Damaged by dams

Posted: 14 July 2003

Increasingly, large dams are damaging aquatic ecosystems and displacing millions of people - all in the name of development with highly dubious benefits.

Worldwide there are now about 45,000 large dams in operation. Built to provide hydropower and irrigation water and to regulate river flow to prevent floods and draughts, they have had a disproportionate impact on the environment. Collectively, they have inundated more than 400,000 square kilometres of mostly productive land - an area the size of California. Fully one-fifth of the world's freshwater fish are now either endangered or extinct. Somewhere between 40 and 80 million people have been displaced by dams, forced to relocate to other, often less productive, land.

Click here for a graphic showing the number of new dams that were under construction in 1998 and also showing river fragmentation and flow.

A study by the World Commission on Dams, published in 2000, found that large dams have a very mixed record.

On one hand:

  • In 140 countries, dams provide cheap hydroelectric power. On a global scale, dams account for 19 per cent of the world's electricity generation and supply, through irrigation, almost 16 per cent of the world's food.
  • Some dams continue to operate after 30-40 years, providing water and electricity.

On the other hand:

  • Large dams have led to the loss of forests and wildlife habitat and the loss of aquatic biodiversity - both upstream and downstream.
  • Large dams have, in most cases, systematically failed to assess and account for the range of potential negative impacts on displaced and resettled communities. With up to 80 million people displaced from their homes and many more living downstream suffering from unintended effects (eg. Loss of fisheries), mitigation efforts have, for the most part, been cosmetic and ineffective.

According to the Commission, large dams may be on their way out:

  • Mini-hydropower plants have proved to be far cheaper to build and more economical to run than originally forecast; plus they have minimal impacts on the environment.
  • Better management to reduce the demand for water has great potential to reduce water stress and hydropower requirements.
  • Improved systems management, particularly for irrigated agriculture, has tremendous potential for reducing waste, while increasing the efficiency of irrigation systems.

More facts

New research from the University of Umea in Sweden and the Nature Conservancy in the United States, published in April 2005, found that more than half of the world's large rivers are fragmented and regulated by dams, including all the largest and the most biologically diverse rivers.

The study shows that flow in 172 of the 292 largest rivers is regulated by dams, and that this number would be larger if irrigation were included. There are dams in the world's 21 largest rivers and in the eight rivers that are biologically and geographically most diverse.

More than 45,000 dams over 15 metres (49 feet) high have been constructed and together they can store more than 6,500 cubic kilometers of water - equal to 15 per cent of the annual freshwater runoff in the world.

Link: World Commission on Dams: Large Dams Cross-Check Survey. A publication that may be of interest is double issue 3-4/99 (150 pages) of the journal of Indigenous Affairs on Dams: Indigenous peoples and ethnic minorities", published by the International Working Group for Indigenous Affairs based in Copenhagen. It contains seven case studies from Asia, Europe and Latin America. To visit the IWGIA website, click here.