2015 CSCE Annual Conference Regina - Building on our Growth Opportunities Conference
For residential zoning near a snow avalanche path in Canada, three zones are usually identified: Red (no new construction), Blue (restricted development) and White (unrestricted development). The Red-Blue boundary depends on the runout from a 300-year dense snow avalanche. This runout is estimated along the centerline of the path using up to four sources: historical records, trim lines in vegetation, statistical runout models, and dynamic runout models. The confidence and return period for these four estimates vary. Example 1: the extreme trim line in a forested path is of high confidence and typically indicative of a large dense snow avalanche within the last 100 years. The date of the extreme avalanche is known approximately e.g. 60-63 years, but confidence in the return period is only moderate because the trim line is from a single event. Example 2: the statistical runout estimate is typically of moderate confidence and for a return period of approximately 100 years. Traditionally, these estimates with different levels of confidence and return periods are combined with the consultant’s experience. In the proposed approach McClung’s (2005) recently validated Space-Time model is used to adjust the estimates from each of the four sources to a 300-year runout. The 300-year runout for a dense flow avalanche is then calculated as a confidence weighted average, reducing the subjectivity. To compensate for high uncertainty, sometimes because less than four sources are available, the 300-year runout can be extended. Examples are presented to illustrate the proposed method.