tasked with maintaining safe access through this area. Portions of the landslide have been incorporated into Geologic Hazard Abatement Districts, in which the City participates as a land owner. These districts work to slow land movement through both policy and physical solutions. Elimination of septic systems, installation of dewatering wells, and control of storm water are some of the measures used.

In addition, the City works hard to maintain a safe roadway through the area at a cost of about a half million dollars per year. Regular travelers through the area are familiar with the frequent need to repair cracks and smooth out the roadway. The costs to “stop” the land from moving are incalculable, even if the technology existed to make that happen. Since it does not, the City does its best to “manage” our activity in the face of the nature’s processes that are indeed very real.

https://www.rpvca.gov/719/Landslide-Management-Program

Knowing this, could the water main breaks in Rolling Hills and RPV have been caused by land movement initially, which then resulted in rapid destabilization of the foundations? With the wetter-than-usual winter we had last year, plenty of water was introduced into the soil. This rainfall can take a long time to affect the terrain, according to the City’s website:

Increased movement has been observed elsewhere within the City’s landslide complex, including the Portuguese Bend Landslide particularly in the Portuguese Bend Reserve, a subarea of the City’s Palos Verdes Nature Preserve. All the recent movement is believed to be primarily the result of heavy winter rainfall resulting in surface water percolating into the ground and lubricating the bentonite soil condition, since it can take anywhere from a few weeks to a few months after the rainfall for the land to move. Water pipe leaks, especially when undetected for an extended period of time, may be exacerbating the accelerated land movement in the area. Please note there is no link between this activity and the devastating land movement that destroyed homes in the City of Rolling Hills Estates this summer. 

City of RPV Website

Many residents near the RPV red-tagged homes claimed the water company was not responding quickly enough to reports of water leaks, leading to more damage and loss of property. As of now, no evacuations have been announced, but concerns of more land destabilization on the PV peninsula remain high as we head towards another wet winter.

The water company, California Water Service, is doing its part in addressing the situation and has created a webpage to keep the community updated

Visit RPV’s Land Movement page for more info.

UPDATE from RPV Site: State of emergency declared due to land movement:

The City of Rancho Palos Verdes is closely monitoring land movement in the Portuguese Bend, Abalone Cove, and Klondike Canyon landslides that has accelerated in recent months. No evacuation warnings or orders have been issued at this time for the neighborhoods in and adjacent to the landslide complex. There are steps residents in the zones highlighted below can take to be prepared, should the situation change in the future.

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