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The start-up of one of Southeast Asia's biggest hydropower dams has launched a new round of debate over how much damage the megaproject might inflict on the environment.
Backers led by the World Bank and the Asian Development Bank (ADB) say that the $1.5 billion Nam Theun 2 (NT2) dam in central Laos has already taken its most severe toll on the environment: Filling the reservoir in 2008 involved resettling 6200 people and inundating 450 square kilometers of the Nakai Plateau. But critics say that the ecological harm has only just begun. "NT2 will lead to very serious impacts" for more than 100,000 people living downstream, says a U.S. expert on water issues in Laos who asked to remain anonymous out of fear of offending the Lao government. "World Bank and ADB will, I expect, regret ever getting involved in this project." Not so, says a World Bank official. "A thorough analysis of probable downstream impacts, as well as a credible and comprehensive mitigation and compensation program, was critical to getting the World Bank to support NT2," he says. Both sides agree that a major experiment in hydrology and ecology is now under way.
The project, run by the Nam Theun 2 Power Company (NTPC), diverts water from the Nam Theun River, a tributary of the Mekong River, into Nakai Reservoir, from which water is released via a 27-kilometer channel to another Mekong tributary, the Xe Bang Fai. The Lao government will plow its $2 billion share of revenue from electricity sales in the next 2 decades into a national fund for alleviating poverty. Other aspects of NT2 have gotten a thumbs-up from some experts, who stress the good it will do for the impoverished Nakai Plateau. The resettlement plan is "state of the art," says Thayer Scudder, an anthropologist at the California Institute of Technology in Pasadena who, with two colleagues, has served as an NT2 expert panel since 1997. Still, Scudder cautions, "implementation is the name of the game, not planning."
Tensions over NT2's environmental legacy have simmered for years. "Diverting a large amount of water from one river basin to another, via a large reservoir with deoxygenated and eutrophic water in it, will greatly change the hydrology and water quality of the Xe Bang Fai," says the U.S. expert, who predicts that erosion will also be a major problem. Mitigation measures, he insists, are insufficient.
When the dam began generating electricity and water flow changed last month, critics pounced. In a 26 March letter to the World Bank and ADB, the advocacy groups International Rivers and Mekong Watch asserted that water quality on the upper Xe Bang Fai deteriorated when river levels rose 3.6 meters. The groups claimed that the rapid rise had washed away gardens on the river's banks and that fish had "disappeared from the river." They also charged that NTPC has failed to provide adequate alternative drinking water supplies. "The project is violating people's human rights by preventing access to clean water and by destroying critical food sources without providing compensation," contends Ikuko Matsumoto, Lao program director for International Rivers. The letter called on the World Bank and ADB to suspend dam operation and strengthen downstream mitigation measures.
Such criticism is unwarranted, NT2 backers say. In an 8 April letter to International Rivers and Mekong Watch, the World Bank and ADB asserted that "considerable progress" has been made with the downstream mitigation and compensation program and that "effective erosion, water quality, fish catch, and socioeconomic monitoring systems" are in place. The letter notes that some 500 boreholes and pumps have been installed to provide drinking water, for example. Thanks in part to structures such as an aeration weir, "initial results show that water quality in the Xe Bang Fai is not significantly different to how it was prior to the project," says NTPC spokesperson Aiden Glendinning. "These results were shared with before they made their claims of pollution and fish loss, for which no evidence has been found anywhere along the river," he says.
Work on NT2 has yielded one welcome surprise: a find of 38 large-antlered muntjacs, a rare deer, on the Nakai Plateau (Science, 4 September 2009, p. 1192). But with the electrical spigot now open, the question is whether NT2 will improve or worsen the welfare of communities downstream. On that count, the verdict on NT2 is not yet in.