Environmental impact assessment (C2.05)


Environmental Impact Assessment (EIA) is a tool for anticipating the environmental impacts of policy changes and new developments, enabling the incorporation of management, mitigation or control measures into project and policy design. It is routinely used all around the world to improve the planning of projects and is increasingly conducted to examine strategies, policies, plans, and sector programmes. In those cases, it is known as Strategic Environmental Impact Assessment (SEIA) or Strategic Environmental Assessment (SEA). EIA is required when projects are likely to have significant effects on the environment and are typically the responsibility of Impact Assessment Committees (B1.04). Increasingly EIA’s are a legal requirement before planning permission is granted to proceed with a planned development. A drawback is that EIA’s are primarily project specific and do not consider the cumulative aspects of historic or future developments.

Criteria, sometimes prescribed by laws or regulations, for deciding whether water use or water-related projects should be subject to EIA include:

  • The size or scale of the project (e.g. described by design capacities);
  • The sensitivity of the affected area (e.g. wetlands, wildlife habitats and biodiversity);
  • The character or complexity of the likely impacts (e.g. physical impacts from hazardous wastes or social impacts (for instance in resettlement schemes).

The basic methodology of EIA is to study the environment in which a project is planned (the “baseline”), describe the activities that will take place during each phase of a project (i.e. the construction, operation and decommissioning), describe the likely environmental impacts and, where significant adverse impacts are predicted, and develop an Environmental Management Plan (EMP) to mitigate them. A programme to monitor changes from project impacts in environmental parameters forms part of the EMP.

Impacts of particular importance in many projects are:

  • Projected quantitative changes in availability of water for beneficial uses, such as fisheries, recreation and tourism, potable water supply, irrigation, industrial use and aesthetics;
  • The extent to which receiving water quality standards and/or other beneficial use objectives will be achieved;
  • The size of the water body that will be positively or negatively affected by any discharges, and the magnitude of the changes in water quality parameters;
  • Public health impacts from chemical and/or bacteriological pollution;
  • Socio-economic impacts (see C2.03; C2.06).

Lessons learned

  • The best results are often reached when EIAs of progressive level of detail are mainstreamed in the planning, design and implementation process, which permits an early consideration of alternative schemes and an adjustment of project designs at times when most flexibility exists. Once the design and siting of a development are complete, any further mitigation of environmental effects will rely on “end-of-pipe” adjustments or compensation provisions, and these are usually the costliest and the least effective environmental management options.
  • EIA facilitates public consultation by providing a context in which the public can both learn about and express opinions on development proposals and their envisaged effects. People potentially affected by the project can exert influence to reduce adverse impacts, maximise ancillary benefits, and ensure that they receive appropriate compensation.
  • EIA allows the consent granting authority to make better decisions, such that environmental (and social) costs and benefits are considered alongside the technical and financial costs and benefits. Conditions that ensure the most efficient use of resources can appropriately be incorporated into the EMP.