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How much water is 29 [km.sup.3]? It is hard to imagine, and even harder when expressed in gallons (or liters), as 7,660,989,081,241 gal (29,000,000,000,000 liters). A compromise would be to imagine it as 29 thousand million cubic meters of water, or 29,000 [hm.sup.3]. This is the amount of water present in a sheet of water 3.3 ft (1 m) tall covering an area of 11,197 mi2 (29,000 [km.sup.2]). And it is the amount of water in Itaipu reservoir, located in the heart of the Mission forest, and the largest reservoir in the world built to generate hydroelectricity.

This colossal hydroelectric scheme is fed by the rain falling on a watershed of 316,602 mi2 (820,000 [km.sup.2]). It is located on the Parana River, above its confluence with the Iguazu River. The Parana's flow is between 321,000 ft3 (9,100 [m.sup.3]) and 1,165,000 ft3 (33,000 [m.sup.3]) per second, depending on the time of year. The dam is an impressive 607 ft (185 m) tall, a wall of 424 million ft3 (12 million [m.sup.3]) of reinforced concrete, and the reservoir covers 1,350 [km.sup.2]. The discharge capacity is 2,197,667 ft3 (62,231 [m.sup.3]) per second.

The 18 Francis turbines of this colossal dam generate a total of 79,000 GWH, with an installed potential of 12,000 MW. This is just one of the 41 hydroelectric installations in the Brazilian area of the Parana's watershed, where there are another 17 projects for its largest tributaries: the Paranaiba, Grande, Tiete, Sucuriu, Paranepanema, and Ivai. Building large dams has been one of the main features of Brazil's development policies since the 1960s, when Brazil started to systematically build taller and taller dams retaining larger and larger volumes of water, and larger and larger reservoirs (such as Furnas, Graminha, Emborcacao, Sobradinho).

The prevailing model of development in Brazil in the 1960s implied high demand for electricity, at a time when the country was importing 85% of the oil it consumed. The availability of abundant water resources suitable for producing electricity, led the planners to try and make use of them. On June 22, 1966, the foreign ministers of Brazil and Paraguay signed the Act of Iguazu, in which they agreed to jointly study the water resources along the frontier between the two countries, from Salto das Sete Quedas, and Salto de Guaira (the name given to a series of 18 cascades), to the mouth of the Iguazu River. In the late 1970s, feasibility studies began on the Itaipu dam, and construction began in 1975. The reservoir started to fill in November 1982.

The Itaipu dam has had an enormous impact in both Brazil and Paraguay. The main economic activities of the cities of Foz de Iguazu (Brazil) and Ciudad del Este (Paraguay), trade and tourism, grew spectacularly, and Foz de Iguazu increased from 3,829 inhabitants in 1960 to about 120,000 in 1980. This was greater than the increase in the transitory population engaged in building the dam and the associated activities. Part of the Brazilian municipalities of Guaira, Terra Roxa, Marechal Candido Rondon, Santa Helena, Matelandia, Medianeira, Sao Miguel do Iguazu, and Foz have disappeared under the waters, and the infrastructure and communication routes of the remaining areas have been disrupted. The urban areas, which occupied 1,053 acres (426 ha) in 1973, soon occupied about 13,838 acres (5,600 ha).

The area's organization had previously followed a dominant N-S axis along the Parana River, but adopted an east-west orientation, which was later strengthened by the creation of Merco-sur. This change was due to the change from an economy based on small peasant units producing for the internal market to an export-oriented economy based on intensive production by agricultural companies that only required a small labor force, and thus provided little employment for the rural popu-lation. This new axis connects the agricultural areas of Paraguay to the Brazilian port of Paranagua.

Itaipu's greatest impact has been on the environment. The 43 mi (70 km) long reservoir flooded a national park and the wonderful Salto das Sete Quedas waterfalls. Before the area was flooded, 145,000 objects relating to the Vinitu culture (8,000 years old), Pirajui culture (3,000-6,000 years ago), Aipacairi (5,000 years ago), Itacora, Ibiraje, Cantu, Sarandi, Icaraima, and Assuna cultures were removed from 210 archeological sites identified between 1975 and 1981. An enormous area of forest and agricultural land was also destroyed, and they represented a huge input of organic matter into the reservoir (about 4.4 million short tons [4 million tonnes] of plant biomass).

The forests flooded by the waters contained more than 600 different plant species, some of them commercially valuable trees, such as ipes (Tabebuia), peroba or yvyra ro'mi (Aspidosperma polyneuron), and pau marfim, guatumbu, or yvyra neti (Balfourodendron riedelianum). There were thousands of trees more than 16 in (40 cm) in diameter, and there was a volume of wood of 24-33 [m.sup.3]/ha. The populations of more than 70 species of mammal, belonging to 22 different families, and including the lowland tapir (Tapirus terrestris) and several species of cat, suffered notable losses. Without trying to be exhaustive 252 species of bird were affected, belonging to 54 different families, and about 1,600 species of insect, belonging to 19 different orders, and 23 different species of reptile.

Itaipu, like all reservoirs, will eventually silt up. Every year it traps 13.7 million short tons (12.5 million tonnes) of sediments. However, it will take several centuries for Itaipu to completely silt up. And 311 mi (500 km) downstream, there is another hydroelectric dam on the Parana River, the Yacyreta-Apipe Dam, on the frontier between Paraguay and Argentina, which is just as spectacular as Itaipu, and which has a capacity of 21,000 [hm.sup.3] and covers 618 mi2 (1,600 [km.sup.2]) ...
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Publication:Encyclopedia of the Biosphere
Geographic Code:1USA
Date:Jun 1, 2000
Previous Article:Botany Bay.
Next Article:4 The protected areas and biosphere reserves in the temperate rainforests.

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