DAM BREAK IN
CHINA AFTER HEAVY RAIN
COULD POINT
TO A 'BLACK SWAN' DISASTER
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Dam collapse
in China could point to a 'black swan' disaster.
The dam at a
small reservoir in China’s Guangxi region gave way last month after days of
heavy rain in a collapse that could be a harbinger of sterner tests for many of
the country’s 94,000 aging dams as the weather gets more extreme.
Located in
Yangshuo county, famed for its otherworldly karst landscape, the dam collapsed
at around midday on June 7, inundating roads, orchards and fields in Shazixi
village, residents told Reuters.
“I’ve never
seen such flooding,” said villager Luo Qiyuan, 81, who helped build the dam
decades ago.
“The water
levels were never so high in previous years, and the dam had never collapsed.”
Completed in
1965, the dam, made of compacted earth, was designed to hold 195,000 cubic
metres of water, enough to fill 78 Olympic-size swimming pools and meet the
irrigation needs of Shazixi’s farmers.
On a visit
to the reservoir in mid-July, Reuters found the length of the dam, of about 100
metres, had largely vanished. It was reinforced 25 years ago.
The water
went over the dam, which then collapsed, said a member of a survey crew at the
reservoir, declining to be identified as he was not authorised to speak to
media.
Shazixi
residents said there were no deaths.
But the
collapse, which was not reported by domestic media, suggests big storms might
be enough to overwhelm reservoirs, especially if the design is inferior and
maintenance has been patchy.
That raises
the prospect of disaster in river valleys and flood plains that are much more
densely populated than they were when the dams were built.
Environmental
groups say climate change is bringing heavier and more frequent rain. Massive
flooding could trigger unforeseen “black swan” events, the government says,
with extreme consequences.
EXTREME
EVENTS.
Thousands of
dams were built in the 1950s and 1960s in a rush led by Mao Zedong to fend off
drought in a largely agrarian China.
In 2006, the
Ministry of Water Resources said, between 1954 and 2005, dykes had collapsed at
3,486 reservoirs due to sub-standard quality and poor management.
It was
unclear if record-breaking rains were to blame for the Shazixi collapse or if
the dam’s emergency spillway had been blocked by silt or if it was a design
problem.
The water
resources department in the area declined to comment. The county government did
not respond to a request for comment.
In Guangxi,
in southwestern China, rainfall and temperatures were on average significantly
higher in 1990-2018 compared with the previous 29 years, official data shows.
It’s the
extreme events that put dams at risk, said David Shankman, a geographer at the
University of Alabama who studies Chinese floods.
“But a dam
should be able to withstand extreme events even if they become regular, and
when the flood is over, it should be exactly of the same quality as before the
event, if the dam was properly designed and built,” Shankman said.
According to
a notice at the Shazixi reservoir’s monitoring station, the 151.2 metre-tall
dam was built with a once-every-two-century worst-case scenario in mind in
which water was expected to reach 149.48 metres. Last month, it overflowed.
In the
county seat of Yangshuo in June, more rain fell in three hours than usually
falls in two months.
The Ministry
of Water Resources did not respond to a request for comment.
In what
could be another sign of trouble to come, water behind a dam on a tributary of
the Yangtze river rose so sharply that authorities on Sunday were forced to
blow up part of the dam to lower the level.
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