Avalanche risk assessment - Ministry of Forests, Lands and Natural ...

The Ministry has responsibility for approving access to subdivisions in
unincorporated areas in British Columbia.; snow avalanches are one of a
number of slope hazards considered in the approval process. The Snow
Avalanche Program has defined a “hazard line” in Stewart, B.C. to delineate
a boundary for potential avalanche influence from Mt. Rainey.
Evacuation of defined areas, including the log sort and port, may be implemented
in extreme avalanche conditions.
Regional Districts in British Columbia
No common approach has been adopted for land use planning in the
regional districts of British Columbia. A zoning system developed in the
Fraser Valley Regional District employs hazard acceptance thresholds for
dealing with snow avalanches and other natural hazards (Cave 1992). The
Fraser Valley Regional District employs a matrix to prescribe responses to
development applications for various types of projects on lands subject to
snow avalanches for a range of annual exceedance probabilities (Table 17).
The column headed “1:500–1:10 000” is considered redundant because it
is impossible to distinguish between that class and the “1:100–1:500” return
period class. The column headed “greater than 1:10 000” defines a
non-restrictive response for areas where avalanche events have not and
will not occur.
The Fraser Valley Regional District has applied the avalanche planning
restriction to projects in the Hemlock Valley area where poorly restocked
clearcuts, harvested in the 1960s, continue to pose an avalanche hazard to
private land downslope. This example underscores the serious implications
that may follow ill-considered clearcut logging on steep slopes that
have the potential to run out into developed areas. The loss in value of
potentially affected residential properties will often outweigh the value
of the timber resource.
Because of the great destructive potential of avalanches and the dread
associated with the phenomenon, the response of the Fraser Valley
Regional District is essentially one of avoidance rather than mitigation.
Interestingly, the planning response to floods, a more familiar hazard,
is less restrictive.
Chapter 3 Avalanche risk assessment 71