Nov 14 (Reuters) - China's Three Gorges Dam lies across the country's longest river, the Yangtze, and will be the world's largest flood control and hydropower station when completed.

Here are some facts about the dam, which scientists have warned is experiencing damaging environmental problems and straining the surrounding land.

LOCATION:

-- The more than a mile-long dam lies on what is regarded as one of the most scenic stretches of the Yangtze River, near Sandouping, in the central province of Hubei.

-- The dam is a third of the way along the river, which winds 6,300 kilometres (3,910 miles) from glacial Tibetan marshlands to the Yellow Sea near Shanghai.

CONSTRUCTION:

-- In 1919, Sun Yat-sen, considered the "father" of modern China, proposed a dam near the Three Gorges. In the 1950s and '60s, the Communist revolutionary leader Mao Zedong encouraged planning for a dam but then abandoned the idea.

-- Construction of the dam began in Dec. 1994, and officials say it will cost $25 billion.

-- Two cities, 11 counties, 116 towns, and hundreds of cultural sites in Hubei province and neighbouring Chongqing municipality have been flooded to create its reservoir. About 1.4 million people have been displaced.

-- State media has said the project could be completed by the end of 2008.

-- The dam is a concrete cavity type, 185 metres high and with a storage capacity of some 39 billion cubic metres of water.

PURPOSE:

-- Flood control, cheap electricity, improved shipping navigation and tourism have all been cited as benefits.

-- At full capacity, the dam should be capable of generating 18,200 megawatts of electricity from 26 power turbines.

-- Ocean-going freighters will be able to sail more safely along the deepened, widened, waterway between the dam and Chongqing, and on to Shanghai, dam builder the China Three Gorges Project Corporation (CTGPC) says.

-- The dam will also tame periodic devastating floods, reducing the Yangtze's major flood threat from once every ten years to once every 100 years, dam officials say.

CONTROVERSY:

-- Environmentalists have long criticised the project, saying that the dam traps silt, causes erosion and has drowned precious natural and cultural treasures. Critics say that the dam's reservoir risks turning into a pool of sewage and industrial chemicals backing onto the mega-city of Chongqing.

-- Many of the people moved to make way for the dam are poor farmers, and in past years there were protests and petitions claiming that the they were victims of inadequate compensation and widespread embezzlement.

Sources: Reuters, China Three Gorges Project (www.ctgpc.com) ((Writing by Gill Murdoch, Singapore Editorial Reference Unit, gill.murdoch@reuters.com, Reuters Messaging gill.murdoch.reuters.com@reuters.net; +65 6870 3922))

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