Wind Turbine Visibility and Visual Impact Threshold Distances in ...

It should be noted that average visibility ratings of “1” at shorter distances are almost all
observations made when the wind turbines were shaded, a circumstance that reduces visual
contrast between the turbines and their visual backdrop, or, for the Seven Mile facility, when
views of the facility were partially obstructed.
Summary of Observations with Visibility Rating of “2”
Maximum observed distance: 54.7 km (34.0 mi)
Minimum observed distance: 15.6 km (9.7 mi)
Recommended threshold distance: 48 km (30 mi)
As noted above, a visibility rating of “2” describes facilities that would likely be missed by
casual observers but would be visible when scanning the landscape or looking closely at an area,
without extended viewing. In this study, the maximum distance at which facilities received an
average visibility rating of “2” was 54.7 km (34.0 mi), with another observation at 48.3 km (30.0
mi) receiving an average rating of 2.13. There are five observations with average visibility
ratings of “2” at distances of approximately 45 km (28 mi), and two additional observations with
one rating of “2” between 45 and 47 km (28 and 29 mi), a strong argument that the threshold
should not be set lower than that distance. On the assumption that the longest distance views
might be regarded as exceptional, a more conservative distance for the threshold would be 48
km (30 mi).
Summary of Observations with Visibility Rating of “3”
Maximum observed distance: 36.9 km (22.9 mi)
Minimum observed distance: 12.4 km (7.7 mi)
Recommended threshold distance: 32 km (20 mi)
As noted above, a visibility rating of “3” describes facilities that would be visible after a brief
glance, and unlikely to be missed by a casual observer.” At this level of visibility, impacts may
rise to a moderate level, depending on circumstances and landscape context. In this study, the
maximum distance at which facilities received an average visibility rating of “3” was 36.9 km
(22.9 mi), with several observations receiving ratings of “3” by some observers up to distances
of 50.4 km (31.3 mi). There are four observations with average ratings of “3” at distances
exceeding 32 km (20 mi), and an additional three observations with average ratings of 2.88
beyond 32 km (20 mi). Observations for Seven Mile extended to just under 32 km (20 mi), and
are slightly lower than those for the Cedar Creek facility, possibly because of the mixed
sky/ground backdrop, or possibly because of partially obstructed views. Factoring in the Seven
Mile observations, a very conservative distance estimate for the threshold would be 32 km (20
mi).
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