Most motorists driving on Pacific Coast Highway between Malibu and Pacific Palisades may have never heard of the Tramonto Drive Landslide.
It exists. If the slope is not fully remediated, the large-scale developments might have unforeseen circumstances: the closure of PCH.
The City of Los Angeles wants to allow a developer to build on the landslide with the idea that by putting in four large homes and swimming pools, it will stop the movement, saving the city the expense of remediating that area.
The City has approved four large houses with pools and basements to be built on the active slide, in the area between Tramonto and Revello. The largest house proposed is 9,051-sq.-ft. with a 5,887-sq.-ft basement, a pool/spa, garage, decks and two retaining walls. Residents have appealed that approval.
The public is invited to attend the West Los Angeles Planning Commission meeting that is scheduled for Wednesday November 15, at 4:30 p.m. at the Palms-Rancho Park Branch Library, 2920 Overland Avenue in the Ray Bradbury Meeting Room click here.
What seems to be missing in planning commission deliberations is a 2010 report from URS Corporation/Caltrans/L.A. City DPW, Bureau of Engineering: “Soil-Structure Interaction Modeling of a Landslide-Stabilization Scheme” that was presented as a proposed stabilization scheme for the Tramonto Drive Landslide.
During a 2009-2019 investigation, there was geologic mapping, borings, downhole geophysics and instrumentation that included monitoring the slide movement specifically in that area.
The report showed a deep-bedrock failure plane between Posetano and Tramonto. That bedrock plane also feeds into the Malibu Bowl earthquake fault.
In that report, it was stated “avoid large-scale grading, use drainage for basic stability and use structural support, which mean excavating to bedrock and deeper with shotcrete and installing hydraugers.” Then the report suggested using solid reinforced concrete to the elevation of the hydraugers.
The report showed that there should be structural-support elements in place besides just excavating to the level of the bedrock.
The cost to reinforce that Tramonto slide area was estimated to be about $25 million in July 2010.
One resident wrote CTN in an email “This developer can’t stabilize the entire slide because they don’t own all the land and probably don’t have the financial resources. I think most of us would welcome a project similar to the one outlined in the 2010 study that would restore all four of the streets (Castellammare, Revello, Stretto, and Tramonto), stabilize the entire landslide, and restore the shoulder of PCH, but that would be expensive; probably two to three times the $25 mil estimated in the 2010 report. If the City did undertake that project, they would recoup some of the cost by selling buildable lots as they did in Portreo Canyon.”
CTN asked Councilmember Traci Park’s Planning and Transportation Deputy Jeff Khau if he had seen the 2010 report and if the Councilmember supported the project.
About the 2010 report he wrote on November 13, “It assumes grading of the entire landslide area, which would be a clear violation of the Coastal Act due to the significant land alterations. For that reason, the report’s proposal is not considered a viable option.”
As far as the Councilwoman supporting the project Khau wrote, “We expect the developer to present a revised project that addresses the issues mentioned (preventing obstructions in the public right-of-way, ensuring that projects are completed expeditiously, and scaling the proposed homes to reflect Castellammare’s existing development pattern) at the WLA APC meeting this Wednesday.
“I want to reiterate that our commitment to ensuring the safety of current and future Castellammare residents is something we take seriously and, while the Councilwoman has not taken a position on the project, whatever stance our office decides to take will be in line with that commitment.”
Castellammare, like many areas in Pacific Palisades, is slide-prone. The toe of the coastal bluff for the proposed project has experienced slope failure in 1982, 1998, 2001 and most recently in 2005.
In 1958, a photo of the homes above the Tramonto slide, taken by the Los Angeles Examiner and housed at the University of Southern California, Roy M. Kirtland, a neighbor, prepares to shoot a picture of “unsafe: home at 17544 Tramonto Drive, Castellammare, (Pacific Palisades). He stands on a sidewalk, part of which has slipped three feet down the hillside. (Interestingly 17544 is one of three addresses with 17538 and 17550 that the developer plans to build.)
In 1958, homes at 17420, 17544 and 17550 were posted (no longer habitable) and Posetano Road, which had dropped about an average of about an inch a day in the last three months, was also closed (Posetano is the road below Revello).
Then, the slide took out the homes directly below Tramonto on Revello Drive and the street itself. One can still see a concrete foundation and bricks from homes that may have been along that street.
Revello is no longer a through street and dead ends on both sides.
“Here’s a house-by-house look at the damage on Castellammare Drive and Porto Marina Way. Castellammare Drive: 17884: Evacuated; extensive side damage; city condemnation process begun. 17885: Some settling and cracking. 17901: Already abandoned as a result of the 1983 and 1989 slides. 17908: Evacuated; severe slide damage; condemnation process begun. 17912: Evacuated; severe slide damage; condemnation process begun. Porto Marina: 17909 and 17919: Threatened by sliding from above; residents ordered to evacuate; condemnation process begun 17945: Separating from foundation; condemnation process begun; residents ordered to evacuate. Other Damage: Porto Marina Way: Broken bulkhead, broken guardrail and extensive slide damage to road in front of 17909 and 17919; a vacant lot across the street from 17919 has essentially vanished; sliding down the hill into the brush and trees above Pacific Coast Highway.”
Severe rains triggered the entire landslide zone from the bulkhead at Tramonto Drive to PCH in 2005. Overnight the entire slope dropped approximately 15 feet, buckling some of the historic concrete stairways in the neighborhood and resulting in the red and yellow tagging of several surrounding homes.