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Auburn Dam was a proposed dam on the North Fork of the American River east of the town of Auburn, California in the United States, on the border of Placer and El Dorado Counties. Slated to be completed in the 1970s by the U.S. Bureau of Reclamation, at a height of the concrete arch-gravity dam was to be the largest three-centered thin arch dam in the world. Straddling a gorge downstream of the confluence of the North and Middle Forks of the American River and upstream of Folsom Lake, it would have regulated water flow and provided flood control in the American River basin as part of Reclamation's immense Central Valley Project. Proposals and studies for the dam emerged in the late 1960s, and construction work commenced in 1968, involving the diversion of the North Fork American River through a tunnel and the construction of a massive earthen cofferdam. Following a nearby earthquake and the discovery of a seismic fault that underlay the dam site, work on the project was halted for fears that the dam's design would not allow it to survive a major quake on the same fault zone. Although the dam was redesigned and a new proposal submitted by 1980, spiraling costs and limited water storage offered by either design put an end to the project until heavy floods destroyed the cofferdam, sparking brief renewed interest in the dam. The California State Water Resources Control Board denied water rights for the dam project in 2008 due to lack of implementation. Although new proposals surfaced from time to time after the 1980s, the dam was never built for a variety of reasons. Limited flood-control capability, geologic instability, and potential harm on recreational and ecological values finally put an end to the Auburn Dam project. Many of the original groundworks and preliminary constructions at the Auburn Dam site still exist, and up to 2007, the North Fork American River still flowed through the diversion tunnel that had been constructed in preparation for the dam. Reclamation and Placer County Water Agency completed a pump station project that year which blocked the tunnel, returned the river to its original channel, and diverted water through another tunnel under Auburn to meet local needs. However, some groups continue to support construction of the dam, which they claim would provide important water regulation and flood protection. ==Early history== In the 1850s, the city of Sacramento was rapidly growing around the confluence of the Sacramento River and its tributary the American River, near the middle of the Central Valley of California. The city's increasing population necessitated the construction of an extensive system of levees on the two rivers to prevent flooding, especially on the American. The flood control works were not enough to keep the rivers within their beds, however; in 1862, the city was inundated so completely that the state government was temporarily moved to San Francisco. In 1956, the U.S. Army Corps of Engineers built the Folsom Dam on the lower American, near the confluence of its North and South Forks, to provide flood control for the Sacramento metropolitan area. However, the Folsom Dam provided inadequate flood storage, and overflowed on several occasions since its construction. In fact, a flood in 1955 filled the Folsom Reservoir to capacity, before the dam was even completed.〔Smith, p. 29〕 Water demand in the Central Valley in the Sacramento area was also growing, mainly for agricultural usage. In 1854, a diversion dam was constructed on the North Fork American River at the site of Auburn Dam, to divert water into a series of ditches that supplied irrigation water for downstream farms. Irrigation with dam and canal systems was favored because severe flow fluctuations in Central Valley rivers created floods in some years and droughts in others.〔Smith, p. 28〕 It was in this light that the Auburn Dam was first contrived. As early as the 1950s, plans for a giant dam at the Auburn site were already being considered, in the name of flood control. Several designs, both earthfill and concrete, were considered. Before the dam could be built, however, the Auburn-Foresthill Road, which crossed the river just upstream of the dam site, had to be relocated. Even before the project was authorized, several companies had already taken contracts for the construction of a high bridge to carry the road over the proposed reservoir and preliminary excavations at the dam site.〔 Auburn Dam was to be a massive flood-control and storage structure on the North Fork of the American River, just upstream from Folsom Reservoir. It would create a reservoir with more than twice the capacity of Folsom, which could help reduce floods on the American.〔The capacity of Folsom Lake is just under ; Auburn Reservoir would have stored of water at full pool〕 With the introduction of the Central Valley Project in the mid-1930s, came the Auburn-Folsom South Unit, with the purpose to "provide new and supplemental water for irrigation, municipal and industrial use, and to replenish severely depleted ground water in the Folsom South region".〔 In 1965, Congress authorized the Auburn-Folsom South Unit of the Central Valley Project, the primary feature of which was to be Auburn Dam.〔 The targeted completion date was 1973. As the proposals for the Auburn Dam evolved, the project saw a transformation from a purely flood-control structure to a multipurpose high dam that would serve various purposes including storage, hydroelectricity generation, and recreational activities. One of the first ideas, publicized in the late 1950s, called for a embankment dam impounding of water. In 1963, a earthfill dam holding back of water was proposed.〔 The pre-construction design was finalized in 1967, for a concrete thin-arch gravity structure over high.〔 This dam would be long, thick at the base, and equipped with five 150MW generators at its base for a total generating capacity of 700 MW. Two concrete-lined flip bucket spillways would abut both sides of the dam. Construction work for the dam started in late 1968.〔 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「Auburn Dam」の詳細全文を読む スポンサード リンク
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