Dams provide benefits in water management in the following ways: (1) They conserve water by storing it in reservoirs; (2) they supply irrigation water; and (3) they reduce flooding downstream. In addition, many dams have been built for the main purpose of producing electricity. All of these factors have helped preserve people’s property, and the waterpower from dams serves as a sustainable energy source.
Dams conserve water in two ways: Reservoir water behind dams serves as low-cost storage for a community’s drinking supply, and the downstream flow provides a constant source of irrigation water. Both situations conserve groundwater. Lakes behind dams provide outdoor recreation areas and places for fishing, perhaps sparing wilderness areas from excess human activities. For each of these positives, however, there is also a disadvantage, summarized in the table below.
When dams interfere with natural water flows, they affect aquatic ecosystems that live in riparian habitats. Dams do this by changing the normal flow of sediments that carry nutrients to microbes and invertebrates, taking away long stretches of running water that some migrating fish need, and slowing water flow enough to allow salt water from estuaries to move upstream. Salt water contamination kills the diverse microbes, invertebrates, amphibians, fish, and plants that need freshwater.
Two opposing schools of thought have grown regarding the role of dams in the environment today, and not surprisingly, the arguments become contentious. Butch Hopkins of California’s Reclamation Board explained the major issue swirling around the American River’s Auburn Dam to the Sacramento Bee in 2006: “The dam is incredibly controversial because it runs flat into the fundamental beliefs of fiscal conservatives and environmentalists.” Those words describe almost all large dam projects in place today.
Dams allow communities to take advantage of a renewable energy source while they also practice water conservation. But environmentalists have called for the removal of large and small dams, and in the past few decades many dams have in fact come down, either because they had become dangerously degraded or because they were part of a riparian restoration. Three environmental groups—Friends of the Earth, Trout Unlimited, and American Rivers—published a report together in 1999 that detailed case studies of dam removal projects. Dam Removal Success Stories summarized the rationale behind dam removal: “Even for some functioning dams, removal may be a sound solution when a dam’s benefits are outweighed by the significant environmental damage it causes. . . . Clearly dam removal is not appropriate for all—or even most—of the nation’s 75,000 large dams. Many dams continue to serve public or private functions such as flood control, irrigation, and hydropower generation.” But for dams that have a clear and devastating effect on the environment, their removal helps restore riparian habitat. The report said of dam removal: “Dams all across the country have been or are in the process of being removed for three primary reasons: environmental, safety, and economic. Most removal decisions involve a combination of all three of these reasons.” Thousands of small dams remain in the United States in areas that at one time supported farming or logging.
Proponents and opponents have come to an uneasy truce regarding hydroelectric dams, meaning dams that produce electricity. Hydroelectric power replaces the need for coal-burning power plants, so these dams receive support from many people in the public and in government. John Doolittle, who served in the California House of Representatives
during the time a dam was planned for the town of Auburn, stated in 2006, “Any dam will eventually pay for itself. If you build a multipurpose dam, it’s a moneymaking machine because it generates the sale of electricity and of water.” At present, people continue to weigh the advantages of dams against the disadvantages. The sidebar “Three Gorges Dam” explores one of the world’s most famous and controversial dam projects.
Source of Information : Green Technology Conservation Protecting Our Plant Resources
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