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. |
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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 |
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Project status | |
Contact Name | Tom Millard |
Contact Email | [email protected] |