The dam is but the centrepiece of a colossal endeavour to transform the cities of the Yangtze along a 400-mile stretch from the wartime capital of Chongqing, in the west, to the old British treaty port of Yichang, in the east, towards Shanghai and the sea.

The project has cost at least £14 billion, according to figures from Xinhua, the official news agency. Foreign experts put the figure at up to four times higher.

Apart from the enormous human “relocation” to make way for the scheme at least 8,000 archeological sites were submerged for ever in the 400-mile reservoir. So, too, were 1,610 factories now leaching poisons, pollutants and debris into the waters. The drowned factories may be changing the ecology of the river: fishermen have given up their nets in despair and turned to work as coal porters.

As the water inexorably rises over the next few weeks, it will mark the end of 450 years in the same home for the Gong family of Nanling village, near Wushan.

Gong Wanqing, 77, and his 75-year-old wife were trembling with emotion as they surveyed the muddy brown river slipping by the fringe of their fields. “Our new house is ready,” the old man said. “But we just don’t want to go.”

Up the Daning River, a tributary, people were picking their way through the ruins of Dachang, an ancient town reduced to rubble by state edict, and which will vanish beneath the waters this summer.

“We’re getting what we can,” said a sweating coolie, dragging steel cables out of a wrecked concrete building. “Half of us are up there now,” he explained, waving towards the new Dachang — white housing blocks, gleaming in the sunlight, on a clifftop. “The rest have gone all over China.”

Two venerable houses, the clan halls of the Wen family of local notables, stood amid the ruins. One will be dismantled and rebuilt in the new town; the other, victim of an interminable property dispute, awaited its slowly seeping doom.

Down a winding narrow river gorge, Li Xiankai, a villager in the tiny coaling port of Butou, paused, a basket of firewood on his back, to indicate his mudbrick home. His neighbours were energetically helping to dig a road that will go straight through it in the next few days.

“In the old days we had to walk for an hour to the Chang Jiang (Yangtze),” said Li. “Since the water level has risen they can bring boats up to 1,000 tons here to take the coal away. My house is going. I wasn’t happy. But there’s new business and work carrying the coal.”

Soaring coal prices are fuelled by China’s hunger for energy as its economy grows at a pace that is nowhere so visible as in Chongqing, 400 miles west of the dam and the centre of its economic impact.

It is a dizzying scene of construction that looks like an oriental Manhattan, except that its 38 new bridges, sweeping highways and forest of skyscrapers dwarf anything seen in the expansion of 19th-century America.

Halfway from the dam to Chongqing, on the wharf at Wanzhou, stood Liu the pimp, a definite winner, touting his girls at 11.30 on a Wednesday morning to the customers at a pork noodle shop.

“I used to be a farmer down there,” beamed Liu, pointing to the lapping waters. “This is a much better business — I’ve got 15 girls, all nice students, 17 to 18, 250 yuan (£16) for them and 50 yuan for me, at least five customers a night — it’s very busy here now.”

So the “new” China has not entirely washed away the effluent of the old valley of the Yangtze, the guts and soul of a vanished country that went in awe of the emperors, supported the Kuomintang and ameliorated its harshness with poetry, wine and pleasure-boating along the Three Gorges.

Nonetheless, it is a decisive political victory for the Communist party. And on the waterfront at Yichang, once a sleepy port where the gunboats of the Royal Navy’s China station flew the white ensign, banners proclaim the city’s expansion from 100,000 to 1.4m people in just 15 years. It is, they say, “the hydroelectric capital of China”.