Large Dams Correlated with Poor Water Quality

Large-scale Dams Are Likely Having a Detrimental Impact on Water Quality and Biodiversity Around the World, According to a New Study

Focusing on the 50 most substantial river basins, researchers with International Rivers, a watchdog group, compiled and compared available data from some 6,000 of the world's estimated 50,000 large dams. Eighty percent of the time, they found, the presence of large dams, typically those over 15 metres high, came along with findings of poor water quality, including high levels of mercury and trapped sedimentation.

While the investigators are careful to note that the correlations do not necessarily indicate causal relationships, the say the data suggest a clear, global pattern. They are now calling for an intergovernmental panel of experts tasked with coming up with a systemic method by which to assess and monitor the health of the world's river basins.

The group points to the Tigris-Euphrates basin, today home to 39 dams and one of the systems that has been most "fragmented" as a result. The effect appears to have been a vast decrease in the region's traditional marshes, including the salt-tolerant flora that helped sustain the coastal areas, as well as a drop in soil fertility.

The State of the World project tracks the spread of dam-building alongside data on biodiversity and water-quality metrics in the river basins affected. While the project is using only previously published data, organisers say the effort is the first time that these disparate data sets have been overlaid in order to find broader trends.

Dam-building boom

Today, four of the five most fragmented river systems are in South and East Asia, according to the new data. But four others in the top 10 are in Europe and North America, home to some of the most extensive dam systems, especially the United States.

For all the debate in development circles in recent years about dam-building in developing countries, the new data suggests that two of the world's poorest continents, Africa and South America, remain relatively less affected by large-scale damming than other parts of the world.

Of course, both Africa and South America have enormous hydropower potential and increasingly problematic power crunches, and many of the countries in these continents are moving quickly to capitalise on their river energy.

According to estimates from International Rivers, Brazil alone is currently planning to build more than 650 dams of all sizes. The country is also home to some of the highest numbers of species that would be threatened by such moves.

Economic burden

Particularly for increasingly energy-starved developing countries, concerns around large-scale dam-building go beyond environmental or even social considerations.

Energy access remains a central consideration in any set of development metrics, and lack of energy is an inherent drag on issues as disparate as education and industry. Further, concerns around climate change have re-energised what had been flagging interest in large dam projects, epitomised by last year's decision by the World Bank to refocus on such projects.

Yet there remains fervent debate around whether this is the best way to go, particularly for developing countries. Large dams typically cost several billion dollars and require extensive planning to complete, and in the past these plans have been blamed for overwhelming fragile economies.

A new touchstone in this debate came out earlier this year, in a widely citedstudyfrom researchers at Oxford University. Looking at nearly 250 large dams dating back as far as the 1920s, they found pervasive cost and time overruns.

Source: IPSNews

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