[Mapping and Assessing Terrain Stability Guidebook Table of Contents]

Appendix 1. Terrain stability mapping systems and criteria

Table 1A. Comparison of various terrain stability mapping systems used in BC.

Terrain stability class

Reconnaissance stability class

ESA soil sensitivity class

I

S

unclassified

II

S

unclassified

III

S

unclassified

IV

P

Es2

V

U

Es1

Table 1B. An example of terrain stability class criteria

Terrain stability class

Sample criteria

I

  • floodplains and level to undulating coastal plain areas
  • most terrain with slopes <20%. Exceptions are noted in higher classes

II

  • most gently sloping (20-40%), poorly to well-drained lower slope landforms. Exceptions are noted in higher classes
  • moderately sloping (40-60%), well-to rapidly drained surficial deposits

III

  • moderately sloping (40-60%), imperfectly to poorly drained surficial deposits that are not glaciomarine or glaciolacustrine
  • level to gently sloping (0-40%), imperfectly to poorly drained deep glaciomarine clays and glaciolacustrine deposits
  • moderately sloping, deeply gullied surficial deposits that are not glaciomarine or glaciolacustrine

IV

  • steeply sloping (>60%), well drained, deeply gullied surficial deposits
  • steeply sloping, poorly drained surficial deposits
  • moderately sloping, deeply gullied or imperfectly to poorly drained glaciolacustrine or glaciomarine deposits

V

  • any areas where natural landslide scars are visible on air-photographs or in the field
  • very steeply sloping (>70%), imperfectly to poorly drained, deeply gullied surficial deposits

Caution: These criteria are hypothetical. They do not necessarily represent any particular area in the province. They should not be used as default criteria for terrain stability mapping. Mappers must develop criteria specific to each mapping project based on the historical response of the terrain to timber harvesting and road construction in their map area or similar areas nearby.


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