Water Stewardship Information Sources
| Citation | Rollerson, T., T. Millard and B. Thomson. 2001. Predicting post-logging landslide activity using terrain attributes: Coast Mountains, British Columbia. Res. Sec., Van. For. Reg., B.C. Min. For., Nanaimo, B.C. Tec. Rep. TR-011/2001. |
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| Organization | FLNRO |
| URL | https://www.for.gov.bc.ca/rco/research/georeports/tr011.pdf |
| Abstract/Description or Keywords | This paper identifies terrain types within the Coast Mountains of British Columbia that were subject to landslides following logging or logging road construction. The study collected field data from 2364 terrain polygons from watersheds primarily located in the southern Coast Mountains. The watersheds were divided into a wetter “Windward Zone” and a drier “Leeward Zone” on the basis of biogeoclimatic zones. Statistical tests were applied to the data set to identify relationships between terrain attributes and landslide occurrence following logging or road construction. Landslides were classified as occurring either in a clearcut or within a road-prism. Overall, the rates of both clearcut- and road-related landslides tend to be much lower in the Coast Mountains study watersheds than have been observed in other areas on the coast. For example, 3.7% of the terrain polygons in the Windward Zone and 1.3% of the terrain polygons in the Leeward Zone experienced clearcut landslides >500 m2 in size. By contrast, 17% of the polygons in study areas on the West Coast of Vancouver Island (Rollerson, Thomson and Millard, 1997) and 22% of the terrain polygons in a study in the Skidegate Plateau in the Queen Charlotte Islands (Rollerson, 1992,) experienced clearcut landslides >500 m2 after logging. Mean clearcut landslide frequencies of 0.012 ls/ha (landslides per hectare) in the Coast Mountains Windward Zone, and 0.008 ls/ha in the Coast Mountains Leeward Zone, are an order of magnitude lower than the Vancouver Island and Queen Charlotte Islands studies at 0.08 ls/ha and 0.17 ls/ha respectively. In common with other studies of post-logging landslides in the Vancouver Forest Region, specific terrain attributes were associated with higher landslide rates. Landslide rates increase as slope steepness increases, except for the very steepest slopes that likely are dominated by bedrock exposures. Increasing landslide rates with increasing slope angle is particularly true for roadfill landslides compared with clearcut landslides. Naturally unstable areas had much higher landslide rates than other areas. Gullies were generally identified as areas subject to high landslide rates, and larger gullies were usually less stable than smaller gullies. The results of these tests can be used to develop classification systems suitable for identifying vulnerable sites before logging and road building occur. |
| Information Type | report |
| Regional Watershed | Lower Fraser, Howe Sound & Sunshine Coast, Central Coast |
| Sub-watershed if known | Nootum, Sheemahant, Machmell, Neechanz, Secutiry, Phillips, Eldred, Lois, Clowhom, McNair, Mamquam, Squamish, Ashlu, Elaho, Meager, Rogers, Scuzzy, American, Bolton, MacKay, Shannon |
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| Contact Name | Tom Millard |
| Contact Email | [email protected] |