6. Impact analysis

The assessment or analysis of impacts is, not surprisingly, at the heart of the EIA process.  Indeed, all other aspects of EIA are designed to facilitate accurate and appropriate undertaking of this task, as well as to disseminate, report and make decisions appropriately based on the outcomes of it.  Therefore, it is perhaps not surprising that this Section is the largest in the Module.  While the practice of assessing impacts is central to impact analysis, there are also important related issues, including wider sustainability dimensions as well as data quality and risk. 

This topic is structured to reflect the three phases of impact analysis that are undertaken as part of the EIA process:

  • identifying more specifically the impacts to be investigated in detail;
  • predicting the characteristics of the main impacts; and
  • evaluating the significance of the residual impacts that cannot be mitigated.

Impact analysis is the technical heart of the EIA process. Depending on requirements, EIA trainers may focus selectively on the above phases, going only into the detail on methods and tools that is appropriate. It is expected that only those groups requiring a comprehensive introduction to impact analysis will work through the whole topic. 

The screening phase of the EIA determines whether or not an EIA is required for a particular proposal. The scoping phase identifies the important issues that should be investigated in detail (making sure that time and money is not wasted investigating issues that are not of concern).

The next stage of the EIA process is when a detailed assessment is undertaken to forecast the characteristics of the main potential impacts. Known as impact analysis, this stage can be broken down into three overlapping phases:

  • identification — to specify the impacts associated with each phase of the project and the activities undertaken;
  • prediction — to forecast the nature, magnitude, extent and duration of the main impacts; and
  • evaluation — to determine the significance of residual impacts i.e. after taking into account how mitigation will reduce a predicted impact.

Impact identification and prediction are undertaken against an environmental baseline, often delineated by selected indices and indicators (e.g. air/water, noise, ecological sensitivity, biodiversity). The collection of baseline information and the relevant biophysical and socio-economic conditions begins during screening and continues in scoping. Often, additional baseline data will need to be collected to establish reference points for impact identification and prediction. These requirements should be identified in the Terms of Reference.

Learning Outcomes of this Section


On successful completion of this Section, you will be able to:

  • Identify and explain environmental impacts and their appropriate assessment
  • Understand and explain impact assessment principles and methods, including the essential difference between magnitude and significance
  • Understand the wider context of environmental impact assessment, including links to the sustainability agenda and social impact assessment
  • Elucidate the problems of data, certainty and risk in impact analysis and how these can be managed.
June 12, 2006 Uncategorized — brendan @ 4:20 pm

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