D.9: Mitigating Measures and Enhancement

Key Stages and Steps in the EIA Process
Stage 1: Before Submission of the Environmental Statement
  • Deciding whether EIA is required
  • Requiring submission of an Environmental Statement
  • Preliminary Contacts and Liaison
  • Scoping the Environmental Statement
  • Information Collection
  • Describing Baseline Environmental Information
  • Predicting Environmental Impacts
  • Assessing the Significance of Impacts
  • Mitigation Measures and Enhancement
  • Presenting Environmental Information in the Environmental Statement
Stage 2: Submission of Environmental Statement and Consideration of Environmental Information
  • Submission of Environmental Statement and Project Application for consent
  • Consultation and Publicity
  • Requiring more Information
  • Negotiating modifications to the Project
  • Considering the Environmental Information
Stage 3: Making the Decision
  • Making the Decision
  • Guaranteeing compliance
Stage 4: Implementation
  • Implementation of mitigation and compensation measures
  • Monitoring
  • Review, reassessment and remedial measures
  • Reporting

[See Also Figure 2, Sections B.6, D.4, E.7, E.10 and F.2, Case Studies 1, 3 and 4 and Appendices 1-8]

SNH's Role

SNH may advise the developer or the Competent Authority on mitigation and may negotiate measures to avoid, reduce or compensate effects on the natural heritage and opportunities for enhancement.

Statutory Provisions

The Environmental Statement must include a description of the mitigation measures, so this is a necessary procedure for the developer. It will also be a necessary procedure for SNH to consider the effectiveness of mitigation in order to make representations to the Competent Authority.

Mitigation measures are a statutory requirement to include in an Environmental Statement, enhancement is not, reference is made to B.6, D.4 above and Appendices 1 - 5 and 7 - 8 of this Handbook. Guidance on this stage is also provided in PAN 58 at paragraphs 53 - 61. Note also the specific meanings attached to "mitigation" and "compensatory measures" by SNH in case work affecting Natura 2000 Sites, see "Glossary of Key Terms in Birds and Habitats Directives and the Conservation (Natural Habitats &c) Regulations 1994."


One of the main purposes of EIA is to ensure that potentially significant environmental effects of proposed projects are avoided or reduced as far as possible or practicable. This can be achieved by many different measures which might include:-

In the EIA process it will be necessary to consider four distinct treatments of the project and its environmental effects as follows:

These distinctions are not merely of academic interest. For the purposes of the EIA Regulations, SNH will refer to ‘mitigation measures’ as including Avoidance, Reduction and Remedy / Compensation. These must, therefore, be included and described in every Environmental Statement (see sections B.6 and D.4 above). However, for the purposes of the Habitats Regulations, in respect of regulations 48 and 53, in Natura 2000 site case work, when addressing competent authorities and developers, SNH should refer to the terms "mitigation" and "compensatory measures" consistently with the "Glossary of Key Terms in Birds and Habitats Directives and the Conservation (Natural Habitats &c) Regulations 1994." In Natura 2000 case work, a distinction needs to be made between mitigation measures (which are taken into account in the regulation 48 appropriate assessment) and compensatory measures, which are not taken into account in the regulation 48 appropriate assessment, but are considered in regulation 53, if the project may have an adverse effect on the integrity of a Natura 2000 site but there are no alternative solutions and it must be carried out for imperative reasons of overriding public interest.

Enhancement, or net benefit, or new benefit, may be offered by the developer. Often an Environmental Statement has claimed enhancement but the measures are not genuine enhancement because the loss or damage to the natural heritage is greater than the benefit of the “enhancement” proposed or the measures are more akin to compensatory measures.

In any event, competent authorities need to distinguish between mitigating measures and enhancement to clearly understand the effectiveness of the mitigation.

Box D.9.1
Mitigation and Enhancement

Mitigating measures or mitigation are the measures taken to avoid, reduce or remedy adverse impacts of the project.

Avoidance is the measures taken to avoid any adverse impacts, including alternative or ‘do nothing’ options.

Reduction is the measures taken to reduce unavoidable adverse impacts of the project.

Remedy or Compensatory measures or compensation are other measures taken to (at least try to) offset or compensate for residual adverse effects which cannot be avoided or further reduced.

Enhancement / Net Benefit / New Benefit is the genuine enhancement of the natural heritage interest of a site or area because adverse effects are limited in scope and scale, and the project includes improved management or new habitats or features, which are better than the prospective management, or the habitats or features present there now. There is, therefore, a net or new benefit to the natural heritage.

The distinction is also relevant to SNH. For example, a project may result in adverse ecological effects, on existing habitats, that cannot be mitigated, eg. loss of an important peatland area but may also result in genuine landscape enhancement elsewhere. The one is not a compensation for the other. The loss and the benefit must be weighed as separate issues. Likewise, a Competent Authority may need to weigh the significance of harm to the natural heritage perhaps with enhancement of other environmental conditions.

Developers are entitled to include environmental enhancement in their Environmental Statement. Whilst most Environmental Statements tend to focus on mitigation, developers may perceive an opportunity to help to persuade a Competent Authority to grant consent by offering some form of enhancement, to tip the balance in favour of the project.

In many cases there will be opportunities to encourage enhancement of the natural heritage, especially where the existing ecological interest is low or a landscape has been degraded. Mineral or waste restoration schemes and woodland planting schemes often offer potential for genuine enhancement where the harm to the natural heritage is insignificant.

Box D.9.2
SNH Approach to Mitigation

Generally, SNH should promote a sustainable approach and give priority to:

  • firstly avoiding adverse impacts on the natural heritage; then
  • reducing unavoidable adverse effects on the natural heritage; then
  • compensating for the adverse effects that cannot be further reduced; and
  • in parallel with this prioritised approach to mitigation, encouraging opportunities to enhance the natural heritage

However, it should be borne in mind that enhancement cannot be insisted upon. Whilst the SNH comments on the Environmental Statement and the letter making representations about the project itself are separate things, the representations will be informed and supplemented by the comments on the Statement. When responding to the consultation and expressing SNH's views about the development, it is legitimate for SNH to press for the maximum possible mitigation and to object to a proposal that is not mitigated to the extent that would be feasible and practical (even if the project, in principle, is acceptable). It would not be appropriate to object on the grounds that a scheme did not include enhancement. Under all of the relevant decision making processes that involve EIA, the developer can only reasonably be expected to mitigate the effects of a project, not to enhance the resource. See also sections E.10 and F.2.

It is important to consider the effects on the natural heritage of the mitigation measures themselves and to reassess the impacts when new or different measures are introduced by the developer or Competent Authority during negotiations about the proposal.

Mitigating measures should not be afterthoughts or measures introduced at final design stage merely to offset the most obvious environmental impacts. Mitigation should be a continuous, iterative process throughout the life of the project. Each of the stages of the project may require different mitigating measures.

The effectiveness of mitigating measures, their reliability and certainty, and the commitment to ensuring their practical implementation should be addressed in the Environmental Statement (See Section F.3). The environmental effects of mitigating measures themselves should also be assessed. Measures may have been added at a late stage and may not have been assessed in the Environmental Statement. The measures themselves may have significant natural heritage effects, for example through further habitat loss or by the obstruction of wildlife corridors or intrusion into the landscape or obstruction of views.

The effectiveness of measures such as habitat recreation, restoration, revegetation or habitat or species translocation should be considered on their merits in the circumstances of each case. However, bearing in mind the general experience of habitat and species translocation, this should normally be regarded as a last resort when destruction of individuals of the species is inevitable, that is, a rescue operation.