Case studies of EIA in practice - Introduction to Environmental Impact Assessment - page 295

greatest amount of constraint and sensitivity, particularly with respect to visual
impacts, inshore fisheries, marine mammals, birds and offshore habitats of
conservation interest.
• Thames Estuary. Includes areas of low constraint on its eastern boundary, and has fewer
environmental constraints than the other strategic areas. However, several estuaries
and marshes are important bird habitats. Commercial activities (e.g. aggregate
extraction) and recreational navigation are other important constraints.
Risk-based analysis of impacts
For each strategic area, the likely impacts of the two development scenarios (“likely” and
“maximum credible”) were assessed. This analysis incorporated factors that were mapped
as part of the earlier spatial analysis, plus specific receptors that could not be mapped
such as particular bird species. Impacts were quantified wherever possible, or otherwise
described qualitatively, and their significance evaluated using a risk-based approach. This
was based on an assessment of (a) the likelihood of the impact occurring, and (b) the
expected consequences (impact on the receptor). As with the spatial analysis, a scoring
system was used in the evaluation of impact significance, as shown below (DTI 2003a):
Scores for Impact Consequence:
• 5 Serious (e.g. impacts resulting in irreversible or long-term adverse change to key physical
and/or ecological processes; direct loss of rare and endangered habitat or species and/or their
continued persistence and viability);
• 3 Moderate (e.g. impacts resulting in medium-term (5-20 years) adverse change to physical and
ecological processes; direct loss of some habitat (5-20 per cent) crucial for protected species'
continued persistence and viability in the area and/or some mortality of species of
conservation significance);
• 1 Minor (e.g. impacts resulting in short-term adverse change to physical and ecological
processes; temporary disturbance of species; natural restoration within two years requiring
minimal or no intervention);
• 0 None (e.g. impact absorbed by natural environment with no discernible effects; no restoration
or intervention required);
• + Positive (e.g. activity has net beneficial effect resulting in environmental improvement).
Scores for Impact Likelihood:
• 5 Certain (the impact will occur);
• 3 Likely (impact is likely to occur at some point during the wind farm life cycle);
• 1 Unlikely (impact is unlikely to occur, but may occur at some point during wind farm life
cycle).
The impact significance scores for each impact are the product of the consequence and
likelihood scores, ranging from 1 (minor consequence and unlikely) to 25 (serious
consequence and certain).