Environmental impact assessment (EIA) was introduced to inform decision-makers of the potential environmental effects of the decision before them. It has been adopted worldwide and functions as one of the primary instruments for taking account of environmental consequences in project approval decision-making. To date, there has been very little systematic investigation that explores whether the decision-makers for whom the EIA information is produced actually use it, although there are indications that EIA information is not always effective in influencing decisions. This thesis examines how, and indeed if, environmental effects information influences the decision-making processes for which it is produced, and which factors determine the use of this information. Three main areas of concern are identified and investigated: the responses of individual decision-makers to environmental effects information; the characteristics of the effects information that influence these responses; and the processes by which the effects information is dealt with.
At the core of the methodology employed for this research is the development of an exploratory model of EIA-based decision-making. This model builds on the insights into decision processes from a variety of disciplines, including psychology and planning. To test the utility of the model, it is evaluated against the New Zealand system of resource consent approval decision-making under the Resource Management Act, by means of case studies. Through interviews, direct observation, and analysis of written documents the decision processes in these cases are analysed. These techniques have been augmented by psychosocial methods that allow further probing into the decision processes that takes place in a decision-maker's head.
The research results show that the effort that is spent on the preparation of EIA reports and the improvement of EIA processes is not wasted. The EIA information clearly influences the decision processes for which it is intended but it is not influencing decisions optimally. EIA information often competes with information on environmental effects from other sources that is of higher quality, more credible, or better tailored to the decision-makers' information needs. A number of ways in which the use of EIA information could be enhanced is explored in this thesis. Foremost, the improvement of the effectiveness of EIA requires a wider adoption of a decision-making perspective on EIA, and a broader recognition of the information needs of the different decision processes for which EIA is prepared.
