Environmental Engineering Reference
In-Depth Information
Collision risk models are used to provide quantitative estimates of potential
mortality arising from collisions with turbines at wind farms. Collision risk models
can be useful when limited information is available to inform potential risk (Madders
and Whitfi eld 2006 ; Strickland et al. 2011 ). In situations where there is insuffi cient
empirical data available to inform risk, collision models may be the only practical
means for its estimation (Strickland et al. 2011 ). Scottish Natural Heritage (SNH)
developed a simple deterministic model implemented in Microsoft Excelâ„¢ to estimate
the probability that a bird fl ying through a rotor would be struck by the turning
blades (also referred to as the 'Band model', Band et al. 2007 ). The Band model is
routinely used to assess avian collision risk at wind farms in the United Kingdom,
and the collision modelling approach is in line with international practice for the
assessment of the risk to birds at wind farms (e.g. Madders and Whitfi eld 2006 ;
Strickland et al. 2011 ). The Band model estimates the probability that a bird of a
given body length, wingspan and fl ight speed fl ying through a rotor is struck by the
turbine blades of given dimensions and operational parameters, e.g. rotation speed.
The model is described with case study examples in Band et al. ( 2007 ). The model
is executed as a three-stage process, i.e. the probability a bird fl ying through the
rotor collides (Stage 1) multiplied by the fl ight rate of birds detected fl ying at rotor
height (Stage 2). The result is then adjusted by multiplying with the proportion of
birds that fail to avoid the turbines (Stage 3).
The model has been mathematically validated by Chamberlain et al. ( 2005 ) who
also provide a cautionary note regarding the use of the model due to its sensitivity
to the rate at which birds may avoid turbines. The sensitivity of collision models
to avoidance rates is further discussed in Chamberlain et al. ( 2006 ). It is worth
noting that avoidance rates are relevant to all collision risk assessments rather
than being unique to the Band model. Additionally, commonly used qualitative or
subjective assessments of collision risk are also subject to the infl uence of
avoidance rates because they necessarily consider that birds generally avoid
collisions with turbines.
Development Envelope and Constraints Mapping - Semi-quantitative
Risk Management Framework
Qualitative risk assessment can provide a rapid and less data complex means of
assessing and managing risk. Qualitative assessments may be more subjective and
should be informed by standards, protocols, rules and regulations, threat or signifi -
cance status or local knowledge. Risk may be assessed by various methods; in our
case study risk was assessed through semi-quantitative habitat mapping within a
proposed development envelope.
A development envelope provides for a development area within which the
respective constraints are identifi ed, detailed and mapped (e.g. constraints map).
These areas are then either avoided or specifi c management is applied to them. The
assumption is therefore that areas within the envelope not identifi ed as signifi cant
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