Environmental Engineering Reference
In-Depth Information
trajectories cross the wind farm without interference and that responses of birds to
all turbine encounters are equal. Mathematically, this can be formulated as:
N * (π * r
2
)/(H * L), where N = number of turbines in a row, r = radius of the
rotor, H = 2r and L = length of a turbine row;
(c) Proportion of birds within vertical reach of rotor-blades at closest range from
the turbines, calculated from the rangefinder data;
(d) Proportion of birds trying to cross the swept area without showing avoidance.
A value of 92 % was derived from Winkelman (
1992
);
(e) Probability of being hit by the rotor-blades. There the wing span, body length
and flight speed was incorporated with information about rotation speed of the
rotor. Biometric measurements were obtained from
http://www.dofbasen.dk/ART/
and flight speeds from Alerstam et al. (
2007
).
The proportion of birds colliding with the blades could then be calculated for
each crossing of a turbine row as: a * b * c * d * e.
Resident Bird Model
The collision risk of resident, local birds was calculated using the modelling frame-
work elaborated by Band (
2012
), which is based on the assumption of multiple
transits through the turbine array by any one individual.
The model requires the following data for the target species and wind farm in
question:
(a) The density of flying birds per km
2
. The densities of flying birds were estimated
from numbers of each species of staging seabirds in the wind farm areas and
three km buffer zones surrounding them. Average numbers of wintering birds of
each species were estimated from aerial surveys. Densities of flying individuals
were then estimated from the total bird density using species-specific proportions
of birds in flight, which have been extracted from the European Seabird at Sea
Database (ESAS v. 4).
(b) Proportion of flying birds within vertical reach of rotor-blades (i.e. potential
'danger zone') was calculated from the rangefinder data.
(c) Daylight hours and nocturnal activity. Nocturnal activity code is entered for
each species, which ranges from one to five and refers to nocturnal activity rela-
tive to the daytime activity of a species. Diurnal/nocturnal activities for selected
species were taken from Furness and Wade (
2012
).
(d) Estimated numbers of birds flying through rotors. Total number of bird transits
through turbines is calculated using the following equation, which combines
the statistics from (b), (c) and (d) and estimates the overall bird flux proportion
of birds flying at risk height:
(
)
(
)
×
2
vD RTRt ft
/ *
2
π
+
Q
A
day
night night
2
R
