Tuesday, June 10, 2008

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Lake Cahora Basa

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The Zambezi River drains an area of roughly 1.5 million km2 from Angola to Mozambique. In 1974, the Cahora Bassa Dam was completed about 300 km upstream from where the Zambezi River empties into the Indian Ocean. The dam created Lake Cahora Bassa, the second largest human-made lake in southern Africa. Prior to the dam's construction, surrounding natural ecosystems and traditional agriculture were shaped by annual floods.

As the dam neared completion, experts recommended that Lake Cahora Bassa be filled slowly, over a period of at least two years. Furthermore, they recommended that a minimum flow be maintained, with extra releases to simulate natural flooding, and that the filling of the reservoir should not begin until after the 1975 flooding season. These recommendations were not followed.

The 1972 image (above top) shows a 250-km stretch of the Zambezi River prior to the construction of the Cahora Bassa Dam. The same stretch was flooded, in a single year, following the dam's completion in 1974. In the ensuing years, flooding of the lower Zambezi has been notoriously mistimed. These erratic water releases have negatively impacted hundreds of thousands of downstream residents and decimated the ecosystem of the Zambezi River delta. The 2006 image (above bottom) shows the current extent of the reservoir. Strategies to better manage Cahora Bassa Dam are being explored in order to restore damaged ecosystems and some traditional land use.
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