Hoover Dam

Hoover Dam, also sometimes known as Boulder Dam, is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the U.S. states of Arizona and Nevada. When completed in 1935, it was both the world's largest electric-power generating station and the world's largest concrete structure. It was surpassed in both these respects by the Grand Coulee Dam in 1945. It is currently the world's 35th-largest hydroelectric generating station.

This dam, located 30 miles (48 km) southeast of Las Vegas, Nevada, is named after Herbert Hoover, who played an instrumental role in its construction, first as the Secretary of Commerce and then later as the President of the United States. Construction began in 1931 and was completed in 1935, more than two years ahead of schedule. The dam and the power plant are operated by the Bureau of Reclamation of the U.S. Department of the Interior. Listed on the National Register of Historic Places in 1981, Hoover Dam was designated a National Historic Landmark in 1985.

To protect the construction site from flooding, two cofferdams were constructed. Construction of the upper cofferdam began in September 1932, even though the river had not yet been diverted. A temporary horseshoe-shaped dike protected the cofferdam on the Nevada side of the river. After the Arizona tunnels were completed, and the river diverted, the work was completed much faster. Once the coffer dams were in place and the construction site dewatered, excavation for the dam foundation began. For the dam to rest on solid rock, it was necessary to remove all the riverbed's accumulated erosion soils and other loose materials until sound bedrock was reached. Work on the foundation excavations was completed in June 1933. During excavations for the foundation, approximately 1,500,000 yd³ (1,150,000 m³) of material was removed. Since the dam would be a gravity-arch type, the side-walls of the canyon would also bear the force of the impounded lake. Therefore the side-walls were excavated too, to reach virgin (un-weathered) rock which had not experienced the weathering of centuries of water seepage, wintertime freeze cracking, and the heating/cooling cycles of the Arizona/Nevada desert.

To divert the river's flow around the construction site, four diversion tunnels were driven through the canyon walls, two on the Nevada side and two on the Arizona side. These tunnels were 56 feet in diameter. Their combined length was nearly 16,000 feet (4877 meters, more than three miles). Tunneling began at the lower portals of the Nevada tunnels in May 1931. Shortly afterwards, work began on two similar tunnels in the Arizona canyon wall. In March 1932, work began on lining the tunnels with concrete. First the base or "invert" was poured.

Gantry cranes, running on rails through the entire length of each tunnel were used to place the concrete. The sidewalls were poured next. Movable sections of steel forms were used for the sidewalls. Finally, using pneumatic guns, the overheads were filled in. The concrete lining is three feet (91.5 centimeters) thick, reducing the finished tunnel diameter to 50 feet (15.25 m).

Following the completion of the dam, the entrances to the two outer diversion tunnels were sealed at the opening and half way through the tunnels with large concrete plugs. The downstream halves of the tunnels following the inner plugs are now the main bodies of the spillway tunnels. The spillways can be seen directly above the outer diversion tunnels. They drop sharply from their entrance point and merge directly into the old diversion tunnels.

The two inner diversion tunnels have two concrete plugs in them. One is roughly half way along their length, and the other is around 75% of the way along their length. The section sandwiched between two concrete plugs is used as part of the tunnel which water travels along, to journey from the outermost intake towers and the generators. The two innermost intake towers have separate tunnels.

The large spillway tunnels have only been used three times in the history of the dam. The first one was during the second half of 1941 for testing. The second one was for about six weeks during the summer of 1983, when record precipitation and snow-melt in the Colorado River basin drained into Lake Mead, and the third one in 1999, again with heavy precipitation that filled Lake Mead.

The first concrete was placed into the dam on June 6, 1933. Since no structure of the magnitude of the Hoover Dam had been constructed, many of the procedures used in construction of the dam were untried. Since concrete heats up and contracts as it cures, uneven cooling and contraction of the concrete posed a serious problem. The Bureau of Reclamation engineers calculated that if the dam were built in a single continuous pour, the concrete would have taken 125 years to cool to ambient temperature. The resulting stresses would have caused the dam to crack and crumble. To solve this problem the dam was built in a series of interlocking trapezoidal columns. Each pour was no more than six inches deep. Because of this depth it is extremely unlikely that construction workers were accidentally buried alive in the concrete, contrary to popular folklore. To further cool the concrete each form contained cooling coils of 1 inch (25.4 mm) thin-walled steel pipe. River water was circulated through these pipes to help dissipate the heat from the curing concrete. After this, chilled water from a refrigeration plant on the lower cofferdam was circulated through the coils to further cool the concrete. After each layer had sufficiently cooled the cooling coils were cut off and pressure grouted by pneumatic grout guns. The concrete is still curing and gaining in strength as time goes on. There is enough concrete in the dam to pave a two-lane highway from San Francisco to New York.

Photo by Creativity+ Timothy K Hamilton

There were 112 deaths associated with the construction of the dam. There are different accounts as to how many people died while working on the dam and who was the first and last to die. A popular story holds that the first person to die in the construction of Hoover Dam was J. G. Tierney, a surveyor who drowned while looking for an ideal spot for the dam. Coincidentally, his son, Patrick W. Tierney, was the last man to die working on the dam, 13 years to the day later. 96 of the deaths occurred during construction at the site. However, another surveyor died prior while surveying a potential location for the dam and these statistics do not include other incidental and coincidental (heat stroke, heart failure, etc) deaths during construction.

Photo by by Wolfgang Staudt

Statistics
* Construction period: April 20, 1931 – March 1, 1936
* Construction cost: $49 million ($736 million adjusted for inflation from 1936 to 2008)
* Deaths attributed to construction: 112; 96 of them at the construction site
* Dam height: 726.4 ft (221.4 m), second highest dam in the United States. (Only the Oroville Dam is taller)
* Dam length: 1244 ft (379.2 m)
* Dam thickness: 660 ft (200 m) at its base; 45 ft (15 m) thick at its crest.
* Concrete: 4.36 million yd³ (3.33 million m³)
* Maximum electric power produced by the water turbines: 2.08 gigawatts
* Approximate power output: 4 billion KWh per year (i.e. $200 million at $0.05 per kWh)
* Traffic across the dam: 13,000 to 16,000 people each day, according to the Federal

Highway Administration
* Lake Mead (full pool)
* area: 157,900 acres (639 km²), backing up 110 miles (177 km) behind the dam.
* volume: 28,537,000 acre feet (35.200 km³) at an elevation of 1,221.4 feet (372.3 m) .
* With 8 to 10 million visitors each year, including visitors to Hoover Dam but not all traffic across the dam, the Lake Mead National Recreation Area is the fifth busiest National Park Service area.

Photo by chalkie_colour_circles

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Monticello Dam

Monticello Dam is a dam in Napa County, California, United States.
Monticello Dam was constructed between 1953 and 1957. The dam is a medium concrete-arch dam with a structural height of 304 ft (93 m) and a crest length of 1023 ft (312 m). It contains 326,000 cubic yards (249,000 m³) of concrete.

The dam impounds Putah Creek to form Lake Berryessa, the second-largest lake in California. The capacity of the reservoir is 1.602 million acre-feet (1.98 km³). Water from the reservoir is supplied mostly to the North Bay area of San Francisco.

The Monticello Dam Powerplant was built at the dam in 1983 and has three generators. The electrical power is sent mostly to the North Bay area of San Francisco.

The dam is notable for its classic, uncontrolled spillway with a rate of 48,400 cubic feet per second (1370 m³/s) and a diameter at the lip of 87 feet (22 m).

The Monticello Dam overlook is an increasingly popular place as people begin to learn more about their watershed. Built by the United States Government and Solano County (Napa and Yolo Counties opted out) in the mid 1950's, Monticello Dam is operated by Solano County and the resultant reservoir is managed by the U.S. Bureau of Reclamation. The reservoir has a drainage basin of about 360,000 acres, and at normal annual rainfall, it would take 4.5 years to fill up if outflow, infiltration and surface evaporation were ignored and "zeroed out". However, the winters of 1994-95, 95-96, and 96-97 were wet enough to fill the reservoir completely and spill water down the large "Glory Hole" spillway drain visible just beyond the dam. Named for the Morning Glory flower whose shape it resembles, it draws numerous visitors, and its eerie image is captured in many a photograph.

Photo by johnbullas

The construction of a Monticello Reservoir of this capacity will flood the Berryessa Valley which is now utilized from the growing of orchards, vineyards, grain, alfalfa, corn, and pasture grasses. There is a gross area of about 16,700 acres of good agricultural land in the site for a 1,600,000-acre-foot reservoir, most of which is now in use largely for dry farming. Several hundred acres of this land, however, are now irrigated. The owners of this valley and many of the people in Napa County where it is located oppose the Monticello Dam site because these lands will be inundated and the taxable wealth lost to the county. Although it will be necessary to destroy the productivity of these 10,700 acres of land, the construction of the reservoir will make it possible to furnish water for the irrigation of about 78,000 acres of presently unirrigated lands in Solano County, including 56,500 acres in the presently unorganized district, and for a supplement supply to 5,000 acres of presently irrigated lands, and in addition furnish annually 38,000 acre-feet of water for municipal, military, and industrial uses.

Photo by C & M D

Photo by The LSD Express

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The Three Gorges Dam - Yangzi River

The Yangtze Three Gorges Project (TGP) is the largest hydropower-complex project ever built in the world. On April 3 rd 1992 , “the Resolution to Construct the Three Gorges Project on the Yangtze” was approved at the 5 th plenary session of the 7 th National People's Congress. In 1993, the preparation for the construction commenced, and on December 14 th 1994 , the project construction formally started. On November 8 th 1997 , the River Closure was completed, marking the successful fulfillment of the Phase I construction task. In 1998, the Phase II construction of the TGP started in full swing. After 6 years of arduous work, on June 1 st 2003 , the reservoir of the TGP started to store water, and on June 16 th , the double-lane five-step shiplock of the TGP was put into service, and on July 10 th 2003 , the first unit with 700 MW capacity was connected to the grid and began to generate electricity. So far the goals of the phase II construction have been fully achieved. The TGP, which was drawn the world's attention, began to return favor to the society with its comprehensive benefits.With the genial care and strong support form the CPC Central Committee, State Council and the people of the whole nation, all the TGP constructors bearing the lofty ideal of “Committed to Build TGP for China ” honored the mission with 10 years continuous joint efforts and now the dream of the whole China has come true. At the time of realization of the three major goals for Phase II construction, the compiling of this album aimed at introducing the layout of the TGP construction, recording the history of the TGP construction in the past ten years, and showing the main achievement of Phase I & II construction. As a significant infrastructure for the nation to build a well-off society in an all-round way, the TGP is grand and vigorous, complicated in technology and profound in meaning which can not be fully demonstrated only by about a hundred pictures or so. At present, the TGP is still under construction and all the TGP constructors are striving for the successful realization of the goals set in Phase III construction.

Photo by Ray Devlin

TGP is a multi-objective development project with great benefits in flood control, power generation, and navigation and so on. The project consists of river dam, spillway structures, powerhouse, buildings for navigation, etc, and organized by the scheme officially briefed as “developed in one scale, completed in one time, water-storage by stages, and continuous mgiration”. The dam is concrete gravity dam , with the spillway in the middle, and the power house and non-overflow section at both sides . The axial length of the dam is 2309.47m, the crest height is 185m, and the maximum height of the dam is 181m. With a normal storage level at 175m, the total capacity of the reservoir reaches 39.3 billion m 3 , of which the effective flood control capacity reaches 22.15 billion m 3 .

The total period of TGP construction is 17 years, which can be divided into three phases. Phase I (1993~1997) was designed mainly to do advance work for project construction and excavation of diversion channel with the river close-off as the milestone. Phase II (1998-2003) was mainly designed for construction of spillway and left-bank power house and the ship lock, with the completion of initial water storage, commercial operation of first batch of generators and ship lock open to navigation as several significant milestones of this phase. Phase III (2004-2009) has the main task of construction of right-bank dam and powerhouse, which is symbolized as the commercial operation of all the generator units and completion of the project.

Photo by skootter01

The Three Gorges Project has seen over 1.3 million people re-located, from conditions of poverty to relative levels of comfort. Not all Chinese citizens wanted to move, obviously, but many saw it as a way to escape the desperately poor living conditions they had. Almost entirely new cities had to be built higher up on the steep banks of the resevoir, including new bridges and erosion control. The entire project cost only $30b. This seems like a ludicrously low price given the scale of the project. However, Chinese building practises and environmental controls do not hamper projects the way they do in Europe and USA. Having seen the construction first hand, you have to worry about safety and environmental damage such a project costs. However, China will save huge sums of money - and in fact already has, by eliminating devastating flooding on the Yangzi with the Dam and by selling of the energy created by the hydro plant. The project submerges 13 cities, 140 towns, 1352 villages, 600 factories, and 1200 archeological projects. An engineering marvel, but fundamentally flawed project.

The Yangzi (or Yangtze) is the longest river in China, and the third longest in the world. It stretches from a Tibetan plateau over 6000km to the East China Sea at Shangai. It is navigable by ocean going vessels over thousand miles from the mouth.

Photo by TimS

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