Landscape hazards for the community of Old Crow are modeled using a Geographic Information System (GIS) to generate an integrated risk ranking for each landscape “unit” (defined by 30m x 30m pixels). Input data for the model include the following datasets: slope; angle (steepness); slope aspect (directionality and exposure to sunlight); and surface materials (derived from the geological map) (see Benkert et al., 2016 for additional details).

Attributes of the individual datasets are classified on a 0-9 scale of potential risk, where zero represents low hazard risk and nine represents high hazard risk. High-risk areas include steep or unstable slopes, low-lying areas subject to flooding or inundation by water, and landscape units with a high likelihood of being affected by ice-rich or thaw-unstable permafrost. Low-risk areas are predicted to have favorable conditions for community development and include well-drained soils, gentle or moderates lopes, and a low likelihood of containing ice-rich or thaw-unstable permafrost.

Each of the input datasets is assigned a unique weighting value in the model that reflects the degree to which they control cumulative hazard risk. For this model, slope angle was given a weighting of 25%. Slope aspect was given a weighting of 15%. Surface materials have a significant impact on landscape stability, and this input dataset was given a weighting of 60%.

Cumulative Ranking = 0.25(slope angle) + 0.15(slope aspect) + 0.6(materials)

By combining the individual rankings of each input raster according to their unique weighting, a cumulative risk ranking for each pixel in the map area is generated. Risk rankings range from 1 (low) to 8 (high). The cumulative rankings are reclassified into four categories (Low, Moderate, Moderately High and High) that represent potential hazard risk due to permafrost, slope stability, and flooding in the map area. The model represents current conditions and does not integrate any potential changes to landscape stability associated with a changing climate.

Low-Risk (green) terrain in the Old Crow area is characterized by flat to gently sloped terrain comprised of well-drained gravel or coarse weathered bedrock surface materials. Low-risk terrain contains permafrost that may be ice-rich, but it is less likely to be affected by flooding and mass movement than more hazardous terrain in the map area. Development is recommended in low-risk terrain.

Moderate-Risk (yellow) terrain in the Old Crow area is characterized by gentle to moderate slopes with moderate to poor drainage. The moderate-risk terrain is found on the pediment slopes of Berry Hill, as well as on poorly drained parts of the fluvial terrace near the North Road (i.e. Site 9) and school (i.e. Site 11) subdivisions. Moderate-risk terrain contains finer-grained material compared to material found in low-risk terrain and is almost always affected by permafrost with high potential for thaw settlement. Development in moderate-risk terrain should proceed with special attention to minimizing impacts on permafrost and existing surface water drainage networks.

Moderately High-Risk (orange) terrain in the Old Crow area is characterized by moderate to steep slopes with all slope aspects. The moderately high-risk terrain is found on the steep escarpment above a town, and in areas subject to regular flooding. Moderately high-risk terrain contains permafrost and is subject to landslides related to poor slope drainage and permafrost thaw. The difference between moderate and moderately high-risk terrain in the study area is largely related to landslide susceptibility. Development should be minimized as much as possible in moderate high-risk terrain.

High-Risk terrain (red) in the Old Crow area is characterized by steep slopes and warm aspects (i.e., west and south facing) with an increased risk of landslides. The high-risk terrain in the study area occurs in areas with documented landslide debris, paths, or features of slow mass movement such as tension cracks. High-risk terrain contains both permafrost and fine-grained surficial materials on steep to very steep slopes that can easily generate landslides with significant run-out distances. Development is not recommended in areas with the high-risk terrain.

Source: www.yukoncollege.yk.ca/research/abstracts/old_crow_landscape_hazards_report

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