ABSTRACT
The idea of tiering can be considered as one of the major drivers for the development of strategic environmental assessment (SEA) (see, for example, Thérivel et al, 1992; UNECE, 1992; Wood and Djeddour, 1992; Thérivel and Partidário, 1996; Sadler and Verheem, 1996; Partidário, 1999; Fischer, 2002a; Wood, 2003). Many decisions that have a bearing on environmental quality are taken at a higher level of decision-making than the project level. As Partidário (1999, p60) indicates: ‘The reasons [for SEA] are various but initially related to the timing of project [environmental impact assessment] EIA, i.e. it enters the decision-making process at too late a stage to be able the final decision in a satisfactory way.’ Tiering means that, by preparing a sequence of environmental assessments (EAs) at different planning levels and linking them, foreclosure may be prevented, postponement of detailed issues may be permitted and assessments can be better scoped. A tiered approach minimizes the problem of EIA being only a ‘snapshot in time’. Accordingly, the European SEA Directive (2001/42/EC) explicitly assumes tiering of SEAs and EIAs at different planning levels and the SEA and EIA Directives are directly linked.
