Abstract
Abstract. Safe operations of forest practices in mountainous regions require effective development planning to mitigate hazards posed by landslides. British Columbia, Canada, has for the past 2 decades implemented landslide risk management policies aimed at reducing the impacts of the forestry industry on landslides. Consequently, it is required that timber harvesting sites be evaluated for their potential or existing impacts on terrain stability. Statistical landslide susceptibility modelling can enhance this evaluation by geographically highlighting potential hazardous areas. In addition, these statistical models can also improve our understanding of regional landslide controlling factors. The purpose of this research was to explore the regional effects of forest harvesting activities, topography, precipitation and geology on landslides initiated during an extreme rainfall event in November 2006 on Vancouver Island, British Columbia. These effects were analyzed with a nonparametric statistical method, the generalized additive model (GAM). Although topography was the strongest predictor of landslide initiation, low density forest interpreted as regrowth areas and proximity to forest service roads were jointly associated with a 6- to 9-fold increase in the odds of landslide initiation, while accounting for other environmental confounders. This result highlights the importance of continuing proper landslide risk management to control the effects of forest practices on landslide initiation.
Highlights
Landslides triggered by heavy rainfall are a common occurrence on the Pacific coast of British Columbia (BC), Canada
Leave-one-out estimation gave an root-mean-square error (RMSE) of 211 mm and a positive bias of 13 mm, which indicates a slight overestimation of mean precipitation and an acceptable precision considering the high precipitation amounts and large spatial variation
The combined effect of open or semi-open forest cover, interpreted as regrowth areas, and proximity to forest roads was substantial with a 3–4 times increase in the odds of initiation compared to closed forest conditions and distances greater than 50 m from forest service roads, without considering the interaction between precipitation accumulation and forest cover
Summary
Landslides triggered by heavy rainfall are a common occurrence on the Pacific coast of British Columbia (BC), Canada. As regulated by the provincial government of British Columbia, those involved in timber harvesting must ensure that “the primary forest activity does not cause a landslide that has a material adverse effect on forest resource values” (Wise et al, 2004). Timber harvesters are required to provide a “terrain stability hazard map” outlining potentially unstable terrain where landslides may occur. This type of map is often the result of a susceptibility model that predicts the likelihood of landslide occurrence for any given location (Dai et al, 2002)
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