Severe rainstorms and flood coming from upstream have put the Three Gorges Dam to the test. Photo: Xinhua

China’s Three Gorges Dam is being put to more and sterner tests as torrential rain pounds provinces along the upper reaches of the Yangtze River, with all its major tributaries already in spate.

During the past weekend, Yangtze’s second flood this year struck the world’s largest hydroelectricity dam spanning Asia’s longest river, with peak flow of more than 60,000 cubic meters per second.

Latest operation statistics about the dam from the official website of the state-owned Three Gorges Group, the dam’s operator, show the mass flow rate at the western approaches of the dam’s reservoir halved to 30,000 cubic meters per second late on Monday.

While the flood was passing, the dam held an aggregate 10.7 billion cubic meters of water, saving the sprawling cities and massive croplands downstream from being submerged, the operator said.

But some experts are not convinced. Fan Xiao, chief engineer with Sichuan’s Provincial Bureau of Geology and Mineral Resources who also writes a column in the Chinese National Geographic magazine, said that based on his back-of-an-envelope calculations, the dam had only held 9% of this year’s Yangtze floods. 

“The dam can only temporarily intercept flooding upstream, but it can do nothing to the flooding from heavy rains in the middle and lower reaches of the Yangtze.”

Fan has gone so far as to suggest that the dam and other huge cement barriers being built and planned to span and harness the Yangtze may exacerbate flooding by altering sediment flows in its lower reaches.

He also said the dam was designed with “once-every-two-century worst-case flooding” in mind, yet it had already failed to perform its flood regulation role even though the current deluge was far less severe than its worst-case design parameters.

Now, after a short respite following the weekend flood, more rainwater has again been flowing in torrents from upstream since Tuesday.

The Chinese Ministry of Water Resources’ Yangtze River Hydrology Committee and China Three Gorges Group noted that to prevent the dam from overflowing, they had lifted more floodgates to drain water at 37,000 cubic meters per second since Tuesday, after the reservoir’s water level increased by more than eight meters in 48 hours to 163.5 meters. The height of the dam is 185 meters.  

The Three Gorges Dam is 185 meters high. Water surging beyond that point may cause its collapse.
Water is discharged from the dam. Photo: Handout

While it is safe to predict that the gigantic steel and concrete barrier on the Yangtze in the central Hubei province is far from riding out the summer rainy season that has drenched almost all southern provinces, Chinese state media has nonetheless since this week toned down its coverage of the dam and the flooding that is still sweeping the region.

Still, there has been no evidence the dam is in any imminent danger of caving in to the pressure of the surging water in its 39.3 billion-cubic-meter reservoir, when the third wave of flooding comes. But that has failed to ensure peace of mind for the 10 million-plus people in the megacity of Wuhan, 250 kilometers east of the dam, who are already bracing for the fresh calamities the flood may cause, merely a few months after the city recovered from the coronavirus scourge.

All of Wuhan, provincial capital of Hubei, and its environs would be the first to be inundated in the unlikely scenario of a devastating dam burst. It is believed, however, that in the contingency plans prepared by the Chinese State Council for such an incident, areas in the immediate proximity of the dam including the seat of Yichang, the prefecture-level city where the dam is situated, will be “sacrificed” as a buffer to mitigate any impact. The full text of the plan is classified as it contains sensitive design parameters of the dam.

When the weekend flood passed the dam and reached Wuhan on Tuesday, water in the Wuhan section of the Yangtze had already surged above the city’s ground level, making it a veritable hanging river.

Wuhan’s average elevation ranges from 21 to 27 meters above sea level while the stormwater runoff has pushed the watermark at a downtown hydrological monitoring station to 28.8 meters on Tuesday, when parts of Wuhan’s Wuchang and Hankou districts were already flooded. 

A riverside pavilion on the bank of the Yangtze in Wuhan is submerged. Photos: China News Service

Currently Wuhan counts on the embankments and dykes along the Yangtze to stay dry but videos about water seeping through a causeway have gone viral on social media platforms. It is said that if the vital line of defense against the deluge collapses, many buildings, especially those in the city’s low-lying areas, will be submerged to three to four storeys.

A postgraduate student at the Wuhan University told Asia Times that other than property losses, residents in the city still reeling from Covid-19 fear more about the health risks after flooding.

“There will always be some sort of epidemic after a city is submerged, so people are sacred, especially after the operator of the Three Gorges Dam started to discharge more water and said cities downstream must not rely on the dam to fend off the flood,” said the civil engineering student.

That said, people in other urban centers in Yangtze’s upper reaches including Chongqing have already attributed the severe waterlogging in their cities throughout previous weeks to the high water levels in the dam’s reservoir, as excessive water must not be drained into the Yangtze for the sake of downstream cities like Wuhan. 

The dam can do almost nothing to mitigate flooding in the lower reaches of the Yangtze. Photo: Xinhua

It has been apparent that Beijing’s overarching goal is to ensure the safety of major cities while smaller counties, villages and croplands can be used as floodwater discharge and diversion areas, provided that evacuation of people can be executed promptly before these places are swamped. 

An official with Anhui’s Water Resources Department also said that water levels along major Yangtze tributaries in the agrarian province had long risen beyond alert levels, according to the readings from the river stage gauges installed there.

“We are not merely issuing warnings for people to stay alert, we are now asking people to seek shelter on high grounds,” said the official who declined to be named.

“To put it simply, an alert level means the water is probably at your waist height but now the situation in Anhui is like it has reached your neck.”

On Saturday, water behind a dam on a Yangtze tributary in the eastern Jiangxi province rose so sharply that authorities scrambled to dispatch military police to evacuate people, before blowing up part of the dam to prevent an uncontrolled collapse that could lead to more severe damage.  

Read more:

Three Gorges Dam deformed but safe, say operators

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