Water Stewardship Information Sources

Citation Rollerson, T., T. Millard and B. Thomson. 2002. Using terrain attributes to predict post-logging landslide likelihood on southwestern Vancouver Island. Res. Sec., Van. For. Reg., B.C. Min. For., Nanaimo, B.C. Tec. Rep. TR-015/2002.
Organization FLNRO
URL https://www.for.gov.bc.ca/hfd/library/ffip/Rollerson_T2002.pdf
Abstract/Description or Keywords Terrain attributes are landscape features that can be used to identify
hillslopes susceptible to landslides. For analysis, logged
hillslopes were divided into terrain polygons, which are small
areas that have a consistent set of terrain attributes such as slope
gradient, surficial material type, and slope morphology. Terrain
attribute data was systematically collected in the field in conjunction
with post-logging landslide data and analysed to identify
those terrain attributes that are useful predictors of postlogging
landslides. The method provides quantification of landslide
likelihood ñ an important improvement over qualitative
landslide likelihood evaluation.
Two measures of landslide likelihood were used in this study.
Landslide presence is the presence of one or more landslides within
a terrain polygon. This study analysed landslide presence using
only landslides > 500 m2
in area, as well as the presence of
landslides of any size. Landslide density is the average number of
landslides in a unit area. In this study, only landslides >500 m2
were used to determine landslide density. Three post-logging
landslide types were evaluated: clearcut landslides, road fill landslides,
and road cut landslides. The study used a combination of
univariate and multivariate statistical procedures.
Clearcut areas in the Klanawa, Gordon, San Juan, and Caycuse
watersheds on southwestern Vancouver Island were studied. A
total of 767 terrain polygons was sampled, representing an aggregate
area of 3491 ha. The mean polygon area was 4.6 ha,
with a standard deviation of 3.7 ha and a range of 0.4 to 27.7
hectares. There were 195 clearcut landslides >500 m2
, 228 road
fill landslides >500 m2
, and 47 road cut landslides >500 m2
. A
total of 122 (16%) of the 767 terrain polygons in the sample
population had >500 m2
clearcut landslide presence. Overall, the average
>500 m2
landslide density was 0.06 landslides per hectare (ls/
ha). Of the 567 terrain polygons in the study area with roads,
126 (22%) had >500 m2 road fill landslide presence. Thirty-two (6%)
of the 567 terrain polygons with roads had >500 m2
road cut
landslide presence.
Information Type report
Regional Watershed Vancouver Island South
Sub-watershed if known Klanawa, Gordon, San Juan, Caycuse
Aquifer #
Project status
Contact Name Tom Millard
Contact Email [email protected]