Dams Essay ⋆ Environment Essay Examples ⋆ EssayEmpire

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Few technologie s have had more significant and persistent ecological impacts than dams. Almost every major river in the world has at least one large dam obstructing its flows. China alone has built over 22,000 large dams on rivers within its national territory, most of which have been constructed over the past three decades, and is nearing completion of the largest human-made structure in the world, the Three Gorges Dam. While varying in size and type, all dams share the goal of obstructing the flowing water of a river or stream in order to provide an array of perceived benefits to human communities. The most important of these include the conversion of flowing water into electricity (hydropower), the storage of water for irrigated agriculture, and the control of floods. Dams also engender an array of social and environmental consequences. Depending on size and location, dams create reservoirs, cause massive displacements of people, block fish migration routes, and significantly alter the hydrology and ecology of flowing rivers.

While the construction of dams to divert or block a river’s flows is a technology dating back 5,000 years, the 20th century witnessed an unparalleled expansion in the scope and size of impoundments. The construction of Hoover Dam, a 220 meters high hydroelectric project built on the Colorado River in the western United States in the 1930s, ushered in the era of large dams. Over 40,000 large dams-defined as those with height of 15 meters or more have been constructed on the world’s rivers, the vast majority since 1950. In total, the water stored behind dams in reservoirs amounts to 10,000 cubic kilometer (roughly five times all the volume of the world’s rivers combined) and covers an estimated land area of 400,000 square kilometers (about the size of California). There are three primary types of impoundments-embankment, gravity, and arch dams-that are designed based on the local geology and topography of a dam site. Most dams (80 percent) are earth and rock embankments, typically built across wider river valleys where dam fill materials are readily available.

As the scale of a dam increases, the scope, duration, and intensity of its social and environmental impacts also become amplified. The largest dams-such as the massive Itaipu impoundment on the Parana River in South America, the Columbia River’s Grand Couleee in the western United States, the Volga’s Kuibyshev Dam in the Russian state of Samara, the Volta’s huge Akosombo Dam in Ghana and, most recently, the Three Gorges Dam on the Yangtze River in China-have collectively displaced millions of people, inundated thousands of hectares of land, and brought about host of other socioecological effects. However, numerous dams and accompanying systems of weirs, barrages, and levies have for centuries served important roles in flood control, enhanced agricultural production, and urban water supply in nearly every region of the world.

In terms of human-environment relations, it is difficult to separate dams’ social and ecological impacts. Both are closely intertwined, especially in those regions of the world where people remain partly or wholly dependent on the resources conferred by unobstructed rivers. In the equatorial zones such as the Amazon and Congo Basins and parts of monsoonal Asia such as the Mekong basin, millions of livelihoods remain crucially dependent on freshwater fisheries and floodplain agriculture, practices whose sustainability and integrity are in turn intimately linked to annual riverine flow cycles. The social and biophysical impacts of dams, particularly larger dams that produce significant reservoirs of stored water, can be usefully organized into (1) those effects experienced primarily near the dam site, the dam’s reservoir, and related upstream regions, and (2) those effects experienced primarily downstream of the dam, oftentimes extending to a river’s delta and estuarine regions.

An initial and obvious impact of river impoundment is the inundation of vast hectares of riverine lands and the consequent displacement of people living in these areas. While state agencies in charge of dam construction often pledge dam-affected peoples compensation in the form of new housing structures, agricultural lands, and cash payments, numerous relocation programs throughout Africa, Asia, and Latin America have failed to deliver on promised compensation plans. official resettlement areas are typically inferior to traditional riverine lands in terms of agricultural productivity, and the long-term inhabitants living in these areas resent displaced peoples. This was the experience of the more than 100,000 Nubians resettled due to construction of the Aswan High Dam on the Nile River. The resettlement communities lacked basic amenities, exposed the displaced people to new diseases, and were agriculturally inferior to their previous lands.

A reservoir also represents a radical alteration of a river’s hydrological and ecological functioning. While retaining some of the biophysical characteristics of a river, a reservoir essentially causes a shift from a flowing to a standing water environment. The shift from flowing water to largely stagnant water results in a host of hydrological, biological, chemical, and ecological transformations. Levels of dissolved oxygen and other key water chemistry parameters are irrevocably altered within reservoirs. The species composition and numbers of fish and other aquatic organisms shift to reflect a more lake-like ecosystem, resulting in the drastic reduction or extirpation of those species adapted to riverine environments. Dams can virtually eliminate migratory fish species whose routes from ocean to spawning grounds are blocked. The annual run of adult salmon and steelhead trout in the Columbia River Basin in the United States’ northwest region has declined from a population of 10-16 million in the mid-19th century to an estimated 1.5 million in 2006, due almost entirely to the basin’s 130 dams. France’s runs of Atlantic salmon on many of its rivers suffered a similar fate due to dams built throughout the latter19th century.

In many tropical reservoirs, such as Lake Kariba on the Zambezi River in southern Africa, invasive or undesirable plant species such as the water hyacinth and giant salvinia have proven difficult to manage. In addition, the filling of a reservoir after dam construction, which can take any where from several months to two or more years before completion, can have serious ecological consequences in terms of habitat destruction. In the case of the Kariba and Cahora Bassa dams on the Zambezi River in southern Africa, built in the late 1950s and early 1970s, respectively, dam authorities and governments undertook efforts to capture and relocate indigenous fauna (particularly large mammal species) prior to inundation, but numerous animals drowned during the filling period.

Reservoirs also produce economic and recreational benefits for some social groups. In the western United States, for example, massive reservoirs on the Colorado River (such as Lake Mead and Lake Powell) are important sites of recreational activity such as sport fishing and boating. Dams and reservoir levels are frequently managed to allow for downstream recreational activities such as rafting. In many tropical areas, the damming of flowing waters has resulted in very productive reservoir fisheries. However, many of these fisheries have proven a mixed blessing to local communities. At the Ubolratana reservoir in Northeast Thailand, constructed primarily as a hydroelectric facility in the 1960s, a lack of management and unsustainable harvesting rates have led to over fishing and relative poverty for reservoir communities dependent on fisheries for their livelihoods.

The water storage functions of dams also engender a host of social and ecological consequences, particularly impoundments designed to promote irrigation development. Throughout the 20th century, numerous governments-particularly those presiding over arid regions-perceived dams’ water storage function as a crucial means of promoting irrigated agriculture and, eventually, boosting agricultural production. Massive investments in irrigation systems-consisting of a series of smaller weirs, barrages, and channels downstream of the primary impoundment to divert water to nearby agricultural lands-accompanied the so-called Green Revolution in agriculture in much of the Third World in the 1960s and 1970s. While the result of these investments has in many areas boosted overall agricultural production, irrigation development has also contributed to environmental degradation and social disruption.

One of the most serious environmental impacts of irrigation systems is salinization, or the increased presence of salts in agricultural soils associated with irrigated agriculture. The evaporation of water from reservoirs, canals, and fields can lead to increased concentrations of salts in irrigation water, which in turn increase the risk of adding salts to farming areas. Farmers often deliver more irrigation water to flush out saline soils, but this runs the risk of increasing the salinity of ground water. If improperly drained-poor drainage has been a dilemma for irrigated agriculture for decades-salts tend to accumulate in the groundwater below agricultural fields, adding to the problem. Saline water from irrigated fields, when returned to river channels, also contributes to degraded water quality in downstream reaches. Salinization has plagued the extensive irrigation systems built first by the British and later expanded by post-independence governments in northwestern India.

In addition, dams and irrigation systems often create favorable conditions for the genesis and spread of vectors (such as snails or insects) for debilitating diseases like schistosomiasis and malaria. Increased incidence of both diseases, which have a direct impact on human health and indirect economic impacts in terms of reduced labor availability, has followed the construction of water development infrastructure in many parts of North and West Africa, south Asia, and southeast Asia. Among communities living near the gigantic Volta Reservoir in Ghana, rates of people infected with urinary schistosomiasis skyrocketed in the years immediately following construction of the Akosombo Dam in 1965.

State-sponsored irrigation projects typically demand a series of reforms in the way that agricultural production is organized and managed. Irrigated agricultural demands an entirely different set of practices and technologies than rain-fed agriculture, and recipient communities are typically ill prepared to adopt these new techniques. Furthermore, the expenses associated with training farmers in new techniques and maintaining functioning irrigation infrastructure frequently outweigh the economic benefits associated with such projects. Such has been the case with numerous large-scale irrigation schemes such as the Mahaweli project in Sri Lanka, the arid regions of northern Mexico, and Kenya’s Bura irrigation project on the Tana River.

While the impoundment of rivers generates significant biophysical changes in the area immediately upstream of the dam site, downstream hydrologic and ecological alterations are equally significant. Dams, by removing the fine and coarse sediment normally transported by flowing rivers, often result in significant morphologic adjustments to the river channel. The increased scouring of sediment-free waters can lead to downstream bank erosion and ultimately, to changes in river channel morphology, gradient, and sinuosity. Dams’ blockage of sediment and nutrient flows can also significantly alter downstream water quality. Depending on factors such as the location where water is extracted and delivered to the channel below a dam and the relative volume of flows allowed downstream, a dam can produce major effects on river temperature, concentration of heavy metals and minerals, dissolved oxygen and other gases, turbidity, and nutrient load.

Perhaps most significant in terms of human-environment relations, dams can profoundly alter the timing, duration, and magnitude of seasonal flooding. In those regions where floodplains constitute important sites of agricultural and fisheries production, in particular the tropical and monsoonal zones of Asia, Africa, and Latin America, the disruption of annual flooding cycles has disrupted farming schedules, dried out floodplain forest ecosystems, and destroyed important fish habitats. Formerly productive floodplains that provided fish, plant materials, and other economically important resources to nearby communities in the southern United States’ Mississippi River Delta, have been devastated as a result of upstream water projects.

Large dams can also have significant impacts on the delta and estuarine regions of a river system. In estuaries, many aquatic species have adapted to specific salinity gradients where the fresh water of the flowing river meets the tidally influenced saline water of the ocean. Moreover, numerous marine species depend on the tremendous amount of nutrients delivered by rivers to their estuaries. Dams cut off this important food source. Egypt’s productive sardine fishery-dependent on annual plankton blooms spurred by floods that brought nutrients to the mouth of the Nile-in the Mediterranean Sea went into a precipitous decline in the years following closure of the Aswan Dam in the early 1970s on the Nile River.

Expressions of Power

Dams are also expressions of political, economic, and symbolic power. Dam building is a big business, with an annual expenditure of between $32 and $42 billion during the 1990s. Despite these enormous investments, many, if not a majority, of the world’s large dams constructed in the 20th century have been plagued by large cost overruns, construction delays, and unrealized economic benefits due to less than expected electricity production or water storage capacity. Beyond their potential economic benefits and costs, dams often serve a symbolic role, as representations of nationalism and humanity’s ability to control nature. For dam promoters and builders, they are magisterial testaments to economic development and scientific progress. Prime Minister and nationalist leader Jawaharlal Nehru famously declared in the early 1950s that dams were the “temples of modern India” that would fuel agricultural development and industrialization. Similarly, the Akosombo Dam on the Volta River in Ghana and the Cahora Bassa Dam on the Zambezi in Mozambique both became important symbols of national economic development in post-independence Africa.

Dams have emerged as important foci in local and global struggles over environmental degradation and livelihood disruption. Northern-based nongovernmental organizations (NGOs) such as the U.S.-based International Rivers Network (IRN) and the Canada-based Probe International have formed coalitions with numerous NGOs and people’s organizations across the globe to oppose a host of specific dam projects. Dam-affected peoples and their advocates have pointed out the disproportionate social and environmental costs borne by those communities whose fisheries-based and agricultural livelihoods are destroyed by the construction of large dams. These struggles culminated in the creation of the World Commission on Dams (WCD) in the late 1990s. The WCD-an organization founded by the World Bank and the World Conservation Union (IUCN) and made up of representatives from states, the dam industry, and dam critics-published a comprehensive report in 2000 calling for a more participatory approach to the construction of large dams. The report was highly critical of many of the world’s large dam projects over the past half century, noting that many had failed to achieve their stated objectives in terms of electricity generation and irrigation coverage and had resulted in profoundly negative impacts on displaced communities without providing just compensation.

Bibliography:

William Adams, Wasting the Rain: Rivers, People, and Planning in Africa (University of Minnesota Press, 1992);
Sanjeev Khagram, Dams and Development: Transnational Struggles for Water and Power (Cornell University Press, 2004);
Patrick McCully, Silenced Rivers: The Ecology and Politics of Large Dams (Zed Books, 2001);
Geoffrey Petts, Impounded Rivers: Perspectives for Ecological Management (John Wiley & Sons, 1984);
Marc Reisner, Cadillac Desert: The American West and Its Disappearing Water (Penguin, 1993);
Richard White, The Organic Machine: The Remaking of the Columbia River (Hill and Wang, 1995);
World Commission on Dams, Dams and Development: A New Framework for Decision-Making. The Report of the World Commission on Dams (Earthscan, 2000).