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Damming the world's mightiest rivers

Brazil's Belo Monte dam complex will rank third in the world for installed capacity, but may also set a record for biodiversity loss Brazil's Belo Monte dam complex will rank third in the world for installed capacity, but may also set a record for biodiversity loss Usina Hidrelétrica Belo Monte
15 Mar
An ‘unprecedented boom’ in dam construction on three of the world’s largest rivers could have dire environmental consequences

They dominate the hydrological systems of three major continents, and collectively hold one-third of the world’s freshwater fish species, many of which are endemic to their respective river basins. Yet, the Amazon, Mekong and Congo rivers have become ever more attractive to developers keen to increase the capacity for relatively low carbon hydropower energy. Until now, dam construction on all three rivers has been relatively small-scale, located only in upland tributaries. However, a new report by 40 international scientists draws attention to nearly 450 new dams proposed for these three major rivers, with many others already being built. The report warns of the negative environmental and economic consequences that could arise without sufficient analysis of the outcomes.

‘Major dams are usually built where rapids and waterfalls boost the hydropower potential, the same sites where many unique fish species adapted to life in fast water are found,’ explains Dr. Kirk Winemiller from the Department of Wildlife and Fisheries Sciences at Texas A&M University. ‘We wrote the paper to bring global attention to this problem, partly in hopes of stimulating research on tropical rivers, and partly to stimulate better approaches for hydropower development that balance true costs and benefits in the context of cumulative impacts.’

Far too often, major hydropower projects are approved and begun before any serious assessments of environmental and socioeconomic impacts have been conducted

One key impact is the effect this vast succession of dams will have on fish migrations. There are 2,300 known species of fish in the Amazon, around 1,000 in the Congo and 850 in the Mekong, and the report argues that insufficient attention has been paid towards how their various migrations will be affected, and what impact this will have on the human populations dependent on these stocks for their survival. There are also major concerns regarding how the 334 dams currently planned for the Amazon, for example, might further deteriorate a rainforest already battling against deforestation.

‘Transparency of the ramifications caused by these structures is limited,’ says Winemiller. ‘For example, Brazil’s Belo Monte complex, that is nearing completion on the Xingu River, will rank third in the world with installed capacity of 11,233MW. However, it may also set a record for biodiversity loss owing to its location.’

He also highlights the Tonle Sap in Cambodia, host to one of the world’s most important inland fisheries, with species that migrate there from the Mekong. The inland fisheries in the Lower Mekong were recently valued at $17billion a year, and directly support three million people in Laos, Thailand, Cambodia and Vietnam.

‘Far too often in developing countries, major hydropower projects are approved and begun before any serious assessments of environmental and socioeconomic impacts have been conducted,’ says Winemiller. The report calls for dam sites to be evaluated not only for economic potential, but also for environmental sustainability, in order to prevent construction of the very worst offenders.

This was published in the March 2016 edition of Geographical magazine.

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