| Summary: | Evaluating investments in projects designed to restore the natural system and prevent
expected loss from events such as landslides is difficult because of the complexity of the
natural system and chance. Using a road deactivation project in coastal British Columbia
as a case study, I demonstrate the use of decision analysis to organize the complexity of
the natural system. The resulting structure provided a series of focal points for an expert
group to develop consensus estimates of the probability of a landslide and the expected
loss for a sample of road segments in the study area. The forest road was segmented by
Terrain Stability Class and divided into 171 road segments approximately one hundred
meters in length. A sample of 17 road sections was used to estimate the relationship
between expected net benefit and road deactivation cost. Cost effectiveness analysis was
used to weigh the expected net benefit of road deactivation with the deactivation cost. The
cost effectiveness analysis showed that cumulative expected net benefit reaches a
maximum then declines as additional road segments are deactivated. As a result there is
a difference between the maximum cumulative expected net benefit and the total
expected net benefit. The results of the cost effectiveness analysis did not significantly
change when the return interval of the rainstorm, the discount rate, and the amount of the
loss due to the landslide were varied.
The results show that it is possible to distinguish between road segments offering high
expected net benefits from road segments offering no expected net benefits. Seventeen
road segments (10% of the 171 road segments) represented 98% ($7,870,000 of
$8,000,000) of the cumulative expected net benefits from road deactivation and 18% of
the cumulative cost ($87,000 of $490,000). Sixty-nine segments (40% of 171 road
segments) had expected net benefit-cost ratios zero and below and represented 39% of
the cumulative cost ($190,000 of $490,000). The results also show that there is a
relationship between road deactivation cost and expected net benefits for Terrain Stability
Classes IV and V. The evaluation approach relied on information that is currently available
including air photographs, contour maps, and road assessments conducted in the field
together with expert opinion. On a larger scale, the approach would be inexpensive to
implement while offering the opportunity to better target the investment of resources,
possibly saving up to seventy or eighty percent of road construction project costs. === Science, Faculty of === Resources, Environment and Sustainability (IRES), Institute for === Graduate
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