Planning in tiers? Tiering as a way of linking SEA and EIA

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; The rivel 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 SEADirective (2001/42/EC) explicitly assumes tiering of SEAs and EIAs at different planning levels and the SEA and EIA Directives are directly linked.