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Forthbank Wind Energy Development
considered to have a limited affect on background sound levels. Inspection of the data
generally tends to support this, given the absence of any identifiable clear data trends that are
normally characteristic of a site affected by rain related background sound levels (such as flat
clusters of data on the noise versus wind plot, or sharp increases in noise followed by a
progressive decrease with time). Notwithstanding this, the possibility exists that some of the
measured background noise data at low wind speeds may have been increased by
extraneous or rain related influences. Time-histories of the noise levels at each survey
location were inspected to look for any atypical relationships when compared to the wind
speeds present during that time. Any elevated levels found in this way were excluded. The
trend of the data when plotted against wind speed was also inspected to look for atypical
relationships or outliers within the data-set which were excluded.
8.3.15 Any data removed from the analysis in the ways described above is indicated on the charts as
red circles, as detailed in Appendix 8.2.
8.3.16 Following removal in particular of rain-affected periods, the range of wind speeds considered
in this analysis was effectively restricted to wind speeds of up to 8m/s. The background noise
is thought likely to generally continue increasing with rising wind speeds, based on experience
of similar environments. Nonetheless, the limits derived in this report have been limited to a
constant value from the highest measured wind speeds. Similarly, when the data trendline
appeared to increase at the lowest wind speeds, the limit was kept constant as this was
considered more representative.
8.3.17 Following the removal of the excluded data points due extraneous noise, the best-fit lines
were generated using a polynomial fit of a maximum of 4 th order. These lines of fit were then
used to derive the noise limits required by ETSU-R-97 that apply during the day-time and
night-time periods up to 12m/s. The corresponding ETSU-R-97 noise limits are summarised in
Tables 8.4 and 8.5. The noise limits have been set either at the prevailing measured
background level plus 5 dB, or at the relevant fixed lower limit, whichever is the greater. The
derivation of the relevant fixed lower limit value used for day-time periods is described in
paragraph 8.2.16.
Table 8.4 Daytime L A90,T Noise Limits (dB) Derived from the Baseline Noise Survey
According to ETSU-R-97
Property
Wind Speed at 10m Height, m/s
3 4 5 6 7 8 9 10 11 12
Park Farm 35.0 35.4 37.5 40.2 43.4 46.9 46.9 46.9 46.9 46.9
Dunmore Home Farm 36.9 38.3 40.8 44.3 48.0 50.1 50.1 50.1 50.1 50.1
13 Riverside View 40.6 42.3 43.9 45.2 46.3 46.9 46.9 46.9 46.9 46.9
Inch of Ferryton 35.0 35.4 37.5 40.2 43.4 46.9 46.9 46.9 46.9 46.9
Craigrie 35.0 35.4 37.5 40.2 43.4 46.9 46.9 46.9 46.9 46.9
Dunmore East 36.9 38.3 40.8 44.3 48.0 50.1 50.1 50.1 50.1 50.1
Dunmore Town 36.9 38.3 40.8 44.3 48.0 50.1 50.1 50.1 50.1 50.1
Bowhouse Gardens 40.6 42.3 43.9 45.2 46.3 46.9 46.9 46.9 46.9 46.9
South Alloa 40.6 42.3 43.9 45.2 46.3 46.9 46.9 46.9 46.9 46.9
12 Riverside View 40.6 42.3 43.9 45.2 46.3 46.9 46.9 46.9 46.9 46.9
November 2010 Chapter 8 Page 10
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