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Environment Magazine September/October 2008

 

July/August 2008

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Small Size, Big Potential: Check Dams for Sustainable Development

The Earth’s thirsty and burgeoning human population is confronted today with the reality of an unchanging freshwater supply, and the disparity between necessity and supply grows worse each year. As a result, water has emerged as one of the most important commodities of the twenty-first century, and in some areas water scarcity threatens future security.

Tensions have arisen—or have great potential to rise—between countries bordering major river basins, including the Danube in Europe; the Zambezi and Nile in Africa; the Colorado in North America; and the Mekong, Ganges, and Indus in Asia. Within nations, conflicts have emerged in Australia’s Murray-Darling basin and along the Columbia River, both in the United States and in Canada. And recently, an interstate water conflict has come to a head in South India’s Cauvery delta. Thus policymakers, scientists, and water managers all face an increasingly difficult task: determining how to meet the water and food needs of the mushrooming human population while minimizing damage to the natural environment. Complicating the issue is the profound impacts humans have had on the planet’s large rivers. By building dams, reservoirs, and diversion canals, humans have drastically changed the quantity and timing of flows—the very nature of our rivers.

Prior to 1900, only 40 reservoirs had been built that held total storage volumes greater than 25 billion gallons. However, today there are approximately 3,000 reservoirs that, taken together, hold more than 1,500 cubic miles of water, enough to flood 120 million acres of land—greater than the entire area of Cambodia. Global water use has increased sixfold during the last century, and policymakers and politicians have met this increasing demand by building larger dams. Can these megadams solve chronic water shortages, poverty, and future food security?

Proponents of megadams have argued that bigger dams are better; they reduce dependency on rainfall, increase irrigation opportunities, provide water to drought-prone areas for economic development, reduce flooding, and supply hydropower. However, opponents have found that they have caused considerable environmental damage, which includes fragmentation of riverine ecosystems, reduction of forest and agricultural land due to flooding, changes in natural flow patterns, alteration of soil erosion, loss of habitat for wildlife, and natural earthquake or reservoir-induced seismicity that may cause dam collapse and flooding.

In India alone, between 1980 and 2000, dams submerged 11.1 million acres of forest land, and about one-tenth of the area irrigated by megadams has suffered waterlogging. The social costs of spontaneous displacement are as dramatic as the ecological costs: globally, 40 to 80 million people have been forced off their lands due to dam-related flooding. Each megadam constructed in India has on average displaced 31,340 people, and nearly half of those belonged to historically underprivileged tribal people.

Evidence from semiarid regions of western India has shown that a more sustainable solution may be to build numerous check dams—small barriers using stones, cement, and concrete built across the direction of water flow on rivers to harvest rainwater in remote villages.

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