Introduction and principles - Introduction to Environmental Impact Assessment - page 22

reservoir based on a river system not only takes land for the immediate body of water but
also may have severe downstream implications for flora and fauna and for human
activities such as fishing and sailing.
The direct and indirect impacts may sometimes correlate with short-run and longrun
impacts. For some impacts the distinction between short-run and long-run may also relate
to the distinction between a project's construction and its operational stage; however,
other construction-stage impacts, such as change in land use, are much more permanent.
Impacts also have a spatial dimension. One distinction is between local and strategic, the
latter covering impacts on areas beyond the immediate locality. These are often regional,
but may sometimes be of national or even international significance.
Environmental resources cannot always be replaced; once destroyed, some may be lost
for ever. The distinction between reversible and irreversible impacts is a very important
one, and the irreversible impacts, not susceptible to mitigation, can constitute particular
significant impacts in an EIA. It may be possible to replace, compensate for or
reconstruct a lost resource in some cases, but substitutions are rarely ideal. The loss of a
resource may become more serious later, and valuations need to allow for this. Some
impacts can be quantified, others are less tangible. The latter should not be ignored. Nor
should the distributional impacts of a proposed development be ignored. Impacts do not
fall evenly on affected parties and areas. Although a particular project may be assessed as
bringing a general benefit, some groups and/or geographical areas may be receiving most
of any adverse effects, the main benefits going to others elsewhere. There is also a
distinction between actual and perceived impacts. Subjective perceptions of impacts may
significantly influence the responses and decisions of people towards a proposed
development. They constitute an important source of information, to be considered
alongside more objective predictions of impacts. Finally, all impacts should be compared
with the “do-nothing” situation, and the state of the environment predicted without the
project. This can be widened to include comparisons with anticipated impacts from
alternative development scenarios for an area.
We conclude on a semantic point: the words “impact” and “effect” are widely used in
the literature and legislation on EIA, but it is not always clear whether they are
interchangeable or should be used only for specifically different meanings. In the United
States, the regulations for implementing the National Environmental Policy Act (NEPA)
expressly state that “effects and impacts as used in these regulations are synonymous”.
This interpretation is widespread, and is adopted in this text. But there are other
interpretations relating to timing and to value judgements. Catlow & Thirlwall (1976)
make a distinction between effects which are “…the physical and natural changes
resulting, directly or indirectly, from development” and impacts which are “…the
consequences or end products of those effects represented by attributes of the
environment on which we can place an objective or subjective value”. In contrast, an
Australian study (CEPA 1994) reverses the arguments, claiming that “there does seem to
be greater logic in thinking of an impact resulting in an effect, rather than the other way
round”. Other commentators have introduced the concept of value judgement into the
differentiation. Preston & Bedford (1988) state that “the use of the term 'impacts'
connotes a value judgement”. This view is supported by Stakhiv (1988), who sees a
distinction between “scientific assessment of facts (effects), and the evaluation of the