Dams have probably existed for about as long as humans have had agriculture, to control water flow and to use the hydraulic energy for a water mill. Since the 19th century, dams have also been used to convert the hydraulic energy into electricity. There are several methods, but they all rely on the dam (in jargon called a hydroelectric power station) converting the energy of flowing water into electricity through a turbine and generator.
There are all sizes of hydroelectric power stations, varying from ‘pico hydro’, which is usually just a few pipes diverting water from a river instead of a dam, to large and specialized industrial facilities. The large dams generate a lot of energy but have also drawn a lot of criticism because they involve large-scale landscape restructuring. This casefile takes a closer look into that debate, and ignores issues that might come into play around the smaller scale hydroelectric power stations.
The largest hydroelectric power stations in operation as of 2011 are the Three Gorges Dam in China, Itaipu, shared by Brazil and Paraguay, Huri in Venezuela, Tcuruí in Brazil and the Grand Coulee in the United States. Power from hydroelectric power stations in 2008 was about 15% of total power production and is by far the largest renewable energy source in use, providing between 80% - 85% of total renewable energy production.
Hydroelectric dams burn no fossil fuels so emit no greenhouse gasses at all in producing energy. Suppose we replace all coal fired power stations with hydroelectric power stations. In 2010, over 42% of global electricity production was produced through coal, accounting for over 28% of global carbon dioxide emissions. Since there is more than enough potential capacity for hydropower, we could hypothetically completely replace coal and even other fossil fuels for electricity, thus helping cut down greenhouse gas emissions massively.
Hydroelectric dams don’t reduce carbon dioxide emissions. Dams currently hold off about 15% of global freshwater runoff. If we want to sustain biodiversity and river-related goods and services, we can’t easily increase the number of dams. Also: building dams requires cutting down forests, which themselves are important tools in combating greenhouse gases, since they consume and ‘lock up’ carbon dioxide. Plus, the construction of the dams themselves releases carbon dioxide. Finally: global energy demand is expected to continue increasing, meaning that hydropower will probably just be added to the supply and not replace coal.
In 2010, about 1.4 billion people had no access to electricity. Hydropower provides a source of energy that is cheaper even than conventional coal. Large dams can last for over a hundred years and are easy to switch on and off according to demand, making them very cost-effective. Given that having no access to electricity makes work and study nearly impossible, alleviating global poverty by giving access to electricity is an important step to take.
Hydroelectric dams require massive initial investments. True, dams generate cheap electricity, when the dams are eventually built. But building dams is incredibly costly. Actual costs for hydropower dams are almost always far higher than estimated; in a number of cases, the actual cost was more than double the estimated cost. The Itaipu Dam in South America cost $20 billion and took 18 years to build. This was 488% higher than originally estimated. Given that there are cheaper alternatives than large-scale dams for renewable and accessible energy, dams aren’t worth it from an economic perspective.
The large water reservoirs created by hydroelectric dams can provide facilities for water sports and can become tourist attractions themselves. The reservoirs can be used for irrigation to help farmers and can be a means for flood control. A prime example of this is the Tennessee Valley Authority, an organisation responsible for flood control, electricity generation, economic development and even fertilizer generation in the Tennessee Valley in the U.S., spanning parts of Alabama, Mississippi, Kentucky, Georgia, North Carolina and Virginia.
As well as benefits hydroelectric dams have added dangers. Dams increase the risk of earthquakes, because the weight of the water-reservoir impacts the Earth’s crust underneath. Moreover, big dams run the risk of bursting, causing massive damage in their wake. The bursting of the Chinese Banqiao dam in 1975 is estimated to have cost about 230,000 lives.
Hydroelectric dams emit a lot of methane, which is an even more potent greenhouse gas then carbon dioxide. This happens when the plants and vegetation submerged in the reservoir start to rot under water: they then produce methane which bubbles up and is released into the atmosphere. On balance, some dams produce more greenhouse gasses than conventional power plants running on fossil fuel.
Hydroelectric dams can mitigate methane emissions. Dams can capture the methane released from their reservoir and even use it to their benefit: an experimental project in Brazil showed that hydroelectric dams can capture the methane and burn it to produce even more energy, whilst at the same time preventing the methane from being released.
Large dams wreak havoc with the environment: they destroy habitats and ecosystems both further upstream and downstream. They prevent salmon from swimming upstream to spawn. The water going through them is often warmer and devoid of nutrients, depriving downstream riverine wildlife of their natural habitat. A shocking example is China’s Three Gorges Dam, which Scientific American called ‘an environmental disaster’.
Hydroelectric dams can mitigate the ecological impact. Hydroelectric dams can take steps to mitigate their environmental impact. For example, for salmon, dams these days have ‘fish ladders’, allowing them to reach their spawning grounds. For these and other sustainability measures, the International Hydropower Association developed several guidelines and protocols to minimize ecological impact as far as possible.
What applies to the environment, also applies to the human communities. Building dams often involves relocating people and removing them from their ancestral homelands. For example, China’s Three Gorges Dam involved relocating 1.3 million people, involved severe human rights abuses and has had dire social consequences.
Hydroelectric dams don’t destroy communities, governments do. Building dams only violates human rights if the governments building them do so. That’s why we never heard of large-scale human rights violations when the Hoover Dam in the United States was built. Moreover, responsible dam builders in the International Hydropower Association have taken steps to ensure they build dams with the utmost respect for human rights, through the guidelines mentioned above.
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