[Mapping and Assessing Terrain Stability Guidebook Table of Contents]

Appendix 2. Example classification and related criteria for assessing the likelihood of landslide debris entering streamsa

Class

Interpretation

Example criteria

1

  • Low likelihood that a landslide originating in the polygon will enter a stream.
  • The hillslope below the polygon is uniform and the toe of the slope is >100 m from the stream edge.
  • Gully channels within and below the polygon terminate on fans that do not impinge on the stream channel.
  • There is no air-photo or field evidence of landslides entering the stream.

2

  • Moderate likelihood that a landslide originating in the polygon will enter a stream.
  • The hillslope below the polygon is uniform and the toe of the slope is 50-100 m from the stream edge.
  • Gully channels within and below the polygon terminate on fans that impinge on or are partially truncated by the stream channel.
  • There is air-photo or field evidence of limited landslide debris entering the stream.

3

  • High likelihood that a landslide originating in the polygon will enter a stream.
  • The hillslope below the polygon is uniform and the toe of the slope is <50 m from the stream edge.
  • Gully channels within and below the polygon terminate at the streamchannel (there is no fan present).
  • There is clear air-photo or field evidence of landslides entering the stream.

aThis is an example classification developed from experience on Vancouver Island and the Queen Charlotte Islands. Modifications to suit other areas will be necessary. The reader is referred to Benda and Cundy (1990), Church (1983), Hungr et al. (1984), and VanDine (1985 and 1996) for additional background information on landslide runout lengths, deposition zone characteristics and debris yield predictions.


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