Introduction

What are the issues?

Presently, hydropower is the most widely used form of renewable energy, accounting for 17% of global electricity generation, expected to increase by approximately 3% each year for the next 25 years. Over the last two decades the global hydropower generation has increased by 50%. This includes all types and sizes of hydropower, micro-hydro as well as large dams*. Although energy generation can be the only objective, a reservoir dam can have other purposes as well such as provision of water for drinking and irrigation or water management to avoid flooding.

Potential impacts

• Impacts of reservoirs on terrestrial ecosystems and biodiversity, leading to potentially irreversible loss of species populations and ecosystems;
• Emission of greenhouse gases associated with reservoirs (strongest in tropical areas);
• Impacts of altered downstream flows on aquatic ecosystems, on the natural flood cycle of downstream floodplains and on the salt/freshwater balance in estuaries;
• Upsetting of sediment balance of rivers and coastal ecosystems leading to coastal erosion;
• Barrier effect of dams on migratory species and fisheries in the upstream, reservoir and downstream areas;
• Cumulative impacts of a series of dams on a river system;

• Delay between the start of planning and (uncertain) construction, leading to reluctance to invest in potentially flooded (dam-designated) areas;
• Temporary influx of construction workers during construction; related social tensions;
• Displacement of people and livelihoods: the larger the number of displaced people, the less likely it is that livelihoods can be restored; disruption of downstream livelihoods through changes in provision of ecosystem services;
• Disproportionate levels of displacement and negative impacts on livelihood, culture and spiritual existence of indigenous peoples and vulnerable ethnic minorities;
• Numerous vector-borne diseases, associated with reservoir development in tropical areas, such as malaria, schistosomiasis, Rift Valley fever, Japanese encephalitis;
• Loss of cultural heritage;
• Unequal distribution of the gains and losses of a project across different societal groups and sometimes across borders.

Role of ESIA and SEA

Negative impacts can (partly) be avoided, mitigated and compensated, and positive impacts can be enhanced, by making use of ESIA for individual projects. One example of the level of individual projects is the use of fish ladders that can partly mitigate the negative effects of migration by some fish species. However, most impacts are the result of the location of a hydropower project, for example tributaries located in a national park are more sensitive to the effects of a hydropower project, than tributaries outside such a park. And the cumulative impacts of a number of these projects in a river basin can be considerable. Cumulative and negative impacts can (partly) be avoided or mitigated by applying SEA to support strategic planning of hydropower projects. 

Read more information in NCEA's views on ESIA and SEA for Sustainable Hydropower Development

* International Energy Agency/IEA, 2017