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New Exchequer Dam is a concrete–faced, rock-fill dam on the Merced River in central California in the United States. It forms Lake McClure, which impounds the river for irrigation and hydroelectric power production and has a capacity of more than . The Merced Irrigation District (MID) operates the dam and was also responsible for its construction. Built between 1964 and 1967, the dam replaced the old arch type Exchequer Dam and stands high. At the time of completion, it was the largest dam of its kind in the world. The dam is named for the town of Exchequer which now lies under the reservoir, while the reservoir is named for Wilbur F. McClure, the State Engineer of California during construction.〔 ==History== In 1926, after five years of planning and construction, MID completed the Exchequer or "Great Exchequer" Dam across the Merced River six miles (9.7 km) above the town of Merced Falls. The dam was a concrete gravity–arch structure high, holding a lake with a capacity of of water. Although the dam was to serve primarily for irrigation, power production began ceremoniously on June 23, 1926 with a press of a telegraph key by President Calvin Coolidge, starting the turbines at a 31 megawatt hydroelectric plant. By the 1950s, it became apparent that the limited storage capacity at Exchequer was no longer enough to serve the needs of farmers in the Merced River valley. A high dam was proposed to be built just downstream, creating a reservoir nearly four times the size of Exchequer.〔 Construction of New Exchequer Dam began on July 8, 1964, directly downstream from the old concrete arch dam.〔 Tudor Engineering Company of San Francisco was responsible for the design of the new dam. The dam wall was constructed in vertical zones, which consisted of compacted, alternating layers of coarse and fine material ranging in thickness from . The old Exchequer Dam was incorporated as an upstream toe to help support the rock-fill embankment, which was then armored with a layer of reinforced concrete. The dam was topped out in early 1967〔 and the power plant went into commercial operation by July.〔 As the new reservoir filled, it inundated an additional of the Merced River canyon and buried sections of the historic Yosemite Valley Railroad and the mining town of Bagby under of water. New Exchequer was among the first high concrete–faced rock-fill dams in the world, and its untested design resulted in significant leakage, sometimes up to . MID began to repair the leaks in the fall of 1985 under orders from the California Division of Safety of Dams. The dam has been able to halt major floods in many instances, such as the New Year's Day Flood of 1997.〔 However, it has not always been able to weather the worst droughts – such as in 1977, when the reservoir fell to just , a fourteenth of capacity,〔 and in 1991, which saw historic low water levels of . In February 2015, the reservoir reached its lowest level on record, at or less than 7 percent of total capacity, due to three years of persistent drought. 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「New Exchequer Dam」の詳細全文を読む スポンサード リンク
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