A huge dam construction project is under way in China in the Three Gorges area on the upper Yangtze River. Apart from the expected benefits of the project, it will nevertheless cause problems, such as flooding upstream, possibly an earthquake, displacing people, eliminating tourist trade to the area, and destroying important archaeological artifacts.
After completion Three Gorges will become world’s largest dam, sinking 13 cities, 140 towns, and 1,352 villages and requiring the resettlement of 2 million people. The dam will also bury hundreds of archeological sites, put several highly endangered species in jeopardy, and infinitely deface the magnificent beauty of the Three Gorges Region. This is the classic example of the devastation that all large dams cause.
In the same category, at Bakun, in Sarawak, Malaysia, the mega dam threatens 70,000 hectares of prime rainforest, and is hugely controversial. Large dams are built in Laos, Lesotho, Argentina, and Chile with the aid of military to suppress opposition.
Despite what promoters say, the academic literature belies that dams and reservoirs are purely benign, they have serious effects including earthquakes, coastal fisheries impacts, mercury pollution of food chains, destruction of local subsistence economies, loss of valuable fisheries and local extinctions, to mention but a few.
Large dams often destroy important, irreplaceable archeological evidence - burial grounds, antiquities, ancient building sites, and more. Although the promoters talk about engineering triumph they have enormous negative side effects that adversaries do not consider as progress, like the forced relocation of millions of people.
In the present planning process, the cost of environmental and social impacts is considered only to the extent required for fulfilling the legal requirements. This does not fully account for the real costs.
Such dams are also short of poverty reduction benefits of decentralized renewables. They are capital-intensive and dependent on large centers of demand and long transmission lines. They are among the most expensive infrastructure projects on the planet. The advocates of large dams regularly underestimate costs and exaggerate benefits. They have regularly underestimated the economic costs of large hydropower projects as well as the number of people requiring resettlement or compensation for lost lands, homes, and sources of livelihood. While costs are on average far higher than predicted, large hydropower dams often generate less power than promised.
The developers of large dams do not take into account the hydrological impacts of climate change. They build dams with designs that do not allow for the new extremes of drought or floods that global warming is predicted to cause. This has serious implications for dam performance – particularly droughts will sharply reduce hydropower generation – and safety.
There is no technology transfer benefit from large dams. Global renewable funds and carbon trading mechanisms are supposed to facilitate the transfer of new technologies from Northern to Southern countries and to provide the support needed to increase production and bring down unit costs of these technologies. These arguments do not apply to large dams, which is already a mature technology and well established in Southern countries.
Large hydro projects have major social and ecological impacts. According to the World Commission on Dams, large dams are responsible for the evictions of 40-80 million people, with many of the displaced receiving no or inadequate compensation. Millions of people have also lost their land and livelihoods, and have suffered because of downstream and other indirect impacts of large dams.
Efforts to mitigate the impacts of large dams typically fail. Many impacts of large dams go unacknowledged or underestimated, and measures to prevent or reduce them frequently fail. Even when people are recognized as eligible for resettlement they rarely have their livelihoods restored.
Large reservoirs can emit significant amounts of greenhouse gases. Rotting organic matter in hydropower reservoirs causes emissions of methane and carbon dioxide. While there is still much scientific controversy over how to measure hydropower emissions and compare them with emissions from fossil fuel plants, it appears that hydro projects with large reservoirs in the tropics can have a greater climatic impact per unit of power generated than fossil fuel generation.
They are slow, lumpy, inflexible and getting more expensive. Because of their huge size and site-specific requirements, large dams take longer to build and are more expensive than other types of power plants. While large dams take on average around six years to build, wind turbines and solar panels can start delivering benefits and repaying loans within months of entering construction. The World Bank has found that the costs of hydropower capacity are steadily increasing because the best sites for dams have already been exploited.
Large dams add capacity to power grids in large lumps, while power demand usually grows gradually. Lumpy capacity additions can mean power shortages before the new capacity comes on-line, then costly over-capacity once the new plant is available.
Large reservoirs are often rendered non-renewable by sedimentation. They are depleted over time by sedimentation, a problem that eventually seriously impedes or ends the ability of a hydro plant to produce electricity. The great majority of annual sediment loads is carried during flood periods. The higher intensity and frequency of floods due to global warming are therefore likely to increase sedimentation rates and thus further shorten the useful lives of reservoirs.
Despite overwhelming evidence, dam proponents are repeating the deadly mistake of the Soviet government - ignoring years of respected research. Asian dams continue to proliferate. And foreign dam builders are right in there looking for short-term jobs at the long-term expense of poor Asians.
The projects implemented without public participation and consent are likely to face high risk of delay and cost over-run apart from creating serious social tensions.
The day of the large dams might be over, but we have no shortage of challenges. We all need to become better water managers, and one of the important ways we do that is to change the perspective with which we approach present and future challenges.
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