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1.1 What is environmental impact assessment?

Essentially, environmental impact assessment (EIA) is an environmental decision support tool, which provides information on the likely impacts of development projects to those who take the decision as to whether the project should be authorised. The purpose of an EIA is to determine the potential environmental, social, and health effects of a proposed development, so that those who take the decisions in developing the project and in authorising the project are informed about the likely consequences of their decisions before they take those decisions and are thereby more accountable. It is intended to facilitate informed and transparent decision-making while seeking to avoid, reduce or mitigate potential adverse impacts through the consideration of alternative options, sites or processes.

EIA forms part of the spectrum of environmental assessment (EA) processes. Whilst EIA relates to specific projects, EA is a generic term, which also incorporates strategic environmental assessment (SEA) of policies, plans, and programmes, and other forms of assessment. The distinction between these processes is highlighted in the definitions provided below.


There are a number of definitions of environmental assessment, EIA and SEA. Just a sample is given here.

Environmental Impact Assessment (EIA) is a systematic and integrative process for considering possible impacts prior to a decision being taken on whether or not a proposal should be given approval to proceed (Wood 2003)

Strategic Environmental Assessment (SEA) is a process of prior examination and appraisal of policies, plans, and programmes and other higher level or pre-project initiatives (Sadler 1996)

It is important to note that the terms defined above have differing interpretations and meanings in different countries, and that EIA and EA are often used interchangeably. In the UK, for example, the term EA has often been used to describe project-level assessment. However, for the purposes of this unit the definitions and distinctions introduced above are used.

The objective of EIA is not to force decision-makers to adopt the least environmentally damaging alternative, but rather to make explicit the environmental impact of the development, so that the environment is taken into account in decision-making. EIA has been regarded as both a science and an art, reflecting the technical aspects, such as impact identification and prediction, as well as the evaluation, management, and presentation of information. Before looking at EIA in more detail, it is worth looking at the nature of environmental change that needs to be considered to provide a context.