How have we dealt with the need for design flexibility within the assessment of environmental effects?
The ‘Rochdale Envelope’ approach is employed “where the nature of the Proposed Development means that some details of the project have not been confirmed” (for instance the precise dimensions of structures).
Where the details of the Proposed Development cannot be defined precisely, flexibility is sought in alignment with the Rochdale/Design Envelope approach. Flexibility is required in this case as elements of the proposed development are yet to be finalised in terms of choice of technology and for several elements there are options under consideration of which a preferred option is yet to be selected e.g. location of the outfall.
Flexibility is sought in terms of the physical extent of elements that make up the Proposed Development, to allow for optimisation through detailed design whilst providing a level of information sufficient to enable ‘the main,’ or the ‘likely significant’ effects on the environment to be assessed and the mitigation measures to be described. The extent of flexibility in terms of area of land required temporarily or permanently including heights and depths of structures is provided in the plans presented. The scope of assessment assumes a realistic worst case presented in terms of the potential impacts on the relevant receptor or resource. For example, the largest land use change area and disturbance would be assumed for biodiversity matters such as species and habitats whereas the minimum capacity of drainage may be the worst case for assessing the effects of surface water flooding. The assumed realistic worst case is made clear in the information papers which present the likely significant environmental effects both in terms of the geographical extents or areas and durations of potential impacts.