Terrain maps provide information about the distribution and characteristics of surficial materials, landforms, and geological processes in an area. The terrain classification system used for mapping in British Columbia is defined in Howes and Kenk (1988). The Resources Inventory Committee (1994) provides additional important information, including that on terrain survey intensity levels and interpretive products such as slope stability classification. The Mapping and Assessing Terrain Stability Guidebook provides detailed information on the standard procedures to be used for forestry-related purposes in British Columbia.
Terrain mapping and slope stability classification must be done by a registered professional who has extensive experience in terrain mapping and landslide hazard interpretations. Junior mappers can do this work under the close supervision of such an individual.
In British Columbia a five-class slope stability classification is most commonly used. The slope stability classes are as follows:
I. No significant stability problems exist.
II. There is a very low likelihood of landslides following harvesting or road construction.
III. Minor stability problems may develop in some areas.
IV. Terrain polygons contain areas with a moderate likelihood of landslide initiation following harvesting or road construction.
V. Terrain polygons contain areas with a high likelihood of landslide initiation following harvesting or road construction.
Where terrain mapping or slope stability classification is not available for a watershed, the potentially unstable terrain may be assessed as (in order of reliability):
There are a large number of Es1 and Es2 maps in existence that were not produced by such individuals. These are not acceptable for use in IWAP, as there is no certainty that all areas of potentially unstable or unstable terrain have been identified.
Resources Inventory Committee. 1994. Guidelines and Standards to Terrain Geology Mapping in British Columbia. Report prepared for: Terrain Geology Task Group, Earth Science Task Force, Resources Inventory Committee, British Columbia, 1993-1994.