Skip Content

Mitigation, Compensation and Enhancement

Compensation, Mitigation and Monitoring Agreement (CMMA)
Monitoring of Mitigation and Compensation


6.1. During the EcIA process there will come a point when the likely implications of a project are sufficiently well understood to place them in the context of the potential for securing consent for the development. It has to be recognised from the outset that in some instances the impacts may be so severe that it is unlikely that consent will be granted. Ideally this situation should not happen as projects of this type really should not progress as far as detailed EcIA. A broad-scale analysis, in conjunction with dialogue with the SNCOs should screen out such options (see Chapter 2). In other cases, impacts are significant enough to require a package of compensation or mitigation measures to secure a neutral effect on the marine environment. Under certain legislation, such as the Habitats Directive, there is clear separation between avoidance, mitigation and compensation this is described in Box 12. Where a Natura 2000 site is not involved, the terminology is more inter-changeable and therefore for the purposes of this guide we use the broader term ‘offsetting measures’ because the marine environment is less ‘site’-based than terrestrial counterparts.

Box 12:  Mitigation and Compensation – suggested definitions relevant to sites designated under the Habitats and Birds Directives

Mitigation: normally involves measures that reduce and/or minimise impacts within the site boundary such as: changes to timing, engineering design, use of different piling techniques, sediment by-passing to avoid sediment loss or reductions to the extent of a project. However, there will be circumstances where there are impacts that affect mobile species and functionally linked habitats, which may involve measures to address these impacts beyond the boundaries of designated sites. 

Compensation: involves measures, such as new habitat creation, taken beyond the site boundary that offset the residual impacts that have a detrimental impact upon the conservation objectives for a protected site. Compensation is a last resort and should only be considered where there are residual adverse effects on site integrity that the competent authority agrees cannot be mitigated. However, strict tests have to be met before compensation is considered - see paragraph 6.14 for more details.

6.2 Priority should be given to the avoidance of impacts at source, whether through the re-design of a project or by regulating the timing or location of activities. If it is not possible to avoid significant negative impacts, consideration should be given to ways of minimising the impacts by changes to design, timing or working practices, ideally to the point that they are no longer significant. If this is not possible, but the project is permitted, offsetting measures involving some form of habitat restoration or creation may be appropriate, but it should be clear that the levels of success can be very variable. These measures should be designed to meet specific ecological objectives that will deliver measures that specifically address the negative impacts that are predicted. The objectives may include:

  • high level objectives related to the reasons for offsetting impacts, gross area of habitat proposed to be created or restored and its overall quality; and
  • detailed objectives comprising specific ecological requirements for the habitat created or restored in terms of, for example, the number of birds and the habitat attributes that they require.

6.3 Offsetting measures carry a degree of uncertainty. Furthermore, even when they are effective, there may be a temporary or permanent loss of ecological value due to a time lag between damage occurring and new habitats becoming fully functional and/or species becoming established. Forward planning is essential in order to have compensating habitats in place as soon as possible. Follow up monitoring will be required to establish the level of success of compensation.

6.4 Where the success of proposed measures is uncertain or their effectiveness is debateable, evidence should be provided to explain current understanding of their effectiveness and the extent to which their success can be guaranteed. If possible, information from similar projects should be used to support statements about the level of success that can be reasonably expected.

6.5 The uncertainty associated with a project will vary according to a number of factors, including the:

  • technical feasibility of what is proposed (e.g. experience of projects where the proposed mitigation has been employed or carried out);
  • overall quantity of what is proposed (e.g. is it large enough to be viable; is it of at least equivalent extent to that of the lost habitat?);
  • overall quality of what is proposed (e.g. does it compare favourably with features lost and those whose loss or damage is to be compensated?);
  • level of commitment provided to achieve what is proposed (e.g. is there a realistic understanding of what resources and effort will be required to achieve predicted outcomes?); and
  • timescale over which predicted benefits are expected to be realised.

6.6 Offsetting measures should be presented in the context of site integrity or conservation status of the features to which it applies. Evidence should be provided to explain current understanding of their effectiveness and the extent to which their success can be guaranteed, for example, mitigation may be designed to ensure that the status of a species’ population can be maintained following development.

Compensation, Mitigation and Monitoring Agreement (CMMA)

6.7 There is developing experience that the most effective approach to resolving impacts of major projects (i.e. those affecting Natura 2000 sites and likely to be deemed to be necessary for imperative reasons of over-riding public interest) is to involve the statutory agencies and relevant NGOs from a very early stage. This will avoid misunderstandings about how impacts have been identified and facilitate stakeholder collaboration to define measures that might be used to mitigate impacts and any residual impacts that necessitate compensatory measures. This approach, which has been successfully applied to most of the major port developments in England since 2000 (Morris & Gibson 200758), results in a Compensation, Mitigation and Monitoring Agreement (CMMA) that clearly defines the measures that need to be taken if the project is to be consented. This ideally takes the form of a robust, legal agreement that provides certainty for competent authorities and greatly assists the consents process.

6.8 There is also a growing body of opinion (for example guidance in PPS9) that new developments should seek to deliver a net ecological gain rather than simply being designed to only achieve damage limitation and/or like for like replacement.

Monitoring of Mitigation and Compensation

6.9 If offsetting measures are part of planning conditions or obligations, the proponent must implement them fully (see Chapter 6). These conditions or obligations would require a monitoring programme and the implementation of additional remedial measures if the original package of offsetting is shown to have failed to meet its objectives. In the event that this is not a legal requirement it is still good practice to monitor the success of mitigation or compensation measures that are proposed as part of an EcIA, and to remedy the situation should any of the implemented measures fail (e.g. due to lack of management). Given the uncertainties in predicting effects, and the novel nature of some mitigation packages, monitoring is very important. Monitoring should include a robust feedback mechanism to change, or add new, mitigation if effects are greater than predicated. It is also important that such monitoring reports are widely reported and or published to enable the body of understanding to grow in an open a way as possible.

6.10 It is increasingly the view that the potential for enhancement should be addressed in the EcIA. In view of prominence now given to the ‘new agenda for positive planning’, and the guidance referred to in current planning policy, it is important that development is sustainable, and that projects produce a net gain for nature conservation. For example, Planning Policy Wales 2002, section 5.2.7, states that ‘The planning system has an important part to play in meeting biodiversity objectives by promoting approaches to development which create new opportunities to enhance biodiversity, prevent biodiversity losses, or compensate for losses where damage is unavoidable’.

6.11 Therefore, there is often considerable potential not only to mitigate for the adverse impacts of any development, but also to enhance the biodiversity of the development site and its vicinity.

6.12 An Environmental Action Plan (EAP) or CMMA (para 6.7) is an extremely useful means of drawing together the full package of measures and related monitoring. The consents process can be greatly eased by agreement between the relevant parties (proponent, statutory agencies and NGOS) secured by a legal agreement as has been demonstrated by UK port development cases.


6.13 It is often helpful to set out in an EcIA report how a project has evolved in response to ecological considerations and to indicate how mitigation that has been incorporated into the project’s design has enhanced ecological outcomes. Some ecologists present the results of impact assessment 'with' and 'without' mitigation, so that the nature of the mitigation is clearly elucidated. This approach is recommended to increase transparency in the process.

6.14 Where projects affect Natura 2000 sites, the terms mitigation and compensation have very specific meanings. In these situations particular care needs to be taken to make sure that mitigation is confined to those operating procedures that minimise impacts.  Compensation, meanwhile, should be clearly identified as those measures that would have to be delivered to maintain coherence of the Natura 2000 site, if it was determined that:

  1. there would be an adverse affect on site integrity that could not be ruled out;
  2. there were no alternative solutions; and that
  3. there were imperative reasons of over-riding public interest.