The impact prediction and evaluation stages will have identified the strategic action's significant positive and negative impacts. The impact mitigation stage aims to:
- minimise any negative impacts;
- optimise positive ones;
- enhance sustainability in other ways if possible; and
- ensure that these mitigation measures do not themselves have negative impacts.
A major advantage of SEA over project EIA is that it allows consideration of a wider range of mitigation measures, particularly measures to avoid impacts, at an earlier stage of decision-making. It allows sensitive areas to be avoided and environmentally beneficial developments to be promoted, rather than allowing individual development proposals to be considered on an ad hoc, reactive basis. It may allow some of the potential negative impacts of one action be used positively for another development. It can also allow for a wider range of positive measures to be taken, for instance the creation of new recreation areas or wildlife corridors that go beyond individual development sites.
Strategic level mitigation measures will normally 'look' like changes to the wording and thrust of the strategic action. This could include
- Conditions that permit development only if it is accompanied with specific environmental and community benefits (e.g. a new cycleway, or provision of a percentage of affordable housing).
- Maps showing areas/zones where development is permitted, or excluded, or where only certain types of development are permitted
- Criteria/constraints for lower-tier strategic actions and projects, including 'rules' for implementation and/or requirements for project level EIA. These would particularly useful where the impact prediction stage shows that the impact of a strategic action depends on how it is implemented.
- Specific measures for groups particularly affected by the strategic action, to reduce inequities.
Suggested changes to other strategic actions could also be included, but unless these come with some guarantee that they will be implemented, they cannot really be considered as mitigation measures. The end-result of the mitigation stage should be a list of agreed measures to change the strategic action, change other strategic actions where relevant, and/or set a context for future projects.
The table below shows how mitigation measures and the reasoning behind them can be documented: it is based on an appropriate assessment (a form of cumulative impact assessment - see Unit 10) carried out for the Regional Spatial Strategy for the South East (UK).
|Based on: Appropriate assessment of the UK South East Plan||Proposed Change||Justification|
... Ensure that opportunities and options for sustainable flood management and migration of habitats and species are realised.
|Reflects the first bullets in paras 16.10.1 and 16.11.1 of the AA report.|
Assessment must be undertaken on all proposals in support of the above to ensure compliance with the Habitats Regulations.
|Reflects section 16.6 of the AA report, although widened to ensure assessment of all proposals relating to the policy, not just those at Southampton and Kent International Airports|
||Amendment to (1) reflects section 16.8 of AA report.
Amendment to (2) reflects para 16.8.3 of AA report.
Types of mitigation measures
Mitigation measures are often viewed as a hierarchy:
- avoid the impact altogether
- reduce the magnitude, duration etc. of the impact
- repair the situation post-impact to achieve (more of a) pre-impact state
- compensate for the impact through other means, not necessarily directly related to that impact
- ... and also enhance positive effects where possible.
The higher-level measures are typically cheaper, more politically acceptable, preventive/precautionary, and with fewer social/equity implications than the lower measures. The figure below gives examples.
Mitigation measures can be:
- fiscal, e.g. congestion charging, carbon tax, higher prices for petrol/water/etc., subsidies for environmentally positive behaviour, hypothecation
- regulatory, e.g. building standards, air quality standards, energy efficiency standards for appliances
- educational, e.g. advertisements, leaflets, training courses
- technical/modal, e.g. requirements for a given % of renewable energy production, Sustainable Urban Drainage Systems, wildlife tunnels, bus priority lanes, new infrastructure
- spatial, e.g. density/height of construction, buffer zones, zoning
- further study and assessment during plan implementation, e.g. environmental impact assessment
- positive 'shadow projects', e.g. green infrastructure
For the example above, you may want to consider:
- at what level of the 'mitigation hierarchy' they fall
- whether they are fiscal, regulatory etc.
- whether you can think of any measures that would come higher up on the 'mitigation hierarchy'
Climate change: avoid impacts related to flooding; unclear but probably spatial; can't go higher up the hierarchy
Airports: mitigate impacts during more detailed planning stage; further studies; can the need for new airports and airport expansion be reduced or obviated?
Water resources i: avoid impacts on sensitive sites; further studies; can't go higher up the hierarchy although it might be possible to rewrite the plan so that the plan itself can avoid impacts rather than waiting for lower-level assessment to do so
Water resources ii: reduce water use; technical;avoid water-intensive developments, and/or retrofit existing developments to reduce their water use to balance out the increased water use from new development
What is the difference between alternatives and mitigation measures?
There is no real distinction between alternatives and mitigation measures: a strategic action with mitigation measures is an alternative to a strategic action without such measures. But alternatives are typically broader approaches and mitigation is more detailed fine-tuning; and alternatives typically come earlier, whilst mitigation measures are applied after the preferred alternative (the draft strategic action) is pretty well finalised.