Improving the effectiveness of project assessment - Introduction to Environmental Impact Assessment - page 342

• time-crowded perturbations—which occur because perturbations are so close in time
that the effects of one are not dissipated before the next one occurs;
• space-crowded perturbations—when perturbations are so close in space that their effects
overlap;
• synergisms—where different types of perturbation occurring in the same area may
interact to produce qualitatively and quantitatively different responses by the receiving
ecological communities;
• indirect effects—those produced at some time or distance from the initial perturbation,
or by a complex pathway; and
• nibbling—which can include the incremental erosion of a resource until there is a
significant change/it is all used up.
“Cumulative impact assessment is predicting and assessing all other likely existing, past
and reasonably foreseeable future effects on the environment arising from perturbations
which are time-crowded; space-crowded; synergisms; indirect; or, constitute nibbling”
(CEPA 1994). The need to include cumulative impact assessment in EIA has been long
recognized. In the CEQA of 1970, significant impacts are considered to exist if “the
possible effects of a project are individually limited but cumulatively considerable”.
Subsequent legislative reference is found in the 1991 Resource Management Act of New
Zealand, which makes explicit reference to cumulative effects, and now also in the
amended Directive 97/11/EC, which refers to the need to consider the characteristics of
projects having regard to “the cumulation with other projects”. In Canada, which has
been at the forefront in the development of “cumulative effects assessment” (CEA) in
recent years, the consideration of cumulative effects is now explicit and mandatory in
legislation both federally and in several provinces.
However, it is in the practical implementation of the consideration of cumulative
impacts that the problems and deficiencies become clear, and cases of good practice and
useful methodologies have been limited until recently. In Australia, assessments have
largely been carried out by regulatory authorities, rather than by project proponents, and
have focused on regional air quality and the quality and salinity of water in catchment
areas (CEPA 1994). Figure 11.1 provides an example of a simple perturbation impact
model developed by Lane and Associates (1988). It is basically an “impact tree” which
links (a) the principal causes driving a development with, (b) the main perturbations
induced with, (c) the primary biophysical and socio-economic impacts and (d) the
secondary impacts. The figure shows some of the potential cumulative impacts associated
with a number of area-related tourism developments. In the US, the CEQ produced a
practice guide “Considering Cumulative Effects” (CEQ 1997), based on numerous case
studies. The guide consists of 11 steps for CEA, in three main stages.
In Canada, a “Cumulative Effects Assessment Practitioners' Guide” (CEAA 1999)
provides a very useful overview and clarification of terms and fundamentals, of practical
approaches to completing CEAs, and case studies of approaches used by project
proponents. The guide provides some clear and simple definitions—“Cumulative effects
are changes to the environment that are caused by an action in combination with other
past, present and future human actions. A CEA is an assessment of those effects.” Further
Canadian work has sought to improve the practice of CEA (see Baxter et al. 2001). In the
EU, there has also been an attempt to support practice in the area through the
development of “Guidance for the assessment of indirect and cumulative impacts”