Published on June 19th, 2012 | by RLn Staff1
White Point Slide Report Affirms Natural Causes for Slide
By Terelle Jerricks, Managing Editor
On June 18, an engineering report affirmed that the White Point slide, which took place in December 2010, was the result of erosion and not of any one particular factor.
Another morsel taken from the hour-and-half long meeting: neighborhood residents are about evenly divided on what to do about Paseo del Mar, the street marred by a huge hole in the ground.
Councilman Joe Buscaino scheduled the community that included city engineer Gary Lee Moore and others from his office to discuss the long-awaited report that was only put online the following morning.
Moore talked about the 800-page report, focusing on the maps that used data collected from dozens of monitors and core samples, and turning the community meetings into a lecture on geology and soil erosion mixed with a bit of humor.
Moore presented on multi-colored maps depicting the site of the slide, historic slide areas and dormant areas, as well before and after photos of the slide area. Shannon and Wilson Inc., the consulting firm hired to study the slide site, drilled core samples 100 feet into the ground and sent a camera through the holes and other instruments to gather data on what direction if any the ground was moving.
“All the reading since December shows virtually no movement in any of the shafts sites,” Moore said.
Moore explained that water and gravity were important variables causing the slide. He said that the soil in the western part of the site was saturated with water. At the same time, the consultants couldn’t point leaky sewer lines, broken water pipes, or excessive irrigation as the cause of the extra water, except to note there was some extra rain.
“From December to May, we’ve seen an increase in groundwater,” Moore said. “We want to know if it’ll go down over the summer. It was 15 feet higher now than in December.”
Moore then focused on the sediment on the site and noted that the report’s authors didn’t detect movement through that analysis either.
“Before the land moved, alta mira shell was predominant soil and bentonite clay,” Moore said. “Clay is very slippery. With the modeling done by the consulting team, the top area was filled with water and gravity caused the slide.”
The report states that not any one reason was the cause, but all were contributing factors.
According to the report, there were no utilities, or irrigation on the nature preserve and Nike missile base was ruled out as a cause by the city-hired consulting firm.
In the meantime, the city plans to install more monitoring wells and drainage ditches to remove excess water. This in addition to cleaning up the area by getting rid of the storm pipe and the broken pieces of asphalt falling into the ocean. There was also discussion of installing a slope anchor system to reinforce the slide area as well as make traffic improvements to ease traffic and speeding.
Earlier on June 18, Rep. Janice Hahn sent a letter to Col. Mark Toy of the U.S. Army Corps of Engineers to seek federal assistance in recovery and prevention efforts, a follow to his invitation to the slide area in April 1. At the time he said the only way the Army Corp of Engineers could get involved is if it was found that the slide was the result of long-term coastal bluff erosion.
“I’m calling on the Corps to provide its expertise in strengthening the bluff to prevent a future landslide,” Hahn wrote in the letter. “When we toured the landslide earlier this year, you indicated that the U.S. Army Corps of Engineers could become engaged – and there could be potential federal funding — in the landslide recovery and prevention efforts if coastal erosion was determined to be a cause of the landslide.”
For the long term, discussions revolved around four different options:
- Installing earth anchors that a bolted from the beach side on Weymouth and Paseo del mar. Officials said it shouldn’t be too aesthetically intrusive.
- Abandon the roadway is an option save $1 million. (already spent $7 million on studies and fences)
- Grade the roadway and put in a dip like Portuguese Bend. The drawback is high maintenance costs. The possible solution would cost $50 million.
- Restore the road supported by a retaining wall. The cost is $27 million.
- Building a bridge over the hole would be the most expensive option at $60million.
Rerouting the road across the Nature Preserve would be problematic only because the road could only be open during the hours that the park was open, which closes at 10 p.m. Moore noted that the park since the park is owned by Recreation and Parks, the Nature Preserve can’t be used for anything other than parks, a statement that came with great applause.
Moore joke that they could just paved the road into the worlds largest asphalt ramp that dips into the hole for skateboarders.
A draft of the final geo-technical report can be viewed at eng.lacity.org/whitepoint/whitepointlandslide.htm