The research paper called "Dams and Floods" shows that dams are often designed with a very poor knowledge of the potential for extreme flood events. Where data does exist it may fail to consider current risks such as increased rainfall due to climate change or increased run-off of water from land due to deforestation or the drainage of wetlands. The loss of these natural sponges for floodwaters within the river basin increases the risk of extreme floods.
"Dams carve up landscape like a jigsaw puzzle in the name of providing benefits to people," said Biksham Gujja, Head of WWF's Freshwater Programme. "But the pieces often never fit again and fragmented nature can result in greater losses for generations to come."
According to the paper by scientific writer Fred Pearce, lack of adequate information means that dams are often built without adequate spillways to cope with extreme floods. In a 1995 study of 25 Indian dams, World Bank engineers calculated the amount of water that the dams should have been able to release at the height of a flood.
In each case, they found the expected floods were greater than those that the dams had been built to discharge over their spillways - two could only cope with one seventh of the expected peak discharge. Furthermore, dam managers often leave it too late to make emergency releases of water at times of very high rainfall and exceptional river flows. This is because their primary purpose is to generate hydroelectricity and provide water for cities, as well as preventing flooding down stream. However as the reservoir overfills they are forced to make releases of water that are far greater and more sudden than flows that would have occurred during the natural river flooding.
WWF recommends that where dams must be built, the storage and release of water must be in tune with the natural river system and the needs of the people who rely on the river down stream such as fishing communities and floodplain farmers.
"With all that we know now, governments and dam contractors should think twice about starting some of their projects. Our efforts should be spent on technologies that provide water and energy to people without destroying their natural environment. This is also in keeping with findings of the WCD," Biksham Gujja added. (WWF Gland, Switzerland / June 2001)
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