|Fig. 1: Three Gorges Dam (TGD) viewing from north shore, with spillway in the middle and hydroelectric generators on both sides. (Source: Wikimedia Commons)|
The Three Gorges Dam (TGD), across the Yangtze River in China, is the world's largest hydroelectric dam, with a length of 2.3 km and a height of 185 m maximum (Fig. 1).  It is located in the city of Yichang, Hubei province in mid-south China (Fig. 2). The dam body was completed in 2006 and reached a full generating capacity of 18.2 GW in 2010.  Though there have been debates on whether this dam should be built ever since its plan was proposed, the electric power generated and the ability to control floods on Yangtze River gained by the project have indeed brought great benefits to China.
|Fig. 2: Location of TGD, showing major cities along the Yangtze River in China. (Source: Wikimedia Commons)|
The Three Gorges Reservoir Area (TGRA) in the middle part of Yangtze River is one of most famous tourist resorts in China. Besides beautiful cliffs along the shore, Yangtze River itself has plenty of water power resources and causes floods almost every other year. The Three Gorges Dam and Hydroelectric Plant plan was proposed to make use of the water power and control the floods ever since mid-1940s when the US Bureau of Reclamation cooperated with the Chinese nationalist government on potential hydroelectric plants on the Yangtze. The Yangtze Valley Planning Office proposed the dam in the early 1950s and the plan was approved at higher levels in 1958. The tremendous cost of the dam has prevented it from being included in the Five-Year-Plans of China and from actually being constructed. The Chinese government finally decided to launch "TGD 617" project in 1986 despite major unresolved details. In the same year, a "feasibility" study was started, with financing from the Canadian International Development Agency (CIDA). Fourteen Chinese agencies are were studying specific aspects of the proposal, in order to improve the project's design and to reduce its impacts - not to serve as inputs to the decision on whether to build the dam.  Construction of the dam body was started on December 1994 while preparations began in 1993.
|1.||1993-1997:||Yangtze River was diverted after four years' construction on November 1997.|
First batch generators in the north side began generating power in 2003. Temporary ship lock was opened on May 1998. Permanent ship lock for small ships was opened on July 2003.
The last section of dam wall was completed in May 2006. On June 2006, the temporary construction barriers behind the dam were removed. Reservoirs began to fill. The 14 capacity of 9.8 GW on October 2006. The entire project was completed in 2009, when all 26 generators would be able to generate 84.7TWh of electricity annually .
|Fig. 3: Diagram of TGD, showing hydroelectric generators and ship locks.|
With 14 generators in the north side of the dam and 12 in the south side, 700MW each (Fig. 3), the designed full generating capacity of TGD is 18.2 GW, which was already reached on July 2010 during the flood season of Yangtze River.  There are still 6 underground generators currently being built, which will increase the total capacity to 22.4 GW. 
The dam is now managed by China Three Gorges Corporation, a government-owned company. Electric power generated by TGD is sold to nine provinces and two cities including Shanghai, through several AC and DC transmission lines. 
One of the beneficial environmental impacts of TGD is the coal it saves by providing clean hydroelectricity. 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, TGD reduces coal consumption by 31 million tons per year, avoiding 100 million tons of greenhouse gas emissions, millions of tons of dust and other hazardous chemicals.  It also saves the energy and cost needed to transport coal from northern China like Shanxi province to southern China.
|Fig. 4: Satellite map showing areas flooded by the Three Gorges reservoir. (Source: Wikimedia Commons).|
However, with a water level increase of about 175 meters in the TGRA after the completion of TGD, the biodiversity and ecosystem properties in the TGRA are being significantly affected. The TGD influences the ecological processes in the area through both the immediate loss of habitat area and increased isolation of remaining habitat patches. For example, food-web structure and nutrient cycles will be significantly changed on fragmented islands which might result in emerging features of reduced species diversity ; fishes and aquatic mammals that need to swim upstream to breed cannot cross the dam and thus will experience a tremendous decrease in number or even become functionally extinct like Baiji (river dolphin).  In short, the biodiversity and ecosystem functioning of the whole area will have to continue the adaptation to the newly created geological and ecological configuration for decades or even centuries. 
Moreover, though the TGD is doing well in controlling floods of Yangtze River so far, it has posed possible geological hazard to the area. The impoundment of 39.3 billion cubic meters of water has destabilized slopes, heightening risk in a landslide-prone region, while the sheer weight of all that water has heaped strain on seismic faults.  Some researchers even believe that there is probably a connection between large dams on Yangtze River and the great earthquake happened in Sichuan province of China in 2008, killing some 80,000 people. 
The social impact of the dam is also controversial. On the one hand, flood control has helped downstream communities become more prosperous and the increase in water level has made water transport upstream Yangtze River more convenient; On the other hand, The rising waters have also uprooted more than 1 million people and submerged entire communities. Another 4 million of the 16 million people living in the reservoir area may have to be relocated in coming years.  At the same time, many famous attractions along the shores of TGRA, some of which were mentioned even in literary works thousands of years ago, were submerged under water after TGD was built. (Fig. 4) This kind of cultural loss could hardly be estimated by money and was irreversible.
© Yue Ma. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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