Watch the dam

Since early June, central China has suffered its worst flooding since at least 1998.  So far, 28,000 houses have been destroyed, 744,000 people have been displaced, and the official death toll is at 141 -- and that's what is admitted by a regime which is still claiming its death toll from covid-19 was less than 4,000.  There have been massive landslides, presumably caused by waterlogged soil, and in one case authorities blew up a dam to relieve the accumulation of water above it.

The worst flooding has been along the Yangtze, China's largest river, whose valley and delta contain a third of the country's population and account for a comparable fraction of its economic output.  Flooding in Wuhan, the main city in the middle part of the Yangtze, has impacted China's exports of medical protective supplies to the US, since much production is centered in the Wuhan area.

Increased rainfall linked to global warming probably plays a role, but this is not the first time China has suffered severe floods (the worst in its modern history, in 1931, killed hundreds of thousands of people -- perhaps millions, when deaths from consequent starvation and disease are added in).  Things were not supposed to be this bad in the 21st century, because of the Three Gorges Dam.

This colossal structure stretches across the Yangtze a few hundred miles above Wuhan.  It is the largest dam in the world, one and a half miles long and over 600 feet high.  The reservoir behind it is over 400 miles long and contains almost ten cubic miles of water.  Finished in 2006, it was built to generate hydroelectric power (installed capacity 22.5 gigawatts) and for flood control.  But this year's flooding has threatened to overwhelm even such a mighty structure's capacity to regulate the flow of water.

As the reservoir's waters rise, authorities have been forced to release some water to relieve pressure on the dam and alleviate flooding in Chongqing and other cities above it.  But doing so worsens the floods in the middle Yangtze, including Wuhan.  So the damage is not being prevented, merely rearranged.  To be sure, controlled releases of water do far less harm than the wild floods which regularly plagued the Yangtze before the dam was built.  But there's another problem.

Anyone familiar with China knows that the country's standards of construction and maintenance are crap (local but telling examples here).  This is due partly to cultural factors and partly to the corruption endemic to authoritarian states.  It's impossible to know to what extent these problems infect a major prestige project like the Three Gorges Dam.  Certainly nothing the regime says can be trusted, any more than its economic statistics, covid-19 figures, etc. can be.  But the rising water pressure behind the dam is subjecting it to structural strain beyond anything it has had to resist since being built -- and in late July and early August the rain is expected to get worse.  If I were living downstream from the damn thing, I'd move.

(In 2019 it was claimed that satellite imagery showed a slight warping of the dam, but this appears to have been due to distortions introduced by image processing.)

How bad would it be if the dam collapsed, as many lesser dams have done during floods in China in the past?  Long-time readers may recall this post from 2008 in which I speculated on that question.  In fact, no one knows what would happen.  The deluge unleashed by the sudden rupture of a reservoir that size would be unlike anything in recorded history, and the region below the dam is among the most densely-populated on Earth.  Various efforts have been made to model the effects, but we don't really know.

It's probable that abnormally-rainy summers like this will become more frequent in future years, due to the effects of global warming.  Each such season will inflict more structural strain on the dam, likely weakening it year by year.  If it finally breaks, there won't be much warning -- and with tens or even hundreds of millions of people under threat, evacuation would be impractical in any case.  China's biggest engineering project since the Great Wall may yet prove one of the biggest mistakes in its history.