|
| volume_ref = | residence_time = 7.2 years | salinity = | shore = 3,057 km (1,900 mi) | shore_ref = | elevation = | elevation_ref = 〔 | cities = | website = }} Lake Powell is a reservoir on the Colorado River, straddling the border between Utah and Arizona (most of it, along with Rainbow Bridge, is in Utah). It is a major vacation spot that around 2 million people visit every year. It is the second largest man-made reservoir by maximum water capacity in the United States behind Lake Mead, storing of water when full. However, due to high water withdrawals for human and agricultural consumption, and because of subsequent droughts in the area, Lake Powell is currently larger than Mead in terms of volume of water currently held, depth and surface area. Lake Powell was created by the flooding of Glen Canyon by the Glen Canyon Dam, which also led to the creation of Glen Canyon National Recreation Area, a popular summer destination. The reservoir is named for explorer John Wesley Powell, a one-armed American Civil War veteran who explored the river via three wooden boats in 1869. In 1972, Glen Canyon National Recreation Area was established. It is public land managed by the National Park Service, and available to the public for recreational purposes. It lies in parts of Garfield, Kane, and San Juan counties in southern Utah, and Coconino County in northern Arizona. The northern limits of the lake extend at least as far as the Hite Crossing Bridge. A map centered at the confluence of the Escalante River with the Colorado River gives a good view of the extent of the lake. Lake Powell is a water storage facility for the Upper Basin states of the Colorado River Compact (Colorado, Utah, Wyoming, and New Mexico). The Compact specifies that the Upper Basin states are to provide a minimum annual flow of to the Lower Basin states (Arizona, Nevada, and California). ==History== In the 1940s and early 1950s, the U.S. Bureau of Reclamation planned to construct a series of Colorado River dams in the rugged Colorado Plateau province of Colorado, Utah, and Arizona. Glen Canyon Dam was born of a controversial damsite the Bureau selected in Echo Park, in what is now Dinosaur National Monument in Colorado. A small but politically effective group of objectors led by David Brower of the Sierra Club succeeded in defeating the Bureau's bid, citing Echo Park's natural and scenic qualities as too valuable to submerge. By agreeing to a relocated damsite near Lee's Ferry between Glen and Grand Canyons, however, Brower did not realize what he had gambled away. At the time, Brower had not actually been to Glen Canyon. When he later saw Glen Canyon on a river trip, Brower discovered that it had the kind of scenic, cultural, and wilderness qualities often associated with America's national parks. Over 80 side canyons in the colorful Navajo Sandstone contained clear streams, abundant wildlife, arches, natural bridges, and numerous Native American archeological sites. By then, however, it was too late to stop the Bureau and its commissioner Floyd Dominy from building Glen Canyon Dam. Brower believed the river should remain free, and would forever after consider the loss of Glen Canyon his life's ultimate disappointment. Construction on Glen Canyon Dam began with a demolition blast keyed by the push of a button by President Dwight D. Eisenhower at his desk in the Oval Office on October 1, 1956. The first blast started clearing tunnels for water diversion. On February 11, 1959, water was diverted through the tunnels so dam construction could begin. Later that year, the bridge was completed, allowing trucks to deliver equipment and materials for the dam, and also for the new town of Page, Arizona. Concrete placement started around the clock on June 17, 1960. The last bucket of concrete was poured on September 13, 1963. Over 5 million cubic yards (4,000,000 m³) of concrete make up Glen Canyon Dam. The Dam is 710 feet (216 m) high, with the surface elevation of the water at full pool being approximately 3700 feet (1100 m). Construction of the Dam cost $155 million, and 18 lives were lost in the process. From 1970 to 1980, turbines and generators were installed for hydroelectricity. On September 22, 1966, Glen Canyon Dam was dedicated by Lady Bird Johnson. Upon completion of Glen Canyon Dam on September 13, 1963, the Colorado River began to back up, no longer being diverted through the tunnels. The newly flooded Glen Canyon formed Lake Powell. It took 11 years for the lake to rise to the high-water mark, on June 22, 1980. Since then the lake level has fluctuated considerably depending on the seasonal snow runoff from the mountains. Colorado River flows have been below average since the year 2000, leading to lower lake levels. In the winter of 2005 (before the spring run-off) the lake reached its lowest level since filling, an elevation of above sea level, which was approximately below full pool (elevation 3700'). Since 2005 the lake level has risen , to a high elevation of above sea level in spring/early summer 2008. However, 2011 saw the third largest June and the second largest July runoff since the closure of Glen Canyon Dam, and the water level peaked at nearly on July 30. Water year 2012 (which started October 1, 2011) has been the extreme opposite of 2011. The huge runoff in 2011 raised the lake over 50 feet from May to July. In water year 2013, Lake Powell experienced a second consecutive year of low inflows, with only a brief period of refill in late May and June pushing the lake level up 5 feet before outflows again began outpacing inflows. In 2014, despite near-average runoff, the Bureau of Reclamation reduced for the first time the annual release from Lake Powell to Lake Mead, from 8.23 to 7.48 million acre-feet, in order to help recover levels at Lake Powell for power generation. This resulted in Lake Mead declining to the lowest level on record since the 1930s. 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「Lake Powell」の詳細全文を読む スポンサード リンク
|