Where have all the wild rivers gone

Quote: Where have all the wild rivers gone? 23 April 2005 From New Scientist . Fred Pearce Taming the flowTHE untamed rivers of the world are rapidly becoming extinct. Most big river systems, including the 20 largest and the eight most biologically diverse, now have dams on them - and it could be only a matter of time before the last untamed flows are tapped for hydroelectricity or irrigation. The first systematic study of almost 300 of the planet's largest river systems finds that most of the remaining wild rivers are in the empty Arctic tundra and northern boreal forests. The largest surviving wild river system is the Yukon in remote northern Canada, the world's 22nd largest river by volume. Europe's last three undammed river systems are all in northern Russia, the Onega, Mezen and Pechora. But 82 per cent of the river systems in deserts and 99 per cent around the Mediterranean are dammed. What is more, the eight rivers that run through the largest variety of ecosystems - the Amazon, Orinoco, Ganges, Brahmaputra, Zambezi, Amur, Yenisei and Indus - are all extensively dammed. Christer Nilsson, a landscape ecologist at the Umeå University in Sweden and head of the research team, says many arid parts of the world have no untamed river systems (Science, vol 308, p 405). Regulating the flow may be especially harmful to ecosystems in these dry regions, where species often depend on river water. Nilsson is calling for "an international attempt to save some of the last wild rivers". But pressure to tame these rivers continues. The Salween, which runs for 2400 kilometres from China through Burma and Thailand, is about to be dammed for the first time. Thirteen dams are planned for this river, including the giant Tasang dam on the stretch flowing through Burma. Other threatened virgin river systems include the Rajang in Malaysian Borneo, the Jequitinhonha in Brazil, the Cá in Vietnam and the Agusan on the island of Mindanao in the Philippines. The damming of great rivers is "among the most dramatic, deliberate impacts that humans have had on the natural environment," says Nilsson. Thousands of dams across the planet hold back more than 6500 cubic kilometres of water in reservoirs. Many rivers have "staircases" of dams that can hold more than their whole annual flow - or even four years' worth, in the case of the Volta in west Africa. Such total control could risk triggering future water wars in some parts of the world. Turkey has enough reservoir space on the headwaters of the Tigris and Euphrates river system to shut down the entire flow of both rivers into Iraq and the Gulf for more than a year. From issue 2496 of New Scientist magazine, 23 April 2005, page 10