During the past fifteen years, environmental impact assessment (EIA) has been, adopted in various parts of the world in order to analyse and mitigate the effects of development proposals. The legislative and institutional frameworks for applying this approach vary considerably among countries and even within federal states, such as the United States and Canada (O’Riordan & Sewell 1981). As a formal procedure, EIA is distinguished by certain characteristics which are common to most, if not all, systems. It is, above all, a predictive exercise directed at the identification and evaluation of the significance of potential changes induced by programmes, projects and activities (see Munn 1979). The emphasis understandably and, perhaps, inevitably is on pre-decision analysis leading to the preparation of an environmental impact statement (EIS) or similar document which establishes terms and conditions for project approval.
The paradox of impact assessment, as conventionally practised, is that relatively little attention is paid to the environmental and social effects which actually occur from development or to the effectiveness of the mitigation and management measures which are adopted. A lack of follow-up after a project has been approved is a major constraint on the advancement of EIA practice (Sadler 1986a). It means that there is no opportunity to learn from and utilize the results of case experience. Yet, learning by trial and error is essential for coping with the uncertainties which characterize complex ecological and social systems (Holling 1978).
An investment in retrospective research can repay major dividends in designing and implementing the adaptive approach to environmental assessment and management, the main currency of international theory and practice (Clark & Munn 1985). The opportunities inherent in this relationship are becoming widely realized. In Canada, for example, EIA audit and evaluation research is under way on several fronts. The directions taken and the findings of selected studies are outlined in this chapter in order to highlight elements of general interest to administrators and practitioners. There are three main objectives. First, the role, scope and contribution of post-decision analysis and