By Shari Faye Dell (published in the West Marin Citizen October 6, 2011)
West Marin Report on KWMR http://kwmr.org/blog/show/749
At a Bolinas Community Public Utility District (BCPUD) meeting in June, the county unveiled plans to reinforce and rebuild the bluff on upper Terrace Avenue, a road that has been closed since January 2010.
Now entering the third week of excavation, on average, 160 truckloads of material are moved daily to a temporary storage site on the soccer field at Mesa Park.
Standing on the rim of the massive pit, spectators speculate, “See those trees over there? They are about 120 feet high, if you stood one of those on the bottom, I bet we would be level with the crown,” says one bystander.
However, appearances can be misleading, according to Marin Department of Public Works Principal Civil Engineer Ernest Klock, the construction crew has nearly reached the target of 135 feet above sea level, or 60 feet below the surface. The goal of this bench excavation, to reach bedrock, will allow access to dig a keyway into the bedrock. This keyway, five to ten feet deep, is the foundational base for layering compacted soil, or soil lifts, between Geogrid fabric, a plastic mesh with very high tensile strength. The layering process continues until ground level is reached, allowing the whole of the repair to act as a unit founded on bedrock. “Advantages to using this kind of repair is that it is very earth friendly,” Klock explained during the June meeting. “We will be using all the existing on-site-materials, no concrete hauling and no mining in southern California for lime to make a concrete retaining wall. The finished surface can be replanted so that it looks exactly like it looked before the slide happened.”
The June estimate of 50,000 cubic yards of material was readjusted just before construction began. Now approaching the adjusted figure of 20,000 cubic yards, the enormous mounds at Mesa Park appear to be at capacity. If the rains let up, excavation goals could be reached with several more days of digging.
Sand, not soil, comprises all but the topsoil removed from the dig. It is because of the sand that the cave in occurred. Standing before a diagram, Klock explains, “The underlying bedrock, this upper sandy mass, is basically sliding on the bedrock. What happens is: rain falls and permeates through that sand, just like on the beach–there is no water build up on the beach, water goes through the sand, hits the bedrock and moves horizontally. So, when all this sandy mass is saturated it tends to slide on the harder material.”
Funding a landslide
Severe erosion at the site drew county attention as early as 2006. Unable to obtain federal funding at that time, Marin County Department of Public Works eventually closed the road to vehicular traffic after storms caused severe slumping in 2010. Additional closures were enforced in April of this year. A cyclone fence was installed around the section that became a deeper, broader pit and signage instructed bicyclists and pedestrians to use an alternate route.
Many locals had grown fond of the auto free zone through the sacred Eucalyptus grove, an annual migration layover to Monarch Butterflies, and the iconic Surfer’s Overlook with the sweeping view of Bolinas’ southern exposed beach, Mount Tamalpais, San Francisco and beyond. While alternative transportation is popular in Bolinas, alternative routes are not: A cliff-side trail allowed locals to sidestep the barricade.
“Funding was always an issue, so until the board allocated funding to fix it, our hands were tied. Being an engineer here, working for the county, I would love to fix everything but money drives all the repairs,” Klock explains. “Basically, after a storm occurs, the engineering division of public works goes out and assesses the damage. Typically, in larger disasters–state of federally recognized disasters–the county receives state or federal aid, but, in this case, we had not. We approached the board, asking for help and they allocated money to fix these high priority slides.”
In conjunction with the County, BCPUD hired a geotechnical engineering firm to explore options to save Surfer’s Overlook from erosion and the immanent failure if left unattended. “Having the known failure at [upper] Terrace and the at risk failure of Surfer’s Overlook threatened accessibility to 41 homes between those two slides,” says Klock. The fact that upper Terrace is an easier, cheaper fix, requiring fewer studies and permits led the county to move forward with repairs.
Bolinians gets a new road and a new field
Where to store one acre of soil ten feet high? That was the question in June but local entities–BCPUD, Bolinas Fire Protection District, and Mesa Park–were able to map out a plan. An agreement was signed, in exchange for resurfacing and reseeding the soccer field at Mesa Park, otherwise known as the Firehouse Park, use of the field was granted through December.
Bolinas Fire Chief Anita Brown describes safety concerns that can soon be dismissed.
“I am very happy that the counthy has undertaken this project being that the majority of our residents live on the mesa and being that mesa road which is now the only road on and off the Mesa, has been close twice this year. That means no one can get downtown and because the firehouse is on the Mesa, we can’t get fire engines downtown. We can’t get an ambulance up to residents on the Mesa, so the fact that the county is doing this is a great project. We need both access roads.
Gavi Emunah, a seventh grader at Bolinas-Stinson School says, “Terrace is a safe place to ride bikes and skateboards and it is nice to walk down a road with a view and without cars.”
“I feel that could have built a short road through the sewer ponds or the quail preserve with eminent domain, routing traffic from Overlook to Marin Way,” says Albert Hollander, a Bolinas resident since 1973. “Then Terrace could be a walking street. The main reason they are doing the repair is so people on Marin Way can have access if Surfer’s Overlook fails. I, however, have a home at the foot of terrace. I have enjoyed the street being closed. It has reduced traffic and fumes that I experience from the constant flow of traffic. Other people also express their joy at walking unencumbered by automobiles. The road is dangerous–narrow and there is no soft shoulder.”
On the edge
Early last week the house on the southeast corner of Overlook and Terrace avenue still had a picket fence and yard. The house is now perched five feet from the precipice after loosing twenty feet of yard to fall in around the dig.
“The contractor is responsible for that damage. We had no intention of going onto private property with the repair, that was the result of the sands being loose in that area and the contractors operation caused that,” says DPW’s Ernest Klock. “So, Maggiora & Ghilotti is on the hook for that. They are in contact with the property owner and working with them.”
In briefest form, this story can be he heard at kwmr.org/news