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The Akosombo Dam, also known as the Akosombo Hydroelectric Project, is a hydroelectric dam on the Volta River in southeastern Ghana in the Akosombo gorge and part of the Volta River Authority. The construction of the dam flooded part of the Volta River Basin, and led to the subsequent creation of Lake Volta. Lake Volta is the largest man-made lake in the world by surface area. It covers , which is 3.6% of Ghana's land area. With a volume of 148 cubic kilometers Lake Volta is the world's third largest man-made lake by volume, the largest being Lake Kariba which is located between Zimbabwe and Zambia in Southern Africa and contains 185 cubic kilometers of water. The primary purpose of the Akosombo Dam was to provide electricity for the aluminium industry. The Akosombo Dam was called "the largest single investment in the economic development plans of Ghana."〔 Its original electrical output was , which was upgraded to in a retrofit project that was completed in 2006. The flooding that created the Lake Volta reservoir displaced many people and had a significant impact on the environment. == History == The dam was conceived in 1915 by geologist Albert Ernest Kitson, but no plans were drawn until the 1940s.〔http://www.thestatesmanonline.com/pages/news_detail.php?newsid=8696§ion=1 http://www.thestatesmanonline.com/pages/news_detail.php?section=9&newsid=9224〕 The development of the Volta River Basin was proposed in 1949, but because there were insufficient funds, the American company Volta Aluminum Company (Valco) loaned money to Ghana so that the dam could be constructed. Kwame Nkrumah adopted the Volta River hydropower project. The final proposal outlined the building of an aluminum smelter at Tema, a dam constructed at Akosombo to power the smelter, and a network of power lines installed through southern Ghana. The aluminum smelter was expected to eventually provide the revenue necessary for establishing local bauxite mining and refining, which would allow aluminum production without importing foreign alumina. Development of the aluminum industry within Ghana was dependent upon the proposed hydroelectric power.〔 The proposed project's aluminum smelter was overseen by the American company, Kaiser Aluminum, and is operated by Valco. The smelter received its financial investment from Valco shareholders, with the support of the Export-Import Bank of Washington, D.C. However, Valco did not invest without first requiring insurances from Ghana's government, such as company exemptions from taxes on trade and discounted purchases of electricity. The estimated total cost of the project, in its entirety, was estimated at $258 million.〔 In May 1960, the Ghana government called for tenders for construction of the hydroelectric dam. In 1961 an Italian consortium, Impregilo which had just completed the Kariba Dam, won the contract. They carried out the dredging of the river bed, dewatering of the channel and completed the dam a month earlier than scheduled despite flooding of the Volta River in 1963 which delayed work for over three months. Between 1961 and 1966, 28 workers of Impregilo died during the construction of the dam. Memorials in Akosombo township and St. Barbara Catholic Church have been put up in their honor. In 1961, the Volta River Authority (VRA) was established by Ghana's Parliament through the passage of the Volta River Development Act. The VRA's fundamental operations were structured by six Board members and Kwame Nkrumah as chairman. The VRA's primary task is to manage the development of the Volta River Basin, which included the construction and supervision of the dam, the power station and the power transmission network. The VRA is responsible for the reservoir impounded by the dam, the fishing within the lake, lake transportation and communication, and the welfare of those surrounding the lake.〔 The dam was built between 1961 and 1965. Its development was undertaken by the Ghanaian government and funded 25% by the International Bank for Reconstruction and Development of the World Bank, the United States, and the United Kingdom.〔(Commonwealth Education )〕 The construction of the Akosombo dam resulted in the flooding of part of the Volta River Basin and its upstream fields, and in the creation of Lake Volta which covers 3.6% of Ghana's total land area.〔 Lake Volta was formed between the years of 1962 and 1966, and necessitated the relocation of about 80,000 people, that represented 1% of the population. People of 700 villages were relocated into 52 resettlement villages two years prior to the lake's completion; the resettlement program was under the direction of the VRA.〔〔〔 Two percent of the resettlement population were riparian fishers and most were subsistence farmers.〔 The Eastern Region of Ghana and the populations incorporated within its districts, were most subject to the project’s effects. In the beginning of 2007, there were concerns over the electricity supply from the dam due to low water levels in the Lake Volta reservoir.〔(【引用サイトリンク】title=Akosombo Dam To Be Shut Down? )〕 Some sources said this was due to problems with drought that are a consequence of global warming.〔(【引用サイトリンク】title=Politics of Akosmobo Dam in Ghana )〕 During the latter half of 2007 much of this concern was abated when heavy rain fell in the catchment area of Volta River.〔(【引用サイトリンク】title=Flood destroys farmlands in Bongo District )〕 In 2010 the highest ever water level was recorded at the dam. This necessitated the opening of the flood gates at a reservoir elevation of , and for several weeks water was spilled from the lake causing some flooding downstream.〔(【引用サイトリンク】url=http://www.ghanaweb.com/GhanaHomePage//economy/artikel.php?ID=198319 )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Akosombo Dam」の詳細全文を読む スポンサード リンク
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