Ye Jianchun, China’s vice-minister of water resources, said at a Monday briefing the “detailed scheduling” of water discharges from reservoirs, particularly the Three Gorges, had been effective in controlling floods this year.
He said 64.7 billion cubic metres of floodwater has been stored in 2297 reservoirs, including 2.9 billion cubic metres at Three Gorges.
As many as 33 rivers in China have risen to their highest levels in history during the current wave of floods, Ye said, as regions across the country brace for another “grim” week of torrential rain.
He said 433 rivers – as well as major lakes like the Dongting, the Poyang and the Tai – have all risen beyond their warning levels since the flood season began in June.
“Going into the key flood-prevention period of late July to early August, the current trends remain grim on the Yangtze and the Lake Tai basins,” he said, adding that the belts of heavy rain that have lashed central China would eventually head north.
Average rainfall has been at its highest since records began in 1961. The Emergency Ministry said 141 people were dead or missing as of last Friday, with economic losses at around 60 billion yuan ($12.3 billion).
The company running the Three Gorges Project also said on Saturday that downstream water discharges had been halved since July 6, “effectively reducing the speed and extent of water level rises on the middle and lower reaches of the Yangtze”. The total amount of stored floodwater had reached 88 per cent of the reservoir’s total capacity, it added.
But parts of the Yangtze, its tributaries and the major lakes have hit record levels anyway.
Fan Xiao, a Chinese geologist and long-standing critic of giant dam projects, said the storage capacity at Three Gorges amounts to less than 9 per cent of average floodwater.
“It can only partially and temporarily intercept the upstream floods, and is powerless to help with floods caused by heavy rainfall in the middle and lower reaches of the Yangtze River,” he said.
Fan said Three Gorges and other major dam projects could even make flooding worse by altering the flow of sedimentation down the Yangtze. The project’s need to generate electricity has also undermined flood control, he said.
“When people only consider using reservoirs to solve flood-control problems, they often overlook or even weaken the natural ability of rivers and their lakes to regulate floods,” he said.
Shankman said that the Three Gorges Dam helped alleviate flooding during normal years, but that it was always likely to be vulnerable to more extreme weather, a problem that was exacerbated by shrinking flood plains downstream.
“The Three Gorges Dam reservoir does not have the capacity to significantly affect the most severe floods,” he said.
“Floodwater storage along the middle Yangtze is less because of stronger levees that are less likely to fail,” he added. “Both of those things are at play here. This was predictable.”