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Three Gorges Dam

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Three Gorges Dam
Construction on the Three Gorges Dam began in 1994 to harness the destructive power of the Yangtze River in China and use it to produce a massive amount of hydroelectric energy. It is both the world's largest dam and hydro electrical power plant. The dam stands 607 feet (185 m) high and 7,575 feet (2,309 m) long.[1] When fully completed in 2009, the power plant will consist of 32 generators capable of producing 10 percent of China's electricity consumption.[2]

Still, despite its economic benefits, the project has been the focus of some controversy. As the result of the dam, a massive reservoir will develop, displacing as many as 1.4 million Chinese citizens and destroying hundreds of cultural sites and relics.[3] There are also reports of severe environmental detriments.

The dam and power plant are estimated to cost $25 billion and employ more than 250,000 people for their construction.

Contents

[edit] Construction History

[edit] The Dam Wall

With a history of disastrous floods, the Yangtze River has killed thousands of people and cost billions of dollars in rehabilitation. The Three Gorges Dam project was developed to control flooding resulting in billions of dollars in savings. In fact, the projected cost of $25 billion is still $1 billion less than the rehabilitation costs after a massive flood in August 1998.[4]

The dam was first proposed early in the 20th century by Sun Yat-Sen, but due to political and economic factors the project was not officially begun until 1994. With 40,000 employees' working day and night the project is estimated for completion in 2009.

However, before any construction on the enormous dam could begin, the powerful Yangtze had to be diverted. Adjacent to the dam site workers created a new channel with massive amounts of explosives and groundwork to divert river flow and accommodate river traffic. The resulting rock debris from the new channel was transported and used to create cofferdams surrounding the dam site.

These cofferdam walls, if not secured properly, could have been extremely unstable. If they to collapsed, it would create a tsunami down the Yangtze, destroying thousands of acres of lands and killing thousands. So, to make them secure, after the rock and debris is placed for the cofferdam, they are solidified with bentonite, a liquid clay and cement mix.

The dam site is then drained by pumping out the water between the two cofferdams.

The main dam wall construction began in fall of 1997. With supplies provided by companies around the world the project used some of the biggest and most revolutionary equipment available.[5] Two of the world's largest cranes, MD 2200 Topbelts, began pouring the first levels of concrete. The MD 2200 Topbelt has a 262-foot (80-m) maximum radius, a maximum load of 60 tons, and a pouring capacity of 262 to 758 cubic yards (200 to 600 m3) per hour.[6]

Concrete is poured into sections, which will cool individually and simultaneously. Together, the sections will create a gigantic monolithic dam wall. The giant cranes pour 350 buckets of cement, 20 tons each, every 24 hours. Both women and men operate the large cranes.

At the peak of construction in 2002, small cracks began to form in the wall. After consulting with Robin Charlwood, chairman of the committee on concrete for dams, construction resumed. His inspection discovered only surface cracks resulting from the expanding of cement.

In August 2003, the main wall was complete.

[edit] The Ship Locking and Lift Systems

The importance of the Yangtze River to the local economies is monumental. Were the flow of trade along the river to stop, the result would be disastrous. So, the dam was fitted with a sophisticated locking system that would allow for the continued passing of ships, both large and small.

Water behind the dam had risen 500 feet (152 m), which meant ships had to be raised or lowered depending on which way they were heading. The ships had to pass through five locking chambers, which raised or lowered the water level depending on your direction. Each tank took approximately an hour to fill (300,000 gallons (1.1 million L) of water at 100 gallons (379 L) per second), meaning the whole trip through the dam took about four hours.

To speed up this process there is a new lift system being developed and built simultaneously. In hopes of lifting a 3,000-ton ship up and over the dam, initial construction has begun without the knowledge of how such a lift can operate. It remains in the research and planning stages.

[edit] Power Plant

When the Three Gorges' hydroelectric power plant is fully operational in 2009, it will consist of 32 generators capable of producing 22,500 megawatts. It will be more powerful than 18 nuclear power plants, and will conduct 10 percent of China's electricity usage. The hydroelectric power is conducted by water falling through turbines, causing them to spin, creating power and discharging the water back into the Yangtze River. It is a relatively simple, but expensive process. Each one of the power generators cost approximately $150 million. The generators are 700-megawatt Francis-type turbines manufactured by General Electric in Canada, ABB in Switzerland, Siemens in Germany, and Alstom in France.

[edit] Proposed Benefits

Other than producing a massive amount of hydroelectric power, the dam is designed to control floods and improve navigation along the Yangtze River. With a history of disastrous floods occurring once every decade, on average, proponents of the Three Gorges Dam claim it will reduce the occurrence to once every century. This is estimated to save 15 million people and 3.7 million acres (1.5 million ha) of farmland from the threat of death and devastation.[7]

Also, the increased water level allows larger ships to safely navigate the previously treacherous Yangtze. This will be a great benefit for the Chinese economy.

Early construction on the Three Gorges Dam

[edit] Controversy

[edit] Environment

The Three Gorges Dam is built near a fault line where an earthquake may occur. However, since the 1970s, the dam area has been researched and a "magnitude six earthquake is the maximum predicted in the region."[8] The dam was designed to withstanding an earthquake of magnitude seven.

Another environmental concern is over the movement of sediment along the river. Sediment is essential for replacing soil and replenishing fertility along the river. If not properly controlled, sediment will pile up on the reservoir side of the dam, increasing pressure on fault lines. It will also force farmers to use artificial fertilizers, changing the makeup of their soil.

With the submergence of entire cities, including mines, factories, and waste dumps, the river will also be soaking up new pollutants, which could cause further environmental problems.

There are also a variety of concerns for endangered species in the surrounding areas.

[edit] Relocation

One of the most difficult consequences of constructing the dam and reservoir is the raising of the water level will displace as many as 1.4 million people. Some of these families can date their histories back hundreds, if not thousands, of years from where they live. So, these citizens will not only be losing their home, but their entire culture.

Many of the people destined to be relocated claim to not be receiving the necessary funds to relocate their families safely.

[edit] Destruction of Cultural Sites

When the water of the Yangtze River began to rise, archeologists were busy trying to save every last piece of ancient history before it was completely submerged. More than 1,200 sites were being excavated dating back 4,000 years. Historians raced the water before the ancient relics were lost to the coming tide. In a short time they were able to fill museums with a variety of unique items.

The sinking of history also included many temples along the river. Some were able to be physically moved brick by brick while others were subject to the rising shores.

[edit] Equipment Used

[edit] References

  1. Three Gorges Dam. Answers.com. 2008-09-19. (Columbia Encyclopedia)
  2. China’s Mega Dam, Discovery Channel (DVD)
  3. Three Gorges Dam. Answers.com. 2008-09-19. (Columbia Encyclopedia)
  4. China’s Mega Dam, Discovery Channel (DVD)
  5. Three Gorges Dam. Three Gorges Probe. 2008-09-19.
  6. Three Gorges Dam. Potain. 2008-09-19.
  7. Three Gorges Dam Project. 2008-09-19.
  8. Shaw, Raynor. Three Gorges and the Yangtze River, Chongqing to Wuhan. Pg. 15