World’s Dams Losing Substantial Storage Because of Silting

Many of the world’s hydroelectric reservoirs are filling with sediment and suffering significant reductions in storage capacity, says the head of a U.N. agency.

BONN, Germany, DE, 2001-12-19 [] “The issue of dams can arouse strong passions on both sides,” says Klaus Toepfer, executive director of the United Nations Environment Programme. “Some people are very much in favour of building dams and others are vehemently against.” “However what we are talking about here is the state and fate of the existing stock of dams and reservoirs on whose waters billions of people depend for not only irrigation and drinking water, but also for industry and production of hydroelectricity,” he told the International Conference on Freshwater in Bonn. On average, 1 percent of water-storing capacity of the globe’s reservoirs is lost annually because of a build up of mud and silt. The current global storage capacity of reservoirs is estimated at 7,000 cubic kilometers. Unless urgent action is taken, one fifth or 1,500 cubic kilometers, will gradually be lost over coming decades, say officials. The loss could be higher and faster if scientific forecasts on climate change prove correct and the rates of deforestation in the developing world are not checked. The levels of erosion from hillsides planted with crops, are 150 times higher than from the same land covered with trees, studies show. “We must act to reduce the loss of forests and to re-afforest cleared areas as part of a comprehensive strategy of watershed management of the world’s river systems,” says Toepfer. “We must also act to reduce the threat of global warming. However, there will always be natural levels of erosion that will contribute to a loss of water storage capability, so I call on engineers to provide technical solutions that offer environmentally friendly ways of extending the lives of the world’s reservoirs.” Sustainable management of reservoirs would take a central role in UNEP’s new Dams & Development Project, based in South Africa. The unit was formed in the wake of the World Commission on Dams, which published its final report last year. The unit has secured funding and pledges of US$2.5 million from the governments of Germany, the Netherlands, Sweden, Switzerland and the United Kingdom. A report, ‘Evacuation of Sediments from Reservoirs’ by Rodney White, highlights techniques that can restore storage capacity of reservoirs, including the method called flushing in which flood waters from heavy rains or mountain melt are used to sweep debris, mud and silt out of the reservoir downstream. White concludes that the technique is likely to work in parts of Central America; areas in North and South America where the rivers are fed by the Rockies and Andes; and parts of Central Africa from Cote D’Ivoire in the west to Sudan in the east; as well as areas in Central Asia where rivers are fed by the Himalayas including Pakistan, India and Nepal and parts of Asia including Cambodia, Vietnam and Thailand. The issue of dwindling capacity of reservoirs is one piece in the puzzle of delivering sufficient quantities of clean water to the world’s people, explains Toepfer. Research shows that large amounts of water used in irrigation is being lost and squandered, with 60 percent wasted in developing countries. Even municipal water distribution systems in developing countries lose 50 percent of water as a result of leaks and poor management, he says.
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