Three Gorges DamEdit profile
The Three Gorges Dam (simplified Chinese: 长江三峡大坝; traditional Chinese: 長江三峽大壩; pinyin: Chángjiāng Sānxiá Dàbà) is a hydroelectric dam that spans the Yangtze River by the town of Sandouping, located in the Yiling District of Yichang, in Hubei province, China. The Three Gorges Dam is the world’s largest power station in terms of installed capacity (20,300 MW) but is second to Itaipu Dam with regards to the generation of electricity annually.
The dam body was completed in 2006. Except for a ship lift, the originally planned components of the project were completed on October 30, 2008, when the 26th turbine in the shore plant began commercial operation. Each turbine has a capacity of 700 MW. Six additional turbines in the underground power plant are not expected to become fully operational until mid-2011. Coupling the dam's thirty-two main turbines with two smaller generators (50 MW each) to power the plant itself, the total electric generating capacity of the dam will eventually reach 22,500 MW.
As well as producing electricity, the dam increases the Yangtze River's shipping capacity, and reduces the potential for floods downstream by providing flood storage space. The Chinese government regards the project as a historic engineering, social and economic success, with the design of state-of-the-art large turbines, and a move toward limiting greenhouse gas emissions. However, the dam flooded archaeological and cultural sites and displaced some 1.3 million people, and is causing significant ecological changes, including an increased risk of landslides. The dam has been a controversial topic both in China and abroad.History
A large dam across the Yangtze River was originally envisioned by Sun Yat-sen in The International Development of China, in 1919. He stated that a dam capable of generating 30 million horsepower (22,371 MW) was possible downstream of the Three Gorges. In 1932, the Nationalist government, led by Chiang Kai-shek, began preliminary work on plans in the Three Gorges. In 1939, Japanese military forces occupied Yichang and surveyed the area. A design, the Otani plan, was completed for the dam in anticipation of a Japanese victory over China. In 1944, the United States Bureau of Reclamation chief design engineer, John L. Savage, surveyed the area and drew up a dam proposal for the 'Yangtze River Project'. Some 54 Chinese engineers went to the U.S. for training. Some exploration, survey, economic study, and design work was done, but the government, in the midst of the Chinese Civil War, halted work in 1947.
After the 1949 Communist victory, Mao Zedong supported the project, but began the Gezhouba Dam project first, and economic problems including the Great Leap Forward and the Cultural Revolution slowed progress. After the 1954 Yangtze River Floods, in 1956, Mao Zedong authored "Swimming", a poem about his fascination with a dam on the Yangtze River. In 1958, after the Hundred Flowers Campaign, some engineers who spoke out against the project were imprisoned.
During the 1980s, the idea of a dam reemerged. The National People's Congress approved the dam in 1992: out of 2,633 delegates, 1,767 voted in favour, 177 voted against, 664 forfeited, and 25 members did not vote. Construction started on December 14, 1994. The dam was expected to be fully operational in 2009, but additional projects such as the underground power plant with six additional generators are expected to delay full operation until mid-2011. The ship lift is expected to be completed in 2014. The dam had raised the water level to 172.5 m (566 ft) above sea level by the end of 2008 and the maximum level of 175 m (574 ft) by October 2010.Layout and scale
Made of concrete, the dam is 2,335 m (7,661 ft) long, and the level of the dam top is 185 metres (607 ft) above sea level. The project used 27,200,000 cubic metres (35,600,000 cu yd) of concrete (mainly for the dam wall), 463,000 tonnes of steel (enough to build 63 Eiffel Towers) and moved about 102,600,000 cubic metres (134,200,000 cu yd) of earth. The concrete dam wall is 181 metres (594 ft) high above the rock basis.
When the water level is at its maximum of 175 metres (574 ft) above sea level (110 metres (361 ft) higher than the river level downstream), the dam reservoir is on average about 660 kilometres (410 mi) in length and 1.12 kilometres (0.70 mi) in width. It contains 39.3 km3 (31,900,000 acre·ft) of water and has a total surface area of 1,045 km². On completion, the reservoir flooded a total area of 632 km² of land, compared to the 1,350 km² of reservoir created by the Itaipu Dam.Economics
The government estimates that the Three Gorges Dam project will cost 180 billion yuan (US$22.5 billion). By the end of 2008, spending had reached 148.365 billion yuan, among which 64.613 billion yuan was spent on construction, 68.557 billion yuan on relocating affected residents, and 15.195 billion yuan on financing. It is estimated that the construction cost will be recovered when the dam has generated 1,000 TWh of electricity, yielding 250 billion yuan. Full cost recovery is expected to occur ten years after the dam starts full operation.
Funding sources include the Three Gorges Dam Construction Fund, profits from the Gezhouba Dam, loans from the China Development Bank, loans from domestic and foreign commercial banks, corporate bonds, and revenue before and after the dam is fully operational. Additional charges were assessed as follows: Every province receiving power from the Three Gorges Dam has to pay ¥7.00 per MWh extra. Other provinces had to pay an additional charge of ¥4.00 per MWh. Tibet pays no surcharge.Power generation and distribution
Power generation is managed by China Yangtze Power a listed subsidiary of China Three Gorges Corporation (CTGC) a Central Enterprise SOE administered by SASAC. The Three Gorges Dam is the world’s largest capacity hydroelectric power station with twenty-nine 700 MW turbines and a total capacity of 20,300 MW. Eventually, it will have 32 generators: 30 main generators, each with a capacity of 700 MW, and two plant power generators, each with capacity of 50 MW, making a total capacity of 22,500 MW. Among those 32 generators, 14 are installed in the north side of the dam, 12 in the south side, and the remaining six in the underground power plant in the mountain south of the dam. The expected annual electricity generation will be over 100 TWh.Generators
The main generators weigh about 6,000 tonnes each and are designed to produce more than 700 MW of power. The designed head of the generator is 80.6 meters (264 ft). The flow rate varies between 600–950 cubic metres per second (21,000–34,000 cu ft/s) depending on the head available. The greater the head, the less water needed to reach full power. Three Gorges uses Francis turbines. Turbine diameter is 9.7/10.4 m (VGS design/Alstom's design) and rotation speed is 75 revolutions per minute. Rated power is 778 MVA, with a maximum of 840 MVA and a power factor of 0.9. The generator produces electrical power at 20 kV. The outer diameter of the generator stator is 21.4/20.9 m. The inner diameter is 18.5/18.8 m. The stator, the biggest of its kind, is 3.1/3 m in height. Bearing load is 5050/5500 tonnes. Average efficiency is over 94%, and reaches 96.5%.
The generators are manufactured by two joint ventures. One of them includes Alstom, ABB Group, Kvaerner, and the Chinese company Haerbin Motor. The other includes Voith, General Electric, Siemens (abbreviated as VGS), and the Chinese company Oriental Motor. The technology transfer agreement was signed together with the contract. Most of the generators are water-cooled. Some newer ones are air-cooled, which are simpler in design and manufacture and are easier to maintain.Generator installation progress
The 14 north side generators are in operation. The first (No. 2) started on July 10, 2003. The north side became completely operational September 7, 2005 with the implementation of generator No. 9. Full power (9,800 MW) was only reached on October 18, 2006 after the water level reached 156 m.
The 12 south side generators are also in operation. No. 22 began operation on June 11, 2007 and No. 15 started up on October 30, 2008. The sixth (No. 17) began operation on December 18, 2007, raising capacity to 14.1 GW, finally surpassing Itaipu (14.0 GW), to become the world's largest hydropower plant by capacity.
Testing on the last six generators in the underground power house began in April 2011 and the first three were operational by June. They are expected to be online by the end of 2011. When operational, the dam will have reached its maximum installed capacity.Output milestones
By September 16, 2009, the plant had generated 348.4 TWh of electricity. Its 18,300 MW installed capacity is about 4,300 MW more than Itaipu but Itaipu produces more TWh of electricity than Three Gorges due to more substantial river flows. In July 2008 it generated 10.3 TWh of electricity, its first month over 10 TWh. On June 30, 2009, after the river flow rate increased to over 24,000 m3, all 28 generators were switched on, producing only 16,100 MW because the head available during flood season is insufficient. During an August 2009 flood, the plant first reached its maximum output for a short period.
During the November to May dry season, power output is limited by the river's flow rate, as seen in the diagrams on the right. When there is enough flow, power output is limited by plant generating capacity. The maximum power-output curves were calculated based on the average flow rate at the dam site, assuming the water level is 175 m and the plant gross efficiency is 90.15%. The actual power output in 2008 was obtained based on the monthly electricity sent to the grid.
The Three Gorges Dam reached its design-maximum reservoir water level of 175 m (574 ft) for the first time on October 26, 2010, in which the intended annual power-generation capacity of 84.7 TWh was realized. The same year, Itaipu generated 85.97 TWh.Distribution
The State Grid Corporation and China Southern Power Grid paid a flat rate of ¥250 per MWh (US$35.7) until July 2, 2008. Since then, the price has varied by province, from ¥228.7–401.8 per MWh. Higher-paying customers receive priority, such as the city of Shanghai. Nine provinces and two cities consume power from the dam.
Power distribution and transmission infrastructure cost about 34.387 billion Yuan. Construction was completed in December 2007, one year ahead of schedule.
Power is distributed over multiple 500 kilovolt (kV) transmission lines. Three Direct current (DC) lines to the East China Grid carry 7,200 MW: Three Gorges – Shanghai (3,000 MW), HVDC Three Gorges – Changzhou (3,000 MW), and HVDC Gezhouba – Shanghai (1,200 MW). The alternating current (AC) lines to the Central China Grid have a total capacity of 12,000 MW. The DC transmission line HVDC Three Gorges – Guangdong to the South China Grid has a capacity of 3,000 MW.
The dam was expected to provide 10% of China's power. However, demand has increased more quickly than planned. Even fully operational, it would support only about 3% of 2006 requirements.Environmental impact
According to the National Development and Reform Commission of China, 366 grams of coal would produce 1 kWh of electricity during 2006. At full power, Three Gorges reduces coal consumption by 31 million tonnes per year, avoiding 100 million tonnes of greenhouse gas emissions, millions of tonnes of dust, one million tonnes of sulfur dioxide, 370,000 tonnes of nitric oxide, 10,000 tonnes of carbon monoxide, and a significant amount of mercury. Hydropower saves the energy needed to mine, wash, and transport the coal from northern China.
From 2003 to 2007, power production equaled that of 84 million tonnes of standard coal, reducing carbon dioxide by 190 million tonnes, sulfur dioxide by 2.29 million tonnes, and nitrogen oxides by 980,000 tonnes.
The dam increased the Yangtze's barge capacity sixfold, reducing carbon dioxide emission by 630,000 tonnes. From 2004 to 2007 a total of 198 million tonnes of goods passed through the ship locks. Compared to using trucking, barges reduced carbon dioxide emission by ten million tonnes and lowered costs by 25%.Erosion and sedimentation
Two hazards are uniquely identified with the dam. One is that sedimentation projections are not agreed upon, and the other is that the dam sits on a seismic fault. At current levels, 80% of the land in the area is experiencing erosion, depositing about 40 million tons of sediment into the Yangtze annually. Because the flow is slower above the dam, much of this sediment will now settle there instead of flowing downstream, and there will be less sediment downstream.
The absence of silt downstream has three effects:
- Some hydrologists expect downstream riverbanks to become more vulnerable to flooding.
- The city of Shanghai, more than 1,000 miles (1,600 km) away, rests on a massive sedimentary plain. The "arriving silt—so long as it does arrive—strengthens the bed on which Shanghai is built... the less the tonnage of arriving sediment the more vulnerable is this biggest of Chinese cities to inundation..."
- Benthic sediment buildup causes biological damage and reduces aquatic biodiversity.
Earthquake-induced peak ground acceleration coupled with the immense weight of the reservoir water might be able to breach the upstream face of the dam. Erosion in the reservoir, induced by rising water, causes frequent major landslides that have led to noticeable disturbance in the reservoir surface, including two incidents in May 2009 when somewhere between 20,000 and 50,000 cubic metres (26,000 and 65,000 cu yd) of material plunged into the flooded Wuxia Gorge of the Wu River. Also, in the first four months of 2010, there were 97 significant landslides.Waste management
The dam catalyzed improved upstream wastewater treatment around the large city of Chongqing and its suburban areas. According to the Ministry of Environmental Protection, as of April 2007 more than 50 new plants could treat 1.84 million tonnes per day, 65% of the total need. About 32 landfills were added, which could handle 7,664.5 tonnes of solid waste every day. Over one billion tons of wastewater are released annually into the river, which was more likely to be swept away before the reservoir was created. This has left the water looking stagnant, polluted and murky.Forest cover
The Three Gorges area currently has 10% forestation, down from 20% in the 1950s.
The FAO’s research suggests that the Asia-Pacific region will, overall, gain about 6,000 square km of forest in 2008. That is quite a turnaround from the 13,000 square km net loss of forest each year in the 1990s. The main reason is China’s huge reforestation effort. This accelerated after terrible floods in 1998 convinced the government that it must restore tree cover, especially in the mighty Yangtze’s basin upstream of the Three Gorges Dam.Floods, agriculture, industry
An important function of the dam is to control flooding, which is a major problem for the seasonal river of the Yangtze. Millions of people live downstream of the dam, with many large, important cities like Wuhan, Nanjing, and Shanghai situated adjacent to the river. Plenty of farm land and China's most important industrial area are built beside the river.
The reservoir's flood storage capacity is 22 cubic kilometres (18,000,000 acre·ft). This capacity will reduce the frequency of major downstream flooding from once every ten years to once every 100 years. The dam is expected to minimize the effect of even a "super" flood.In 1954 the river flooded 193,000 km2 (74,518 sq mi), killing 33,169 people and forcing 18,884,000 people to move. The flood covered Wuhan, a city of eight million people, for over three months, and the Jingguang Railway was out of service for more than 100 days. The 1954 flood carried 50 km3 of water. The dam could only divert the water above Chenglingji, leaving 30 to 40 km3 to be diverted. Also the dam could not protect the large tributaries such as the Xiangjiang, Zishui, Yuanshui, Lishui, Hanjiang, and Ganjiang.
In 1998 a flood in the same area caused billions of dollars in damage; 2,039 km2 (787 sq mi) of farm land were flooded. The flood affected more than 2.3 million people, killing 1,526.
In early August 2009, the largest flood in five years passed through the dam site. The dam limited the water flow to less than 40,000 cubic metres (52,000 cu yd) per second, raising the upstream water level from 145.13 metres on August 1, 2009, to 152.88 on August 8, 2009. 4.27 cubic kilometres of flood water were captured and the river flow was cut by as much as 15,000 cubic metres per second.
The dam discharges its reservoir during the dry season between December and March every year. This increases the flow rate of the river downstream, and provides fresh water for agricultural and industrial usage. It also improves shipping conditions. The water level upstream drops from 175 m to 145 m, preparing for the rainy season. The water also powers the Gezhouba Dam downstream.
Since the filling of the reservoir in 2003, the Three Gorges Dam has supplied an extra 11 cubic kilometres of fresh water to downstream cities and farms during the dry season.
During the 2010 South China floods, in July, inflows at the Three Gorges Dam reached a peak of 70,000 m3/s (2,500,000 cu ft/s), exceeding the peak during the 1998 Yangtze River Floods. The dam's reservoir rose nearly 3 m (9.8 ft) in 24 hours and reduced the outflow to 40,000 m3/s (1,400,000 cu ft/s) in discharges downstream, effectively alleviating serious impacts on the middle and lower river.Navigating the dam
The installation of ship locks is intended to increase river shipping from ten million to 100 million tonnes annually, with transportation costs cut by 30 to 37%. Shipping will become safer, since the gorges are notoriously dangerous to navigate. Ships with much deeper draft will be able to navigate 1,500 miles (2,400 km) upstream from Shanghai all the way to burgeoning inland city of Chongqing in the Sichuan Basin. It is expected that shipping to Chongquing will increase fivefold.
There are two ship locks installed near the dam. Each of them is made up of five stages, with transit time at around four hours. Maximum vessel size is 10,000 tons. The locks are 280 m long, 35 m wide, and 5 m deep (918 x 114 x 16.4 ft). That is 30 m longer than those on the St Lawrence Seaway, but half as deep. Before the dam was constructed, the maximum freight capacity at the Three Gorges site was 18.0 million tonnes per year. From 2004 to 2007, a total of 198 million tonnes of freight passed through the locks. The freight capacity of the river increased six times and the cost of shipping was reduced by 25%. The total capacity of the ship locks is expected to reach 100 million tonnes per year.
These locks are staircase locks, whereby the lock gates serve as both the upper gate and lower gate. Staircase locks are wasteful of water unless (as here) there is a "up" flight and a "down" flight. The gates are the traditional hinged type, which, if damaged, can render the entire flight unusable. Some lock systems (e.g Port of Antwerp) use less vulnerable cylindrical "rotating sector" gates, where each "gate" is a pair of rotating drums. The drums are partially opened to allow water to flow out, thereby obviating the need for sluices and paddles.Ship lifts
In addition to the canal locks, a ship lift, a kind of elevator for vessels, is under construction. The ship lift is designed to be capable of lifting ships of up to 3,000 tons. The original plans specified a lift with the capacity to lift 11,500 ton vessels. The vertical distance traveled will be 113 metres, and the size of the ship lift's basin will be 120x18x3.5 metres. The ship lift, when completed, will take 30 to 40 minutes to transit, as opposed to the three to four hours for stepping through the locks. One complicating factor is that the water level can vary dramatically. The ship lift must work even if water levels vary by 12 meters (39 ft) on the lower side, and 30 metres on the upper side.
The ship lift was not yet complete when the rest of the project was officially opened on May 20, 2006. Construction of the ship lift started in October 2007 and is anticipated to be completed in 2014.Relocation of residents
As of June 2008, China relocated 1.24 million residents (ending with Gaoyang in Hubei Province), about 1.5% of the province's 60.3 million and Chongqing City's 31.44 million population. About 140,000 residents were relocated to other provinces.
Relocation was completed on July 22, 2008. Some 2007 reports claimed that Chongqing City will encourage an additional four million people to move away from the dam to the Chongqing metropolitan area by the year 2020. However, Chongqing City explained that the relocation is due to urbanization, rather than the dam, and people involved including other areas of Chongqing.
Allegedly, funds for relocating 13,000 farmers around Gaoyang disappeared after being sent to the local government, leaving residents without compensation.Other effects
Culture and aesthetics
The 600 kilometers (370 mi) long reservoir flooded some 1,300 archaeological sites and altered the appearance of the Three Gorges as the water level rose over 600 feet (180 m). Cultural and historical relics are being moved to higher ground as they are discovered, but the flooding inevitably covered undiscovered relics. Some sites could not be moved because of their location, size, or design. For example, the hanging coffins site high in the Shen Nong Gorge is part of the cliffs.National security
The United States Department of Defense reported that in Taiwan, “proponents of strikes against the mainland apparently hope that merely presenting credible threats to China’s urban population or high-value targets, such as the Three Gorges Dam, will deter Chinese military coercion.”
The notion that the Taiwanese military would seek to destroy the dam provoked an angry response from the People's Republic of China media. People's Liberation Army General Liu Yuan was quoted in the China Youth Daily saying that the People’s Republic of China would be "seriously on guard against threats from Taiwan independence terrorists."Structural integrity
Days after the first filling of the reservoir, around 80 hairline cracks were observed in the dam's structure. The submerged spillway gates of the dam pose a risk of cavitation, similar to what severely damaged the spillways of the Glen Canyon Dam in the floods of 1983.
The project claimed that 163,000 concrete units of the dam all passed quality testing and that deformation was within design limits. An experts group gave the project overall a good quality rating.Upstream dams
In order to maximize the utility of the Three Gorges Dam and cut down on sedimentation from the Jinsha River, upstream of the Yangtze River before reaching Yibin, China plans to build a series of dams downstream of Jinsha, including Wudongde Dam, Baihetan Dam, Xiluodu Dam, and Xiangjiaba Dam. The total capacity of those four dams is 38,500 MW, almost double the capacity of the Three Gorges. Xiluodu and Xiangjiaba are under construction, while Baihetan is preparing for construction and Wudongde is seeking government approval. Another eight dams are in the midstream of the Jinsha and eight more upstream of it.