Environmental Engineering Reference
In-Depth Information
e.g. humans • Inventories/surveys
• Dose-response factors
( Sources: VROM 1984, Rau & Wooten 1980.)
In practice, there has been a tendency to use the less formal predictive methods, and
especially expert opinion (VROM 1984). Even where more formal methods have been
used, they have tended to be simple, for example the use of photo-montages for visual
impacts, or of simple dilution and steady-state dispersion models for water quality.
However, simple methods need not be inappropriate, especially for early stages in the
EIA process, nor need they be applied uncritically or in a simplistic way. Lee (1987)
provides the following illustration:
(a) a single expert may be asked for a brief, qualitative opinion; or
(b) the expert may also be asked to justify that opinion (i) by verbal or mathematical
description of the relationships he has taken into account and/or (ii) by indicating the
empirical evidence which supports that opinion; or
(c) as in (b), except that opinions are also sought from other experts; or
(d) as in (c), except that the experts are also required to reach a common opinion, with
supporting reasons, qualifications, etc.; or
(e) as in (d), except that the experts are expected to reach a common opinion using an
agreed process of consensus building (e.g. based on “Delphi” techniques (Golden et al.
1979)).
The development of more complex methods can be very time-consuming and expensive,
especially since many of these models are limited to specific environmental components
and physical processes, and may only be justified when a number of relatively similar
projects are proposed. However, notwithstanding the emphasis on the simple informal
methods, there is scope for mathematical simulation models in the prediction stage. Munn
(1979) identifies a number of criteria for situations in which computer-based simulation
or mathematical models would be useful. The following are some of the most relevant:
• the assessment requires the handling of large numbers of simple calculations;
• there are many complex links between the elements of the EIA;
• the affected processes are time-dependent;
• increased definitions of assumptions and elements will be valuable in drawing together
the many disciplines involved in the assessment;
• some or all of the relationships of the assessment can only be defined in terms of
statistical probabilities.
5.2.3 Living with uncertainty
Environmental impact statements often appear more certain in their predictions than they
should. This may reflect a concern not to undermine credibility and/or an unwillingness
to attempt to allow for uncertainty. All predictions have an element of uncertainty, but it
is only in recent years that such uncertainty has begun to be acknowledged in the EIA
process (Beattie 1995, De Jongh 1988). The amended EIA Directive (CEC 1997) and
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