Landslide Susceptibility along the Sea to Sky Highway


	Data The data used in this project consisted of Digital Elevation Models (DEMs), road and stream networks, and building and points of interest data. A comprehensive list of the data used is shown below: Road, stream, building, and points of interest data were sourced from Canmap Streets Version 7.2, 2001, DMTI Spatial Inc., refer to http://www.dmtispatial.com for more information. 30m Spatial Resolution DEMs were obtained from the Canadian Digital Elevation Data, Level 1. DEMs provided from this data product are derived from 1:50,000 NTS map sheets. Map sheets 92: G/6, G/7, G/10, G/11, G/14, and G/15 were used for analysis in this project encompassing an area from North Vancouver to Whistler. For more information on the elevation data used refer to http://www.geobase.ca. Methodology Analysis of landslide susceptibility along the Sea to Sky highway conducted in this project is based upon the shallow landsliding model developed by Montgomery and Dietrich (1994). Essentially, two different approaches were used to provide visualization of landslide susceptibility along the Sea to Sky Highway The creation of ordinal maps of slope stability for given friction angles and steady state rainfall rates to produce animations of slope stability with increased rainfall, and for the conduction of areal analysis of slope stability for varied friction angles and steady state rainfall; and The creation of a landslide susceptibility map, and three dimensional visualisation diagrams and animations, based upon the mapping of the critical steady state rainfall required for a slope to transform from a stable to an unstable slope. Detailed methodology for each of these approaches is discussed below. *Creation of Ordinal Maps of Slope Stability* The creation of landslide susceptibility maps which showed areas of stable, unstable, unconditionally stable, and unconditionally unstable land for a given steady state rainfall, and friction angle, was conducted according to the conditions outlined in Figure 1 below. The GIS processes conducted are shown in Flowchart 1, shown below, and were conducted for friction angles of 40 degrees, 45 degrees, and 50 degrees, with steady state rainfall values of 25mm/day, 50mm/day, 75mm/day, 100mm/day, 125mm/day, and 150mm/day for each friction angle. Other parameters used were: soil bulk density = 1800kg/m3, water density = 1000kg/m3, and soil transmissivity = 65m2/day. Figure 1 - Slope Stability Conditions Individual maps of the Lions Bay area were combined using Banner Maker Pro Version 6.0.6 to create animated gif images to visualize the changes in slope stability with varied friction angle and critical steady state rainfall values. Analysis was conducted with a steady state rainfall of up to 150mm/day as, from historical climate data, rainfall in the region generally does not exceed this rate, and also because rainfall rates above 150mm/day essentially transform all stable slopes to unstable slopes, making the model not very useful. The animated gifs produced can be found in the results section or by clicking the following links: Friction Angle: 40 degrees, 45 degrees, 50 degrees Areal analysis of the effects of varying the friction angle on slope stability classes was conducted using Microsoft Excel, and is discussed further in the discussion section of the website. *Creation of a Landslide Susceptibility Map based on Critical Steady State Rainfall* Creation of a landslide susceptibility map showing areas of unconditionally unstable and unconditionally stable land, as well as the critical steady state rainfall required for a stable slope to transform to an unstable slope was conducted according to the conditions outlined in Figure 1 and the model outlined in Figure 2 below. Figure 2 - Slope Stability Model Using the GIS processes outlined in Flowchart 2, detailed slope susceptibility maps of the sea to sky highway from Horseshoe Bay to Squamish were produced with closeups of the Britannia Beach, Porteau, and Lions Bay areas. Additionally, a 3D visualization diagram of Slope Susceptibility for the Lions Bay area was created using ArcScene and Adobe Illustrator, and two flyby animations (#1-56Mb!, #2-65Mb!) of the slope susceptibility overlaid onto a digital elevation model were created using ArcScene. Parameters that were used in the creation of the maps, animations, and diagram were: friction angle = 45 degrees, soil bulk density = 1800kg/m3, water density = 1000kg/m3, and soil transmissivity = 65m2/day. Flowcharts of GIS Processes Conducted
PDF Version Flowchart 1 - Shows GIS processes conducted to create ordinal landslide susceptibility maps for a given friction angle and steady state rainfall rate.	PDF Version Flowchart 2 - Shows GIS processes conducted to create the landslide susceptibility map of required steady state rainfall for slope instability.
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Data

The data used in this project consisted of Digital Elevation Models (DEMs), road and stream networks, and building and points of interest data.
A comprehensive list of the data used is shown below:

Road, stream, building, and points of interest data were sourced from Canmap Streets Version 7.2, 2001, DMTI Spatial Inc., refer to http://www.dmtispatial.com for more information.
30m Spatial Resolution DEMs were obtained from the Canadian Digital Elevation Data, Level 1. DEMs provided from this data product are derived from 1:50,000 NTS map sheets. Map sheets 92: G/6, G/7, G/10, G/11, G/14, and G/15 were used for analysis in this project encompassing an area from North Vancouver to Whistler. For more information on the elevation data used refer to http://www.geobase.ca.

Methodology

Analysis of landslide susceptibility along the Sea to Sky highway conducted in this project is based upon the shallow landsliding model developed by Montgomery and Dietrich (1994). Essentially, two different approaches were used to provide visualization of landslide susceptibility along the Sea to Sky Highway

The creation of ordinal maps of slope stability for given friction angles and steady state rainfall rates to produce animations of slope stability with increased rainfall, and for the conduction of areal analysis of slope stability for varied friction angles and steady state rainfall; and
The creation of a landslide susceptibility map, and three dimensional visualisation diagrams and animations, based upon the mapping of the critical steady state rainfall required for a slope to transform from a stable to an unstable slope.

Detailed methodology for each of these approaches is discussed below.

Creation of Ordinal Maps of Slope Stability

The creation of landslide susceptibility maps which showed areas of stable, unstable, unconditionally stable, and unconditionally unstable land for a given steady state rainfall, and friction angle, was conducted according to the conditions outlined in Figure 1 below. The GIS processes conducted are shown in Flowchart 1, shown below, and were conducted for friction angles of 40 degrees, 45 degrees, and 50 degrees, with steady state rainfall values of 25mm/day, 50mm/day, 75mm/day, 100mm/day, 125mm/day, and 150mm/day for each friction angle. Other parameters used were: soil bulk density = 1800kg/m3, water density = 1000kg/m3, and soil transmissivity = 65m2/day.

Figure 1 - Slope Stability Conditions

Individual maps of the Lions Bay area were combined using Banner Maker Pro Version 6.0.6 to create animated gif images to visualize the changes in slope stability with varied friction angle and critical steady state rainfall values. Analysis was conducted with a steady state rainfall of up to 150mm/day as, from historical climate data, rainfall in the region generally does not exceed this rate, and also because rainfall rates above 150mm/day essentially transform all stable slopes to unstable slopes, making the model not very useful.

The animated gifs produced can be found in the results section or by clicking the following links:
Friction Angle: 40 degrees, 45 degrees, 50 degrees

Areal analysis of the effects of varying the friction angle on slope stability classes was conducted using Microsoft Excel, and is discussed further in the discussion section of the website.

Creation of a Landslide Susceptibility Map based on Critical Steady State Rainfall

Creation of a landslide susceptibility map showing areas of unconditionally unstable and unconditionally stable land, as well as the critical steady state rainfall required for a stable slope to transform to an unstable slope was conducted according to the conditions outlined in Figure 1 and the model outlined in Figure 2 below.

Figure 2 - Slope Stability Model

Using the GIS processes outlined in Flowchart 2, detailed slope susceptibility maps of the sea to sky highway from Horseshoe Bay to Squamish were produced with closeups of the Britannia Beach, Porteau, and Lions Bay areas. Additionally, a 3D visualization diagram of Slope Susceptibility for the Lions Bay area was created using ArcScene and Adobe Illustrator, and two flyby animations (#1-56Mb!, #2-65Mb!) of the slope susceptibility overlaid onto a digital elevation model were created using ArcScene.
Parameters that were used in the creation of the maps, animations, and diagram were: friction angle = 45 degrees, soil bulk density = 1800kg/m3, water density = 1000kg/m3, and soil transmissivity = 65m2/day.

Flowcharts of GIS Processes Conducted

PDF Version

Flowchart 1 - Shows GIS processes conducted to create ordinal landslide susceptibility maps for a given friction angle and steady state rainfall rate.

PDF Version

Flowchart 2 - Shows GIS processes conducted to create the landslide susceptibility map of required steady state rainfall for slope instability.

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