Three Gorges Dam reaches full capacity - for an hour

PUBLISHED : Wednesday, 27 October, 2010, 12:00am
UPDATED : Wednesday, 27 October, 2010, 12:00am

It took 17 years for the water level at the Three Gorges Dam to reach full capacity - 175 metres - yesterday.

But while it should have remained there for five months, by design, or at least two months for experimental purposes, the glorious moment lasted less than an hour.

As China Three Gorges Corporation president Cao Guangjing announced at 9am that the 175-metre level had been reached, intake gates were being raised to lower the water level. Data from the corporation's website shows that an hour later the level had dropped by six centimetres. By 3pm it was 174.79 metres.

But in an interview with Xinhua yesterday, Cao did not mention the retreat from maximum level.

'The 175-metre level will run until mid to late December, which is about two months,' the news agency quoted Cao as saying.

He said the deformation of the dam structure fell within the predicted range, seepage was negligible, seismic activities quiet, ship locks normal, power units ran smoothly and the dam gates were secure. In other words, everything was fine.

Some experts said the hasty retreat from full capacity showed that the event was more of a political gesture and the dam was still far from ready to deliver the anti-flooding, power generation and shipping benefits officially promised.

Professor Zhang Boting, deputy secretary general of the China Society for Hydropower Engineering, said that the main purpose of raising the water level to full capacity was to make a statement to sceptics.

One of their biggest arguments about the project was that the dam could not, and should not, operate at the 175-metre level, he said.

Zhang said the authorities had raised the water to that level to prove the sceptics wrong, that the dam could handle the water pressure, no landslide would take place along the banks, and the project's economic, ecological and social benefits could be maximised, as planned.

'Some people, intellectuals and even senior government officials have had doubts about the Three Gorges project,' he said. 'We hope the landmark event yesterday can correct their misunderstanding about the dam.'

But Zhang admitted that the time spent at full capacity was well short of the five months envisioned by the dam's designers. 'In order to reach 175 metres the dam started to store water earlier than usual, so now there is still a risk of flooding,' he said. 'I think the level will drop a metre, stay there for a while and come back.'

But Fan Xiao, chief engineer of the Sichuan Geology and Mineral Bureau, said there might be reasons other than the risk of flooding behind the hasty retreat.

He said the higher water level had threatened some upstream communities of tens of thousands of residents near Chongqing , with a medium-sized shower capable of submerging them, but it had also reduced bridge heights over the Yangtze River, prompting strong complaints from shipping operators.

The risk of geological disasters - from mudslides to earthquakes - might also have been a factor. 'You can see how nervous they are by how fast the water drops,' Fan said.

Yang Yong , another Sichuan-based geologist, said the authorities would have tremendous difficulty maintaining the 175-metre level, an optimal target set in the early 1990s. 'Almost everything has changed in the past two decades,' said Yang, who has been closely monitoring the dam project.

The number of landslides surged, the annual inflow fell and the thriving industries and cities downstream called for much more water than the dam designers expected. But the dam authorities still tried as hard as possible to store water because anything lower than 175 metres would leave power generators idle.

And with large hydropower stations being built upriver there would soon be even less water for the dam's normal operation. 'Soon they will have difficulty maintaining the minimum 155-metre level,' Yang said.