HydroElectric Energy: Like Ice in a Fire… Something for nothing you'll never acquire.

Mark Brown, with this story, wants to flag for the reader the need for adoption a more holistic perspective when discussing hydroelectricity. We have all learned that hydroelectric energy has several positive aspects for sustainability. That is, it is a clean, efficient and reliable form of energy with negligible GHG emissions, and an effective technology for flood protection and stabilization of water supply (both for drinking water and irrigation). However, it is important to consider that there is also another side to this coin that needs to be considered. It is becoming more and more evident that the continuous expansion of large hydroelectric projects around the world also entails negative effects, which are associated with an increasing disruption of local ecosystems and local socio-economic communities. In the cases of conflicts, it is becoming more and more difficult to define clearly which costs and which benefits should be considered, by whom and weighted how they should be weighted.

Mark Brown

Mark Brown

Dr. Mark T. Brown is professor of Environmental Engineering Sciences and director of the Center for Environmental Policy at the University of Florida.  His intere...

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Electricity generated in hydroelectric dams is considered a renewable, clean, and efficient energy source. It is said to emit very low levels of greenhouse gases when compared to fossil fuels. The operating costs per MW of generating capacity are among the lowest of all types of electrical generating facilities. As a renewable source, hydroelectricity is generally more available on demand than others since water flows often can be controlled.


Hydroelectricity is the most widely used form of the so-called renewable energies. Worldwide, the installed capacity of hydroelectric facilities in 2006 was 777 GWe (USEIA, 2010), which supplied 2997 TWh of hydroelectricity. This was approximately 20% of the world's electricity, and accounted for about 86% of electricity from renewable sources (USEIA, 2010). The largest dam in the world is China’s Three Gorges Dam with an installed capacity of 25.6 GWe. The second largest is Itaipu on the Paraná River on the Brazil-Paraguay border with an installed capacity of 14 GWe.

Of the 25 Hydroelectric projects currently under construction world wide (totaling 107 GWe capacity) …19 are in China. There are approximately 19 dams in the planning stage worldwide with a combined capacity of 166 GWe, of which 8 are in China. Many of the planned dams are mega projects on some of the largest rivers in the world that have yet to be dammed because of their size.

Benefits of Hydroelectric Dams

Generally proponents of hydroelectricity agree on the following benefits of dams:

Dams stop the flooding of rivers and the resulting losses of life and property. About 13% of all large dams in the world – in more than 75 countries – have a flood management function (WCD, 2000).

They are a clean, efficient, and reliable form of energy emitting lower levels of pollutants and GHG emissions that conventional fossil fuel generating facilities. Their overall average efficiency is about 90 percent.

They can supply water for local population for drinking needs. Globally, about 12% of large dams are designated as water supply dams (WCD, 2000).

While their initial cost is high; they are very inexpensive to operate. Their operating costs appear to be about 25% of conventional fossil fuel and nuclear plants if fuel costs are included.

Many dams enhance irrigation in summer seasons and dry months as well as in arid climates. It has been estimated that half the world’s large dams were built exclusively for irrigation, an estimated 30 to 40% of the 268 million hectares of irrigated lands worldwide rely on dams producing an estimated 12-16% of world food production (WCD, 2000).

Many dam reservoirs support large fisheries a new source of revenue and protein for local populations.

Global Dam Construction
By 1949 about 5000 large dams had been constructed worldwide, three-quarters of them in industrialized countries. By the end of the 20th century, there were over 45000 large dams in over 140 countries. The top five dam-building countries account for nearly 80% of all large dams worldwide. China alone has built around 22000 large dams, or close to half the world’s total number (WCD,2000).

Water Supply
The extent to which cities rely on dams and reservoirs for urban and industrial water varies greatly even within countries. In the Saxony region of Germany, reservoirs provide 40% of the water supplied to two million people, while Los Angeles derives 55% of its water supply from local ground water resources and 37% from a system of reservoirs and pipelines that bring water from more distant locations. Ho Chi Minh City in Vietnam gets 89% of its water from surface sources, whereas Hanoi gets 100% from ground water. (WCD, 2000)

Flood Protection
Evidence in the WCD, data base confirms that while dams have provided important flood control benefits, some dams have increased the vulnerability of riverine communities to floods.

Disadvantages of Hydroelectric Dams

Trends in Fisheries
Data from the Tucurui dam in Brazil illustrate the changing nature of fish production in the downstream, reservoir and upstream areas. The harvest upstream of the reservoir remained stable for the first 10 years or more, but now appears to be increasing. Meanwhile, the downstream fishery has shown a continued downward trend. However, the reservoir fishery has expanded tenfold in the last 20 years, with the result that the total fishery (upstream, downstream and in the reservoir) has tripled in size to 4700 tonnes per year since the dam was created.

Most opponents of dams first suggest that not all the suggested benefits are actually true, especially on an individual basis. The following are disadvantages suggested by opponents of dams:

In many new dam sites because of flat terrain the areas flooded are very large causing significant ecosystems disruption.

Dams displace people, resulting in changes in life style and customs. It has been suggested that as many as 472 million people worldwide have been affected by dams (Richter et al. 2010). The World Commission on Dams, a World Bank sponsored initiative backed by both dam supporters and critics, estimated that 40 to 80 million people have been displaced by dams (WCD, 2000).

Dam reservoirs often submerge large amounts of plant biomass, which decays anaerobically producing significant quantities of methane, a greenhouse gas (GHG) that is 25 times more potent than CO2. This is especially important in the tropics and with the very large dam projects. Fearnside (2004) calculated that the Curua-Una dam in the Amazon released 3.5 times the green house gases than would have been released burning fossil fuels to generate the same quantity of electricity.

Dams affect migratory patterns of fish and other animals causing declines in populations and in some cases local extinctions.

Dams trap sediments and nutrients robbing downstream ecosystems and agriculture of these valuable resources and reducing productivity.

Dams lower discharge quantities and pulsing of discharge waters, which causes increased salt-water intrusion into the deltas.

Dam reservoirs in the tropics change flowing waters to still waters that creates more habitat for the snails and mosquitoes that carry malaria, dengue fever and schistosomiasis.

Dams affect water temperatures often increasing temperatures as a result of reservoir storage and when released affect downstream animal life.

Dam operation changes pulsing patter of river flow downstream in some cases causing unusually high discharges at times and unusually low discharges at other time all of which have deleterious impacts on river ecology and geomorphology.

GHG Emissions
A first estimate suggests that the gross emissions from reservoirs may account for between 1% and 28% of the global warming potential of GHG emissions.

Little recognized until recently, but potentially extremely important, are the potential negative consequence of large dams related to transboundry issues between nations. Many rivers flow through several countries and are relied upon for many important inputs to economies… from agriculture, to fisheries, to transportation. Treaties are often not enough to stave off potential long-term conflicts over water and the electricity that is produced since dam projects span many years and policy makers often do not have the foresight to understand the longer-term consequences. A good example is the current rift between Brazil and Paraguay over the sale of excess electricity (Brockner, 2009).


Ecological Impacts
The modified habitats resulting from large dams often create environments that are more conducive to non-native and exotic plant, fish, snail, insect, and animal species

Currently there are over 45,000 large dams in the world generating about 20% of the world’s electricity. Since the environmental and social costs of large dams have been poorly accounted for, their true economic profitability remains elusive (WCD, 2000).

Large dams represent tradeoffs: e.g. trading electricity for the pulse regime of a productive downstream wetland delta and fishery, or protection from flooding for loss of sediments and erosion of downstream floodplains and deltas, or irrigation water for increased incidence in waterborne diseases. Some countries, especially in Africa rely on hydropower as their primary source of energy and the tradeoff between security of energy source (ie non fossil fuel) versus transboundary conflicts are yet to be fully understood or reckoned with.

Comprehensive emergy evaluations of two dam projects conducted by the author (Tucurui, Dam in Brazil, [Odum, and Brown,1986], and a dam on the Mekong in Thailand [Brown and McClanahan, 1996]) found that the ultimate values of these large dam projects to the economies of each country were marginal. In both cases, the value of sediments trapped and thus lost to downstream ecosystems and fisheries were within the same order of magnitude as the electricity generated.The loss of forest productivity in the case of the Tucurui dam yielded a break even ratio of 2100 hectares Ecological Impacts The modified habitats resulting from large dams often create environments that are more conducive to nonnative and exotic plant, fish, snail, insect, and animal species of reservoir area for each MW of generating capacity, thus when combined with other impacts, made the dam project’s overall contribution to the economy questionable.

There is no question that dams have made an important and significant contribution to human development, and the benefits derived from them have been considerable (WCD, 2000). Yet, to secure those benefits, very often an unacceptable amount of damage to social and environmental systems has resulted. The tradeoffs need be elucidated so that future decisions have the benefit of hindsight. Unfortunately, in searching the scientific literature, we learned that there are practically no studies of the environmental, social and economic performance of the 45,000 older dams that currently exist. What is needed is a post facto integrated, synthetic and systematic evaluation of large dams that includes their energetic, ecologic, social and economic costs and benefits. With most the vast majority of smaller rivers already dammed, what remains globally, are ever-larger dam projects translating into ever-larger risks. We strongly urge a go-slow policy, a policy grounded in bio-physical realities to temper economic dreams.

Literature Cited

  1. E. Brockner, The Itaipu Dilemma, Diplomatic Currier: a Global Affairs Magazine, Issue II Vol.I. Spring 2009.
  2. M.T. Brown and T. McClanahan, Emergy Analysis Perspectives for Thailand and Mekong River Dam Proposals, Ecological Modeling 91, 1996, pp105-130.
  3. P.M. Fearnside, Do hydroelectric dams mitigate global warming? the case of Brazil's curuá-una dam, Mitigation and Adaptation Strategies for Global Change, Vol 10, 4, 2005, pp675-691.
  4. Odum, H.T., and M.T. Brown, Energy Systems Overview of the Amazon Basin, Report to the Cousteau Society, Gainesville, FL: Center for Wetlands, Univ. of Florida, 1986, 190 pp. (CFW-86-03).
  5. Richter, B.D., S. Postel, C. Revenga, T. Scudder, B. Lehner, A. Churchill, M. Chow, Lost in development’s shadow: The downstream human consequences of dams Water, Alternatives, 3, 2, 2010, 14-42.
  6. USEIA, United Stated Energy Information Agency, Department of Energy, 2010, Retrieved 06/08/10 from: EIA - International Energy Data and Analysis
  7. WCD, Dams and Development: a new framework the report of the world commission on dams for decision-making, Earthscan Publications Ltd, London and Sterling, VA, 2000, 356p. (Article)

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