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