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The fear is that if the Three Gorges Dam collapses, we're talking 510 million people upstream and downstream of the dam under threat. That's nearly 1/3 of the population of China.

RE: The fear is that if the Three Gorges Dam collapses, we’re talking 510 million people upstream and downstream of the dam under threat.

I dunno, we keep getting regular press releases from the Chinese government telling us not to worry as the Three Gorges Dam will hold.

This is the biggest story in the world right now. You can tell because the US media is putting it in a two-line article on page 35.

A half-billion people, and 50+ nuclear power plants.

Fukushima II, III, IV … LV.

Dam will hold! Yankee propaganda no work! Chinese engineering better!!

[The fear is that if the Three Gorges Dam collapses, we’re talking 510 million people upstream and downstream of the dam under threat. That’s nearly 1/3 of the population of China. ]

But the distances are massive. When the Ruhr and Eder valley dams featured in the Dam Busters movie were damaged, only 1,600 civilians were killed, and the distances were far shorter, with the extreme end of the resulting flood estimated at 50 miles from the dams. The distance from the Three Gorges dams to Wuhan, the first major city that might be affected, is ~200 miles. An excerpt:

https://en.wikipedia.org/wiki/Operation_Chastise#Bomb_damage_assessment
[The two direct mine hits on the Möhnesee dam resulted in a breach around 250 feet (76 metres) wide and 292 feet (89 metres) deep. The destroyed dam poured around 330 million tons of water into the western Ruhr region. A torrent of water around 32.5 feet (10 metres) high and travelling at around 15 mph (24 km/h) swept through the valleys of the Möhne and Ruhr rivers. A few mines were flooded; 11 small factories and 92 houses were destroyed and 114 factories and 971 houses were damaged. The floods washed away about 25 roads, railways and bridges as the flood waters spread for around 50 miles (80 km) from the source. Estimates show that before 15 May 1943 steel production on the Ruhr was 1 million tonnes; this dropped to a quarter of that level after the raid.

The Eder drains towards the east into the Fulda which runs into the Weser to the North Sea. The main purpose of the Edersee was then, as it is now, to act as a reservoir to keep the Weser and the Mittellandkanal navigable during the summer months. The wave from the breach was not strong enough to result in significant damage by the time it hit Kassel (approx. 35 km downstream).

The greatest impact on the Ruhr armaments production was the loss of hydroelectric power. Two power stations (producing 5,100 kilowatts) associated with the dam were destroyed and seven others were damaged. This resulted in a loss of electrical power in the factories and many households in the region for two weeks. In May 1943 coal production dropped by 400,000 tons which German sources attribute to the effects of the raid.[26]

According to an article by German historian Ralf Blank,[27] at least 1,650 people were killed: around 70 of these were in the Eder Valley, and at least 1,579 bodies were found along the Möhne and Ruhr rivers, with hundreds missing. 1,026 of the bodies found downriver of the Möhne Dam were foreign prisoners of war and forced labourers in different camps, mainly from the Soviet Union. Worst hit was the city of Neheim (now part of Neheim-Hüsten) at the confluence of the Möhne and Ruhr rivers, where over 800 people perished, among them at least 493 female forced labourers from the Soviet Union. (Some non-German sources erroneously cite an earlier total of 749 for all foreigners in all camps in the Möhne and Ruhr valleys as the casualty count at a camp just below the Eder Dam.[23]) ]

Having said that, though, the sheer scale of the Three Gorges dam is staggering. The volume of water its reservoir contains is 300x that of the the Dam Busters dams:

https://en.wikipedia.org/wiki/Three_Gorges_Dam
https://en.wikipedia.org/wiki/M%C3%B6hne_Reservoir

While the Chinese dam might seem like a monstrosity, its reservoir capacity is only slightly bigger than either Lake Powell or Lake Mead, the two artificial lakes formed by two of the biggest dams stateside.

https://en.wikipedia.org/wiki/Lake_Powell
https://en.wikipedia.org/wiki/Lake_Mead

Of course, Lake Powell or Lake Mead are only about half full, whereas the water level at the Three Gorges Dam is at the brim, to the point they are doing controlled releases. And the American dams pen in river water that passes through literal deserts while moving downstream. Whereas the areas through which the Yangtze River passes may not have enough water, but they aren’t deserts. The high Yangtze adjacent water table means that dam breaks from the Three Gorges can’t just soak into the parched desert soil the way a Hoover Dam break would eventually do.