The Three Gorges Dam is the world's largest hydroelectric dam, spanning the Yangtze River in Hubei province, China. It became fully functional on 4 July, 2012, and has the capacity to produce 84.7 billion kw of energy annually. Though it has extremely sophisticated engineering, and is hoped to help China reduce its carbon emissions, its construction and effects have been controversial.
The dam is 7,661 feet (2,335 m) long at the top, with a reservoir of about 410 miles (660 km) long and 3,7000 ft (1.12 km) wide. To put that in perspective, it is about five times the size of the Hoover Dam in the US. The project took 21 million cubic yards (16 million cubic meters) of concrete to build, which set a world record. It has 32 main power generators, which can produce 700 MW each, along with two smaller generators that can produce about 50 MW each. The Three Gorges Dam can produce enough energy to power over 20 million households. Its primary functions are to produce energy and to control flooding.
When working at full capacity, the Three Gorges Dam can reduce coal consumption by 31 million tons per year, significantly reducing China's carbon emissions and saving hundreds of thousands of lives affected by disease caused by smoke from coal plants. It also serves an important function for flood control. Every few decades, major flooding of the Yangtze occurs, killing thousands, displacing millions, and doing billions of dollars in property damage. The Three Gorges Dam blocks the waters of the river and causes them to be released in a measured fashion, preventing flooding. Additionally, it allows ships of much greater tonnages to navigate the river, which has greatly increased shipping along the river and improved the transportation of goods into the interior of China.
Despite its benefits, the Three Gorges dam has had negative benefits both environmentally and socially. It has greatly reduced the amount of sediment flowing downstream, which is expected to change the ecosystem and lead to less biodiversity. Its location is problematic as well, since it is located on a seismic fault, leading many scientists to predict that it will cause or exacerbate earthquakes. Many landslides have already taken place since construction began, with almost 24 a month happening in the first four months of 2010. In addition, the dam has had serious effects on the plant and animal life surrounding it, contributing to the endangerment of many species. There are fears that the reservoir will become unusable as it becomes filled with pollutants from upstream.
In terms of social effects, millions of people were relocated, sometimes without compensation, to make room for the dam's construction and reservoir. Estimates range from between around 1.5 million to 4 million people being forced to move since construction started. Those who did receive compensation were often given much less than they needed to start a new home, and those who did not were not given an effective means of filing complaints or seeking help.