For comparison purposes, conjure a mental image of Niagara Falls and the huge hydro plant there that generates 2,300 megawatts of electricity. Multiply by 10, and you'll get a rough idea of the magnitude of China's colossal Three Gorges Dam hydroelectric project, which will generate 26,000 megawatts when complete -- but not before emptying out nine large cities and displacing 2 million people.

The macro is too staggering. We need something micro to grasp it, and Chinese-Canadian director Yung Chang provides it in "Up the Yangtze," a powerful documentary about the Three Gorges Dam's impact on the lives of rich, poor and entrepreneurial Chinese alike.

The dam is actually a macro, micro and mega metaphor for rapidly changing China and, for that matter, the whole brave new globalized world. Chang's focus is on the daughter of a poor family who goes to work on a "farewell cruise" ship catering to American tourists as it travels up the Yangtze, affording views of life along the soon-to-be-submerged countryside.

Talk about culture shock: Sullen 16-year-old Yu Shui finds herself thrown into a corporate culture whose managers immediately give her and her co-workers tourist-friendly English names: Clueless little Yu Shui becomes "Cindy." A cocky 19-year-old boy, Chen Bo Yu, who fancies himself a singer, is rechristened "Jerry."

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'Up the Yangtze'

4 stars = Outstanding
Ratings explained

• Rating: PG in nature for subtitles
• Web site: www.uptheyangtze.com

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Which one of them will make it?

As the dam waters slowly engulf Yu Shui's family hut on the shore, her father and mother keep dragging their humble belongings higher and higher -- to little avail. Meanwhile, Chang takes a wry upstairs/downstairs approach to showing us life on the luxury boat. His amazing "reality-show" footage, beautifully and hypnotically paced, is graced with time-lapse dissolves of the submerging hut and spectacular editing.

This soulful, poetic meditation is most concerned with people: the old evicted farmers, the young people "indentured" to Western tips. A band plays "Yankee Doodle" for the tourists as they board the boat. But the film wisely approaches it all with irony instead of outrage, letting viewers draw their own conclusions.

Sun Yat-sen, by the way, first proposed a hydroelectric plant at the Three Gorges in 1919. Mao revived the idea in the 1950s. Its potential benefits include flood control as well as an enormous amount of clean hydroelectric power. Potential drawbacks, aside from all the human tragedy and misery, include eco-disaster (theYangtze river dolphins are already just about extinct), deforestation, vastly increased pollution and the loss of 1,300 priceless archaeological and cultural sites.

Oh, and one more little thing: The dam sits on a seismic fault.

Hold your breath.

See the movie.

Opens Friday at the Harris Theater, Downtown. In Mandarin and English, with subtitles.