Landslide Susceptibility along the Sea to Sky Highway


	Introduction The Sea to Sky Highway runs along the east coast of Howe Sound in British Columbia, and connects Vancouver with the cities of Squamish and Whistler. For the most part the Sea to Sky Highway cuts through steep mountainous terrain of the Coast Mountains, along slopes which are subject to periodic landslide events, often as a result of high magnitude rainstorms. *Study Area* The area on which analysis was conducted is defined by the Canadian National Topographic Map Series (NTS), 1:50,000 Maps 92: G/6, G/7, G/10, G/11, G/14, and G/15. This area encompasses towns and cities including Horseshoe Bay, Squamish, North Vancouver, Whistler, Lions Bay, and Britannia Beach. Although analysis was conducted over a relatively large area, the project was focused on the Sea to Sky Highway from Horseshoe Bay to Squamish, which is reflected in the scope of the maps, animations, and diagrams found in the results section of this website. Goals of the Project The goals of this project are to: Analyse the landslide susceptibility for areas surrounding the Sea to Sky Highway from Horseshoe Bay to Squamish, particularly as a result of increased rainfall; and Produce landslide susceptibility maps, animations, and diagrams of the Sea to Sky Highway area to show landslide susceptibility. Background Much of the mountainous coastal landscape of British Columbia is covered with a loose soil mantle of variable thickness, where typically the boundary between the soil and the underlying variably weathered bedrock is abrupt. The soils are commonly rocky, have low bulk density, and lack significant soil cohesion when high in water content. In contrast, the underlying bedrock is commonly fractured and has considerable cohesive and frictional strength. Typically the surface is made up of colluvium and glacial deposits from the quaternary period, which are typically unconsolidated and very unstable, particularly when saturated. The mountainous terrain which lines the Sea to Sky Highway is highly gullied and has very steep slopes, providing favourable conditions for landslide activity. This is a large problem for both users of the heavily traveled highway, and the communities adjacent to the highway. In the past there have been many destructive events that have resulted in the removal of infrastructure and the loss of lives. There are 26 mountain stream basins, which have over 1000 m of relief, that have produced more than 14 landslides in the 25 years up to 1984 (Hungr et al. 1984). From 1981 to 1984 there was a series of five events, which resulted in the loss of life of twelve people, and the destruction or damage of nine bridges and six houses (Hungr et al. 1984) (Refer to Figure 1). Figure 1 - 1983 Debris Flow at Lions Bay (Source: http://www.mala.bc.ca/~earles/howesound/ ) In the fall of 1982, the British Columbia Department of Transportation and Highways initiated a study on landslides, or more specifically, debris flow hazards along the highway. Their goal was to understand the mechanics of the flows and the measures which could be performed to minimize the impacts of the flows (Hungr et al. 1984). At the time there was no methodology to quantitavely analyse aspects of debris flows, thus new techniques were developed to analyse the hazards. Hungr et al. (1984) provides an in depth study into the mechanics of the processes and methods in reconstructing flows. By analysing the aspects of past flows including field measurements of channel width, distinct levees left by the flows, channel shape, and channel length, physical characteristics of flows can be reconstructed (Hungr et al. 1984). In the early 1980's structures were built to catch the debris carried downstream by debris flows in an effort to protect the highway, bridges and the houses which surround the channels (Refer to Figure 2). The reconstructed flows provided evidence of the largest historical flow to determine the amount of debris which a flow could carry down a stream channel, which was important in the determination of the size of the control structure being constructed (Hungr et al 1984). Figure 2 - Harvey Creek Retention Structure, Lions Bay, with Highway 99 at the bottom of the picture (Source: http://www.mala.bc.ca/~earles/howesound/ ) The triggering of these destructive events is largely due to rainfall; as rainfall increases the soil becomes saturated and less stable. The slopes of the Sea to Sky Highway are essentially very unstable due to the large amount of quaternary sediment overlying the bedrock. As this sediment becomes saturated the susceptibility of failure increases. An increase in the frequency of severe rainstorms are one of the possible effects of anthropogenic climate warming. An increase in frequency of severe rainstorms could mean that landslides could potentially become more common along the Sea to Sky Highway, and existing control structures may become ineffective. The primary type of landslide that occurs along the Sea to Sky highway is classified as a debris flow, whereby material is channelized after being triggered, as depicted in Figure 3. Figure 3- Debris Flow Processes (Source: Natural Resources Canada, http://adaptation.nrcan.gc.ca/posters/articles/bc_05_en.asp?Region=bc&Language=en ) Back to the Top Home

Introduction

The Sea to Sky Highway runs along the east coast of Howe Sound in British Columbia, and connects Vancouver with the cities of Squamish and Whistler. For the most part the Sea to Sky Highway cuts through steep mountainous terrain of the Coast Mountains, along slopes which are subject to periodic landslide events, often as a result of high magnitude rainstorms.

Study Area
The area on which analysis was conducted is defined by the Canadian National Topographic Map Series (NTS), 1:50,000 Maps 92: G/6, G/7, G/10, G/11, G/14, and G/15. This area encompasses towns and cities including Horseshoe Bay, Squamish, North Vancouver, Whistler, Lions Bay, and Britannia Beach. Although analysis was conducted over a relatively large area, the project was focused on the Sea to Sky Highway from Horseshoe Bay to Squamish, which is reflected in the scope of the maps, animations, and diagrams found in the results section of this website.

Goals of the Project

The goals of this project are to:

Analyse the landslide susceptibility for areas surrounding the Sea to Sky Highway from Horseshoe Bay to Squamish, particularly as a result of increased rainfall; and
Produce landslide susceptibility maps, animations, and diagrams of the Sea to Sky Highway area to show landslide susceptibility.

Background

Much of the mountainous coastal landscape of British Columbia is covered with a loose soil mantle of variable thickness, where typically the boundary between the soil and the underlying variably weathered bedrock is abrupt. The soils are commonly rocky, have low bulk density, and lack significant soil cohesion when high in water content. In contrast, the underlying bedrock is commonly fractured and has considerable cohesive and frictional strength. Typically the surface is made up of colluvium and glacial deposits from the quaternary period, which are typically unconsolidated and very unstable, particularly when saturated.

The mountainous terrain which lines the Sea to Sky Highway is highly gullied and has very steep slopes, providing favourable conditions for landslide activity. This is a large problem for both users of the heavily traveled highway, and the communities adjacent to the highway. In the past there have been many destructive events that have resulted in the removal of infrastructure and the loss of lives. There are 26 mountain stream basins, which have over 1000 m of relief, that have produced more than 14 landslides in the 25 years up to 1984 (Hungr et al. 1984). From 1981 to 1984 there was a series of five events, which resulted in the loss of life of twelve people, and the destruction or damage of nine bridges and six houses (Hungr et al. 1984) (Refer to Figure 1).

Figure 1 - 1983 Debris Flow at Lions Bay (Source: http://www.mala.bc.ca/~earles/howesound/ )

In the fall of 1982, the British Columbia Department of Transportation and Highways initiated a study on landslides, or more specifically, debris flow hazards along the highway. Their goal was to understand the mechanics of the flows and the measures which could be performed to minimize the impacts of the flows (Hungr et al. 1984). At the time there was no methodology to quantitavely analyse aspects of debris flows, thus new techniques were developed to analyse the hazards. Hungr et al. (1984) provides an in depth study into the mechanics of the processes and methods in reconstructing flows. By analysing the aspects of past flows including field measurements of channel width, distinct levees left by the flows, channel shape, and channel length, physical characteristics of flows can be reconstructed (Hungr et al. 1984).

In the early 1980's structures were built to catch the debris carried downstream by debris flows in an effort to protect the highway, bridges and the houses which surround the channels (Refer to Figure 2). The reconstructed flows provided evidence of the largest historical flow to determine the amount of debris which a flow could carry down a stream channel, which was important in the determination of the size of the control structure being constructed (Hungr et al 1984).

Figure 2 - Harvey Creek Retention Structure, Lions Bay, with Highway 99 at the bottom of the picture
(Source: http://www.mala.bc.ca/~earles/howesound/ )

The triggering of these destructive events is largely due to rainfall; as rainfall increases the soil becomes saturated and less stable. The slopes of the Sea to Sky Highway are essentially very unstable due to the large amount of quaternary sediment overlying the bedrock. As this sediment becomes saturated the susceptibility of failure increases. An increase in the frequency of severe rainstorms are one of the possible effects of anthropogenic climate warming. An increase in frequency of severe rainstorms could mean that landslides could potentially become more common along the Sea to Sky Highway, and existing control structures may become ineffective.

The primary type of landslide that occurs along the Sea to Sky highway is classified as a debris flow, whereby material is channelized after being triggered, as depicted in Figure 3.

Figure 3- Debris Flow Processes (Source: Natural Resources Canada, http://adaptation.nrcan.gc.ca/posters/articles/bc_05_en.asp?Region=bc&Language=en )

Back to the Top

Home