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The Forgotten Downstream Victims of Large Dams

Not only do large dams disrupt some of the world's most productive ecosystems but they've also negatively impacted 472 million people.

An estimated 472 million people have likely been negatively impacted by the downstream impacts of large dams. This is the main finding of a scientific study which was just published by a group of eminent global freshwater experts. The study documents the impacts which dams have had on some of the world's most productive ecosystems, and recommend measures which can prevent the further loss of floodplains that sustain unique ecosystems and millions of people.

A Port Underwater

In the 1970s, Kharochan was a bustling town in Pakistan's Indus Delta. The local farmers grew rice, peas, coconuts, mango and guava on their rich soils. From the nearby harbor Sokhi Bandar – the "Port of the Prosperous" – traders exported silk, rice and wood. When I visited in 2006, no traces of prosperity were left in Kharochan. The port had been swallowed by the sea, and the groundwater had become saline in large parts of the delta. A white crust of salt covered the earth, and turned Kharochan's fertile fields into parched land. More than half the region's population lived below the poverty line, and thousands had left their homes for the sprawling city of Karachi.

The Indus Delta has not been struck by a natural disaster. Its plight is human-made. The Indus – the world's tenth-largest river in terms of the water it carries – has been plugged by 19 dams and is being sucked dry by 43 large canals. The Indus no longer reaches the sea in most years, and its sediments no longer replenish the delta. As a consequence, Pakistani experts told me, 8,800 square kilometers of agricultural land have been lost to the sea since dam building began.The fate of the people who are being displaced for dams in places like Pakistan, China, Brazil and India have haunted the public imagination for decades. In contrast, the people and ecosystems who suffer under the downstream impacts of large dams have often been ignored. A new scientific paper in the academic online journal Water Alternatives provides an in-depth look at the downstream impacts of large dams – impacts on ecosystems and communities that can stretch hundreds of kilometers downstream of a dam. The paper was prepared by a group of researchers around Brian Richter and Carmen Revenga of The Nature Conservancy's Global Freshwater Program, Sandra Postel of the Global Water Policy Project, Thayer Scudder, a former member of the World Commission on Dams, and Bernhard Lehner of McGill University.

No Fish, No Food

Rivers, floodplains and deltas feed hundreds of millions of people by sustaining fisheries, flood recession agriculture, and dry-season grazing land. As the Millennium Ecosystem Assessment has found, floodplains are among the most productive ecosystems on Earth. Rivers and floodplains also nurture riverine and mangrove forests, recharge groundwater resources, and provide the silt which protects deltas from being eaten away by coastal erosion.

Today about 50,000 large dams block the arteries of the planet. They have stopped fish from migrating, withheld nutrients from floodplain ecosystems and agriculture, dried up wells and riverine forests, and left deltas exposed to saltwater intrusion and erosion. The new paper presents numerous case studies for these impacts. After the Tucurui Dam was built on the Tocantins in Brazil, the fish catch immediately fell by 60 percent, affecting tens of thousands of people. The fish yields in the wetlands of Cameroon's Logone River fell by 90 percent after the Maga Dam was built. Similar impacts have been documented for dams on Ghana's Volta, Thailand's Mun and West Africa's Senegal River.

An estimated 40-80 million people have been displaced by dams. Reservoir refugees are usually entitled to compensation for their losses. Most downstream-impacted people don't have any such rights. The people who were displaced by the World Bank's Tarbela Dam in Pakistan received new homes on the banks of the reservoir and financial compensation. Yet the people who lost their homes to the sea because of the dam's downstream impacts cannot claim any compensation under Pakistan's laws or the World Bank's safeguard policies. The Bank argues that the degradation of the Indus Delta is

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