Terrain stability mapping on British Columbia forest lands: an historical perspective

Land management associated with forest practices in British Columbia (BC) over the last three decades has led to the development of terrain stability hazard mapping. Terrain stability mapping (TSM) in BC originated in the early 1970s, when forest harvesting was progressing from valley bottoms onto steep, unstable terrain, which led to an increase in harvesting- and road-related landslides. Since then TSM methods have been evolved. Beginning in the early 1970s, terrain hazards were incorporated into the forest inventory classification system to delineate environmentally sensitive areas for land-use planning. By 1974, operational terrain stability maps were introduced by the MacMillan Bloedel forest company on the Queen Charlotte Islands. In the 1980s, this method was adopted by other forest companies and government agencies along the BC coast and then extended to the BC interior in the 1990s. The system was refined over time, based on new knowledge and on the introduction of mapping standards, including standards for capture and presentation of digital maps. In 1995, reconnaissance terrain stability mapping and detailed terrain stability mapping were formalized with three and five hazard classes, respectively. More recently, qualitative and semi-quantitative approaches to predict landslide occurrence based on terrain and landslide inventories have been incorporated into the techniques for TSM.