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The damming of the Mekong: major blow to an epic river

By Fred Pearce - posted Friday, 3 July 2009

The Mekong has long flowed freely, supporting one of the world’s great inland fisheries. But China is now building a series of dams on the 4,500km river that will restrict its natural flow and threaten the sustenance of tens of millions of South-East Asians.

The Swift Boats are long gone. The Mekong delta is peaceful now. Vinh Long, where Americans fought skirmishes with the Vietcong, is now a holiday resort. The Westerners heading off into the remoter regions of the enormous delta point nothing more threatening than a camera - and the only ambush they face is at the hands of traders at the nearby Can Tho floating market.

Vietnam is now a fast-growing, Westernising economy. But, paradoxically, peace and prosperity is currently the biggest threat to what is one of the world’s last great wild rivers. Almost half a century of wars in South-East Asia kept engineers away from the Mekong. Their plans for giant hydroelectric dams on the river gathered dust. But all that is changing. And on the delta, they have reason to fear the consequences, for the tens of millions of people who rely on the river’s wildness for their supper could soon see their main source of protein dry up.


Last October, Chinese engineers finished construction of the Xiaowan dam on the upper reaches of the River Mekong, in the remote southern province of Yunnan. The 292m Xiaowan dam is the world’s tallest, as high as the Eiffel Tower. Starting this summer, the hydroelectric dam will for the first time catch the great Mekong flood that rushes out of the Himalayan mountains, and then gathers monsoon rains and snowmelt as it surges through the steep gorges of Yunnan. The reservoir will eventually be 169km long. The first electricity will be generated next year and help keep the lights on as far away as Shanghai, more than 1,930km to the east.

As China rushes to industrialise, a total of eight hydroelectric dams are planned on the Mekong. By 2014, engineers will have completed the Nuozhadu dam, which will be less high but will have an even larger reservoir. The Mekong is destined to become China’s new water tower and electrical powerhouse.

This cascade of dams will be able to store half the entire flow of the Mekong as it leaves China and rushes downstream toward Burma, Thailand, Laos, Cambodia, and Vietnam. In the future, the annual flood will be released gradually as turbines are switched on and off to supply year-round electricity. From then on, the river will rise and fall at the whim of engineers rather than nature.

In late May, a report from the United Nations Environment Programme (PDF 4.44MB) warned that these dams are “the single greatest threat” to the future of the river and its fecundity. The new regime will largely eliminate the river’s annual flood pulse, one of the natural wonders of the world, and wreck the ecosystems that depend on it.

Aviva Imhof, campaigns director at the International Rivers Network, said that the dams will cause incalculable damage downstream. “China is acting at the height of irresponsibility,” said Imhof. “Its dams will wreak havoc with the Mekong ecosystem as far downstream as the Tonle Sap. They could sound the death knell for fisheries which provide food for over 60 million people.”

Experts in downstream countries have been reluctant to criticise China’s policies. But Professor Ngo Dinh Tuan from Hanoi Water Resources University told Vietnamese reporters last month, “If China builds dams to serve power production, the first impact would be a remarkable reduction of aquatic resources. It would be very dangerous for people who live in the lower section.”


Until now, the waters of the Mekong have been a natural resource for humans and nature alike - on a par with the Amazon rainforest. The 4,500km river sustains the world’s second-largest inland fishery, a mainstay of the region’s economy for millennia. It makes the Cambodians, who are among the world’s poorest people, among the best fed. It is a direct result of the intensity of the river’s summer flood, and in particular of one feature of the flood - the river that runs backwards.

That river is the Tonle Sap, a tributary of the Mekong in Cambodia that is the beating heart of the Mekong River system. But according to the author of the UN report, Mukand Babel of the Asian Institute of Technology in Bangkok, Thailand, it is among the river system’s most vulnerable elements. China’s dams could still the beating heart.

For seven months of the year, the Tonle Sap flows from a lake in the centre of Cambodia and joins the main river in front of the royal palace in Cambodia’s capital city, Phnom Penh. But each June, that downhill flow halts, and for five months - until November - the river reverses. This happens because the summer floods increase the Mekong’s flow 50-fold. So much water comes coursing down the Mekong that the river’s main channel cannot contain it.

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First published in Yale Environment 360 on June 16, 2009.

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About the Author

Fred Pearce is a freelance author and journalist based in the UK. He is environment consultant for New Scientist magazine and author of the recent books When The Rivers Run Dry and With Speed and Violence. His latest book is Confessions of an Eco-Sinner: Tracking Down the Sources of My Stuff (Beacon Press, 2008). Pearce has also written for Yale e360 on world population trends and green innovation in China.

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