D.7: Predicting Environmental Impacts

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 C.3, D.4, Case Studies 2, 3, 4, & 5 and Appendices 1 - 5, 7 and 8]

SNH's Role

SNH may respond to any requests for advice about the prediction of the environmental effects and predictive techniques or methods that would be appropriate.

Statutory Provisions

SNH's input to the prediction of effects is a non statutory procedure. However, the developer must include the information in the Environmental Statement so this is a necessary procedure for the developer. Guidance on this stage is also provided in PAN 58 at paragraphs 47 - 52.

Impact Prediction

Predicting and describing significant environmental impacts is a statutory requirement to include in an Environmental Statement, reference is made to D.4 above and Appendices 1 - 5 and 7 of this Handbook.

Predicting the effects of a proposed project is a fundamental stage in EIA. One of the main purposes of the Environmental Statement is to clearly explain what the impacts of a proposal would be. The impacts should always be included in the non-technical summary in a way that is understandable to the general public. However, this is not always easy in respect of natural heritage implications.

Predicting natural heritage impacts involves two main elements of work:

Changes are usually referred to as “impacts”.

The effectiveness of impact prediction in Environmental Statements varies considerably. Given the constraints of sometimes inadequate available information, the evolving nature of modeling and predictive techniques, the lack of understanding as to how the natural heritage may respond to some impacts and the extensive reliance of the process on professional judgement, it is not surprising that this element of the EIA process has been widely criticised. Research (25), (26), (27) shows a more rigorous and more impartial assessment of predicted effects in many Environmental Statements since 1992. The trend is one of improvement but some Environmental Statements are still weak in this area.

Box D.7.1
SNH Approach to Impact Prediction

SNH should seek to adopt a practical and rational approach to commenting on the effectiveness of impact prediction. If SNH is unable to support the findings, criticism should be focused on key issues rather than detail. As a minimum SNH should try to ensure that an Environmental Statement fairly and consistently describes

  1. the sensitivity of the natural heritage resource;
  2. the magnitude of change in absolute terms where possible and relative terms elsewhere;
  3. the likelihood of the impacts occurring;
  4. the certainty with which impacts have been identified;
  5. the comparison with the do nothing alternative (see D.8.6 below) and other alternative solutions that are feasible and practical;
  6. the significance of the impacts based on the factors (a) - (d) above (see D.8 below).

Appendices 1 - 5, 7 and 8 of this handbook contain more detailed advice on best practice techniques for predicting impacts and assessing and explaining their significance (see D.8 below). The general principles and main objectives of SNH are set out in this section.

Box D.7.2
Impact Prediction in Casework

Impact prediction will usually require skill, experience and a thorough understanding of the project, the existing conditions and how the environment may respond to change with or without the project. Area staff may often need help from specialist advisers, especially for landscape and visual impacts and impacts on earth heritage features, soils, natural systems, the marine environment and countryside recreation and access.

Different effects may be experienced at different stages in a project's life (eg. site preparation, construction, operation, decommissioning or restoration (See also Figure 4)). The Environmental Statement should clearly set out the effects on the natural heritage and their interrelationships with each other and with other environmental effects.

This will usually require factual information. Prediction of impacts should be as objective and, where possible, as quantified as possible. However, there will often be uncertainties so a range of potential results may need to be considered with an explanation about the nature of the uncertainties associated with predictions.

Box D.7.3
Types of Impact

The effects of a proposal may be:-

  • predictable or unpredictable
  • direct or indirect;
  • positive (beneficial) or negative (harmful);
  • temporary or permanent;
  • short, medium or long-term;
  • one-off, intermittent or continuous;
  • immediate or delayed;
  • certain or uncertain;
  • avoidable or unavoidable;
  • reversible or irreversible;
  • localised or widespread;
  • small or large;
  • individual or cumulative; and therefore
  • significant or of no consequence.

The Information required for impact prediction will generally include:

The magnitude of change should generally be expressed in absolute terms and relatively in terms of percentage change to habitat area or species population or net gains and losses of important landscape features. Given the likelihood of uncertainties, the degree of confidence in the predictions as to the magnitude of effects should also be indicated. The status of the site will generally be a factual expression of the international, national, regional or local importance of landscape, habitats or species. The sensitivity of the landscape, habitats and species will require a professional and sometimes subjective judgement, usually taking account, for example, of the distribution, population, rarity or vulnerability to change of the habitats and species in nature conservation terms and the vulnerability of landscapes to loss of local character or distinctiveness.

By way of example, Figure 5 is an illustration of a matrix showing the magnitude of changes in the landscape. Landscape impact magnitude is based, amongst other things, on the extent of change to the landscape resource, the duration, scale and nature of the change and the impact of the change on the character of the landscape and its tolerance for accommodating change. This is an example only, each EIA will require its own matrix designed to meet the particular circumstances.

Figure 5
Example of Scale of Magnitude of Changes to the Landscape Resource

High magnitude Significant changes, over a significant area, to key characteristics or features or to the landscape's character or distinctiveness for more than 2 years
Medium magnitude Noticeable but not significant changes for more than 2 years or significant changes for more than 6 months but less than 2 years, over a significant area, to key characteristics or features or to the landscape's character or distinctiveness.
Low magnitude Noticeable changes for less than 2 years, significant changes for less than 6 months, or barely discernible changes for any length of time.
No change No predicted changes.

The impacts should be considered in the light of any information available or reasonably obtainable about the capacity of environments to accommodate change. Limits of acceptable change can sometimes be defined and these are particularly relevant to EIA procedures.

Where limits cannot or should not be defined, a broader approach, assessing the capacity of habitats or landscapes to accommodate change, in more general, relative terms could be used. The SNH national programme of Landscape Character Assessments is a particularly important resource contributing to the EIA process. These assessments should be used in every case, and SNH should promote their use as the baseline information for landscape assessment and the most authoritative source of comment on the sensitivity of landscapes, based more on their character and distinctiveness than their designations as such, although designations will need to be considered in the light of their policy implications (see section D.6 above).

Natural Heritage Resource Assessments would also provide authoritative and comprehensive source information relating to the natural heritage resource in an integrated way. These too should be used in EIA to help provide a sound context for the site assessment. (SNH, 1996, Assessing the Natural Heritage Resource Guidance Note for Local Authorities).