Article 12

12.1.5 Environmental impact assessment

Environmental impact assessments (EIAs) are an important element of the planning process by which environmental considerations are integrated into decision-making procedures for measures that may have adverse (environmental) effects.275 The overall aim of an EIA is to provide a basis by which to come to an informed decision through a thorough analysis of anticipated environmental impacts – revealing the main risks of the project and providing pathways for modifications of the plan to mitigate adverse (environmental) effects. The development of an EIA has been encouraged or required by various international instruments.276

While the UN Watercourses Convention does not directly require the planning state to carry out an EIA, it nevertheless suggests that if a state which might be affected by the planned measure asks the planning state to provide an EIA, the latter would have to comply with this request if the former bears the costs.277 Additionally, it could be maintained that the assessment and evaluation of possible environmental impacts of a new project on a transboundary watercourse is an inherent prerequisite for complying with the customary obligation not to cause significant transboundary harm278 (see Article 7).

The International Court of Justice (ICJ) supported this view in its judgement of the Pulp Mills Case by linking the interstate notification of planned measures to the satisfaction of the due diligence obligation to prevent significant transboundary harm. It established that conducting an EIA ‘may now be considered a requirement under general international law’ with regard to activities which ‘may have a significant adverse impact in a transboundary context.279’ The importance here is the argument of the court that the duty to notify, linked with the duty to conduct an EIA, exists in customary international law. Hence, it applies to all states – irrespective of the existence of such obligations in the relevant transboundary water agreements.280 However, due to the fact that this obligation is rather open and imprecise, it leaves considerable room for debate as to which elements to include in an EIA.281 An example of an international agreement which provides further information can be seen in the 1991 UNECE Convention on Environmental Impact Assessment in a Transboundary Context.282

275 DA Wirth, ‘Hazardous Substances and Activities’ in Bodansky D, Brunnée J and Hey E (eds), The Oxford Handbook of International Environmental Law (Oxford University Press 2007) at 420.

276 See, for example, 1991 UNECE Convention on Environmental Impact Assessment in a Transboundary Context (Espoo Convention); Article 8 of the 1997 IAEA Joint Convention on the Safety of Spent Fuel Management and on the Safety of Radioactive Waste Management available at <> accessed 30 April 2012.

277 FX Perrez, Cooperative Sovereignty : From Independence to Interdependence in the Structure of International Environmental Law (Kluwer Law International 2000) at 308.

278 See O McIntyre, ‘The World Court’s Ongoing Contribution to International Water Law: The Pulp Mills Case between Argentina and Uruguay’ (2011) 4 Water Alternatives 124.

279 Pulp Mills Case Judgement, para 204.

280 McIntyre, ‘The World Court’s Ongoing Contribution to International Water Law: The Pulp Mills Case between Argentina and Uruguay’ at 124.

281 Perrez, Cooperative Sovereignty : From Independence to Interdependence in the Structure of International Environmental Law at 309.

282 Convention on Environmental Impact Assessment in a Transboundary Context (Espoo Convention, adopted 25 February 1991, entered into force 10 September 1997).

Video: Alistair Rieu-Clarke Video: Alistair Rieu-Clarke Are states required to carry out Transboundary Environmental Impact Assessments (EIAs) under the UNWC?

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