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.
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.
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 "part of the bargain struck in order to support large numbers of people in the Indus Basin." In other words, some people have to suffer so that others can prosper.
Dams contribute to about 12-16 percent of the world's food production, and generate 19 percent of the world's electricity. As in the case of Pakistan, dam builders have often maintained that these benefits compensate for the losses of downstream communities. Yet downstream impacts can extend far beyond the reach of reservoir fisheries and irrigation, and can outweigh the benefits of dams. The new study presents case studies for this. While large, deep reservoirs yield an average of 10-50 kilogram fish per hectare and year, floodplain fisheries yield an average of 200-2000 kilogram per hectare and year. Scientific studies have also found that even without considering the cost of building a dam, the economic value of floodplains may be higher than the value of irrigated land.
As part of their research, the authors of the new paper created a database of case studies about the downstream impacts of dams. Their database covers more than 120 rivers in at least 70 countries. The researchers created a separate database of all rivers which have at least one tenth of their annual water discharge stored by the world's 7,000 largest dams. By using a geographic information system, they calculated that the downstream impacts of dams on these rivers have probably negatively affected at least 472 million people. Of these, 400 million live in Asia. By cross-referencing their calculation with specific case studies, they found that their estimate is likely to be conservative.
Richter and his co-authors conclude "that dam development projects aimed at reducing poverty or improving economic opportunities are benefiting many but are also deepening poverty and hunger for others. The failure to adequately account for these impacts precludes an honest rendering of the net costs and benefits of dams." They argue that "a sizeable proportion of the human population is being fed by the natural productivity of river ecosystems," and "that it does not make sense to continue to damage these natural life-support systems when far less destructive approaches to dam development are readily available."
The authors put forward a series of practical recommendations that could help to take downstream impacts of large dams into account. They make the case for an integrated planning approach to whole river basins, to prevent dams from being built in the wrong places. Integrated river basin planning takes social, environmental and economic costs and benefits into account, and includes the evaluation of rivers' current benefits through participatory assessments. The authors also call for dam design and operational plans which strike an optimum balance between economic, social and environmental benefits -- for example, through providing adequate environmental flows -- and which are continuously monitored and adapted.
A successful example for the authors' approach is the relicensing agreement between a power company, the Penobscot Indian Nation and environmental NGOs regarding hydropower plants on the Penobscot River in the Northeastern US. Under this agreement, two dams will be removed and the fish passage on another dam was improved. Even so, the total power generation from the dams on the river will be maintained or slightly increased through the rehabilitation of the remaining power plants.
From a personal perspective I will add that it is no longer acceptable to sacrifice the interests of one population group for the benefit of another in a supposed "bargain" struck by powerful elites. Like other affected people, downstream-impacted communities should have the right to participate in the decision-making process over projects that affect them, and should be entitled to full compensation of their losses if indeed a dam is built. If all costs and benefits of water and energy options are considered in a balanced assessment, less destructive solutions than large dams will be found in many cases.
Brian D. Richter, Sandra Postel, Carmen Revenga, Thayer Scudder, Bernhard Lehner, Allegra Churchill, Morgan Chow: Lost in development's shadow, The downstream human consequences of dams, in: Water Alternatives 3(2), June 2010: pp. 14-42
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