The Three Gorges Dam

Flood control and drought relief

The most significant function of the dam is to control flooding, which is a major problem of a seasonal river like the Yangtze. Millions of people live downstream of the dam, and many large and important cities like Wuhan, Nanjing and Shanghai lie next to the river. Plenty of farm land and the most important industrial area of China are built beside the river.

In 1954, the river flooded 47.75 million acres (193,000 km²) of land, killing 33,169 people and forcing 18,884,000 people to move. The flood covered Wuhan, a city with 8 million people, for over three months, and the Jingguang Railway was out of order for more than 100 days.

In 1998, a flood in the same area caused damage to the value of billions of dollars. The Chinese government asked for support from its military to fight the flooding. Two thousand and thirty-nine square kilometers of farm land was flooded. The flood affected more than 2.3 million people, and 1,526 were killed.

The reservoir's flood storage capacity is 22 cubic kilometers (18 million acre feet). This capacity will reduce the frequency of major downstream flooding from once every 10 years to once every 100 years. With the dam, it is expected that major floods can be controlled. If a "super" flood comes, the dam is expected to minimize its effect.

Power distribution

The electricity generated by the Three Gorges Dam project is sold to the State Grid Corporation and China South Power Grid Corporation at a rate of ¥250 per MWh ($32.5 US). Nine provinces and two cities consume the power from it, including Shanghai.

The power distribution and transmission of the Three Gorges Dam project cost about 34.387 billion Yuan. It was completed in December 2007, one year ah...

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...t into the reservoir on average per year, in time, this silt could accumulate behind the walls of the dam, clogging the turbines' entranceway. Further, the absence of silt down stream would have two dramatic effects:

? Some hydrologists think that this could make downstream riverbanks more vulnerable to flooding.[45]

? The city of Shanghai, more than one thousand miles (1600 km) away from the dam, rests on a massive plain of sediment. 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..."

Also, the weight of the dam and reservoir can cause induced seismicity, which occurred with the Katse Dam in Lesotho. The Benthic sediment build up is a cause of biological damage and reduction in aquatic biodiversity.