The risk of a large landslide roaring down Mount Garibaldi towards the Sea-to-Sky Highway and the northern reaches of Squamish is “unacceptable,” according to a series of engineering reports prepared for the Squamish Nation.
Despite decades of worry at the local level about landslide risk, the reports were brought to public attention in July by a proposal to build a new 700-home subdivision in the area where a landslide is most likely. As a result of the Squamish Nation’s development project, an extensive system of barriers could be built by 2016 to capture a landslide before it could strike the existing community and busy highway.
The reports warn of “significant” economic damage from a landslide that could tower four storeys and smash into the area at nearly 60 kilometres an hour.
Development in the area, known as the Cheekye Fan, is currently prohibited and there are few homeowners living in the possible path of a landslide. However, in late July the First Nation brought its proposal to the local district to build the first phase of the new subdivision.
According to Mayor Rob Kirkham of the District of Squamish, “the risk of landslides has been brought up again and again” in the community, 45 minutes south of Whistler.
New barriers would need to be built before construction could start. If the local council were to accept the Squamish Nation’s proposal, the barriers would also have the added “spinoff” of protecting the Sea-to-Sky Highway and the local airport, according to the mayor.
The economic damage of a landslide blocking the highway to the popular ski resort in Whistler would cost upward of $1-million daily, according to information presented to the council. The damming of the Squamish and Cheakamus Rivers by debris in the case of a landslide could add further costs from significant damage due to flooding.
Two reports prepared for Squamish Nation in 2007 and 2008 by the engineering firm BGC call for the construction of an embankment to guard against the worst landslide expected in a 10,000-year period.
The provincial and federal governments have yet to set rules on how municipalities should judge risk. After a deadly landslide in the District of North Vancouver in 2005, leaders in that area decided to look at risks over a 100,000-year period.
The longer window requires planning for more extreme events.
In the Squamish case, the First Nation’s worst-case scenario would see a landslide carrying 5.5 million cubic metres of materials. That represents the amount of concrete required to build nearly two Hoover Dams.
However, two years after the final engineering study was completed, a rockslide shook Mount Meager 100 kilometres to the north of Squamish, releasing 48 million cubic metres of rubble. That slide was unexpected and the presence of heavy rains blamed for the slide “put into question” some of the limitations in the early study, according to an addendum to the report presented to council in July.
“A slide very similar to the Mount Meager slide is possible in this location as the geotechnical conditions are almost identical,” wrote Chris Lewis, a spokesman for the Squamish Nation.
On March 22, a landslide buried nearly three square kilometres of Oso, Wash., killing 43 people within minutes. That slide, estimated to have contained 7.6 million cubic metres of debris, was similar to what could hit Squamish.
“Protecting our existing assets and our people that reside in this area are the most time sensitive and critical [priorities]. We hope that this development will help us to pay for some of the mitigation costs,” Mr. Lewis wrote.
The First Nation has so far only submitted plans for 150 acres of land it has acquired from the provincial government in the area. An additional 550 acres could be developed. One local councilman has ventured the guess that the barriers could cost upward of $100-million. However, Mr. Kirkham dismissed that estimate as “premature” due to the lack of any final design for the protective infrastructure.
While a panel with representatives from the local district, the Squamish Nation and the province studied the engineering reports before July’s meeting, it was unclear to either Mr. Kirkham or Mr. Lewis who could pay for the full cost of the barriers.