SEA can help to...
1. Identify areas that are environmentally robust and can cope with development; and areas that are environmentally sensitive and where development should be avoided. Typically this is done through overlay mapping, for example:
2. Identify alternatives to a strategic action that are more environmentally sound and/or more sustainable. An example based on the SEA of a UK local transport plan is:
|Based on SEA of UK Local Transport Plan|
|Before SEA||After SEA|
|Draft Plan proposes:||Local Transport Planners also consider:|
|4 major road schemes||fewer road schemes: those that are less sustainable drop out of the plan|
|a £100m road maintenance programme over 5 years||different ratios of expenditure on road maintenance v. walking, cycling and public transport|
|£50m investment in walking, cycling and public transport||different ratios of expenditure between walking, cycling and public transport|
3. Identify a preferred alternative, or reject alternatives. The figure below compares three alternatives (A, B and C) using a range of sustainability criteria. Alternative A is clearly the least sustainable. This was dropped from further consideration, and the plan-making process then focused on various combinations of alternatives B and C.
4. Identify constraints/problems and suggestions ways of dealing with them. For example, urban area X already had little open space (e.g. playing fields, parks). This was restricting people's ability to get informal exercise, and biodiversity was declining. The emerging land use plan was required to accommodate 20% more population within area X over 20 years. This would require more building which would exacerbate pressure on open space, and more people would be using the remaining open space.
The SEA identified this problem. The planners suggested a range of innovative solutions to this problem:
- improved recreational provision at existing open spaces
- rooftop terraces on top of new and existing buildings
- use of the waterfront along adjacent River Y as recreational space
- increased use of River Y for boating, surfing etc.
The SEA showed that existing open spaces and the waterfront could only accommodate a limited amount of additional use; that rooftop terraces were in the private realm and not publicly accessible; and that use of River Y for recreation required a financial outlay (rental or purchase of boat etc.) that many residents of X would not be able to afford.
The final plan also included requirements for new developments to be accompanied by provision of free, publicly accessible open space: 2.5 hectares for every 1000 new residents.
5. Identify mitigation measures to minimise or avoid negative impacts. For instance, for a regional plan in an area where water abstraction already exceeds water supply, a mitigation could be:
"Require all new developments of 10 or more houses to be 'water neutral': total water use in the region after the development must be less than or equal to total water use in the region before the development. For developments of less than 10 houses, water efficiencies of 40% over existing levels must be achieved".
For a local plan that could affect the habitat of a rare bat, a mitigation could be:
"Until more information exists on the foraging habits of the Barbastelle bats at Site Z is available, any development that could affect any trees, hedges or water bodies within 6km of the boundary of Site Z should require assessment to ensure that Barbastelle bat foraging grounds are not negatively affected. If more detailed information becomes available (e.g. if a bat foraging survey is carried out) then this could reduce the need for project level assessment".
The examples above show some typically used SEA techniques:
- maps to describe the baseline environment, identify problems, and predict impacts
- matrices that test alternatives or sub-sections of the strategic action against environmental/sustainability criteria
- use of red/amber/green (traffic light colours) to allow key impacts to be easily identified
- qualitative, +/-, 'expert judgement' type of appraisal where detailed, quantitative assessment is not possible
The last example also represents two typical SEA principles:
- Tiering, as discussed in Unit 3. In this case, in the absence of full information at the plan level, project-level mitigation measures are used.
- The precautionary principle: where there is uncertainty about the impacts of a strategic action, one should assume that negative impacts will occur, and mitigate for them, unless/until one can show that these impacts are unlikely to occur. In this case, all trees and hedges are to be protected until studies show that some of them don't need to be.