A systematic process for evaluating the potential environmental effects of a proposed project or development before it proceeds. EIAs are legally required in most countries and are essential for protecting water resources from development impacts.
Environmental Impact Assessment (EIA) is a formal, systematic process used to identify, predict, evaluate, and mitigate the environmental effects of proposed projects, plans, or policies before a decision is made on whether to proceed. Established by the U.S. National Environmental Policy Act (NEPA) in 1969 and since adopted by over 190 countries, EIA is one of the most widely practiced environmental management tools worldwide. For water resources, EIAs evaluate potential impacts including changes to surface water flow patterns and quality, groundwater levels and contamination risk, wetland loss, aquatic habitat alteration, sediment transport disruption, and downstream effects on water users and ecosystems. The EIA process typically includes screening, scoping, baseline studies, impact prediction, significance evaluation, mitigation measures, public participation, and post-project monitoring. Environmental Impact Statements (EIS) for major federal actions in the United States must consider cumulative impacts, indirect effects, and alternatives including the no-action alternative. For dam construction, mining, large-scale irrigation, and industrial development, water-related impacts are often the most significant components of the EIA. Strategic Environmental Assessment (SEA) extends the EIA concept to policies, plans, and programs, addressing cumulative and large-scale water resource impacts at a higher decision-making level.