85th AMS Annual Meeting

Monday, 10 January 2005: 1:30 PM
Storminess and coastal change in the Mackenzie-Beaufort region of the Northwest Territories, Canada (Invited Presentation)
Steven M Solomon, Geological Survey of Canada, Dartmouth, NS, Canada; and G. Manson and D. E. Atkinson
Coastal change in the Beaufort-Mackenzie region of the western Canadian Arctic is a product of the interaction between local geological/geomorphological conditions and waves and storm surges driven by winds and modified by sea ice during the open water season. Other aspects of sea ice formation and movement may also play a subordinate role. Examples of coastal changes on scales from several days to decades illustrate the important role of these infrequent, but intense synoptic-scale storms. Recognition of trends in the frequency and intensity of these events is difficult. Similarly, recognition of trends in coastal response can be challenging, especially where detailed time series are not available and temporal aliasing of the process-response relationship occurs.

In a recent study of coastal hazards and hydrocarbon development, aerial photographs from 1972, 1985 and 2000 were analyzed to obtain measurements of coastal change in the Mackenzie Delta region of the Beaufort Sea. Changes from 1972 to 2000 are dominated by retreat of the shoreline with average annual retreat rates of -0.6 m/a, but ranging as high as -22.5 m/a. Rates vary significantly both between and within zones of similar exposure, morphology and coastal geology with the highest average rates located in areas that are most exposed to northwest winds. In general, decadal-scale rates of change have remained constant (1.5 to 2 m/a) along the most rapidly retreating shores during the 28 years encompassed by this study. However, there is a slight (and in some cases statistically significant) tendency towards decreased (20-50%) shoreline retreat rates along the more slowly retreating shorelines during the 1985-2000 period. Simple counts of observed northwest winds greater than 10 m/s during the open water season (July through October) suggest that erosion-producing conditions occurred 1.3 times more frequently during the 1972-1985 period than during the 1985-2000 period. The frequency of winds greater than 15 m/s during 1972-85 was nearly double that of the later period. Insensitivity to storminess at higher rates of shoreline retreat may reflect armouring of coastal bluffs by eroded material accumulated at their base. Analysis of coastal retreat rates at monitoring sites measured more frequently (annually or every 2-3 years) reflect year-to-year variation in storm frequencies, open-water extent, and mean sea levels.

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