(August 20, 2012) A severe test of the Three Gorges dam’s capacity to withstand a major flood peak in July initially showed the mighty dam ready and able. However, downstream areas found themselves at higher risk when floodwaters were released by the dam. Meanwhile, upstream areas are threatened when the dam holds floodwaters back. This article looks at the many pressures, and potential disasters, weighing on the ability of China’s biggest dam to fulfill its design mandate and asks: is July’s flood peak just the start?
Floods test Three Gorges Dam
By Deng Quanlun, published by China Dialogue on August 15, 2012
This report is based on an article that first appeared on August 2 in Times Weekly, where Deng Quanlun is a reporter.
Image by Times Weekly
Given the new century has already seen a series of “once-in-a” disasters, perhaps the incredible Three Gorges Dam is only just starting to be tested.
It was the fourth Yangtze flood of the year and, on July 24, the water level at Chaotianmen in Chongqing, western China, hit 187.92 metres – the highest flood peak since 1981. Up to 71,200 cubic metres of water flowed past every second, 28 times faster than the Yellow River and with volumes greater than those recorded during the huge floods of 1998 and 2010. This was the biggest test for the Three Gorges Dam in its nine-year history.
Official reports from Chongqing city indicate its outlying districts of Jiangjin and Yongchuan were badly impacted by the floods. In total, around 163,000 people were affected, including more than 82,000 evacuated from their homes.
Though this was the mammoth dam’s most serious test to date, in terms of what the structure is built to withstand it was a moderate challenge at worst; the kind of thing its operators expect to see every 20 years. After all, the barrage was designed to be able to cope with once-in-a-millennium floods on a daily basis, and to be able to withstand a once-in-10-millennia flood – plus 10%.
Monitoring showed that, when the flood peak reached the dam, displacement, seepage and deformation were all within normal ranges, and all safety indicators remained stable. The dam had already seen three flood peaks earlier that month.
However, as the Three Gorges Dam released more water, the flood risk further down the Yangtze increased. The water level in China’s largest freshwater lake, Poyang, rose to its highest level for two years. Some 2,200 people were assigned to monitor dykes in the lakeside areas of Jiujiang, Shangrao and Nanchang, as well as the stretch of the Yangtze in Jiujiang.
If the rainy season in the upper Yangtze coincides with that of the lower and middle parts of the river, severe flooding can hit the plains downstream. Most years, that doesn’t happen – but this year it did: “That’s the situation we’re seeing now,” said a Yangtze flood-prevention official, “and so there’s a lot of pressure on the lower and middle reaches of the river.”
The Three Gorges project has always been controversial, from early discussions and initial approval to construction and operation. Renowned hydro-engineer Huang Wanli once predicted that the dam would cause Chongqing’s ports to become blocked up with silt and gravel within a decade.
Since the Three Gorges reservoir was filled, there have been no repetitions of the severe flooding of 1998, which killed more than 3,700 people and left 15 million homeless. But the controversy hanging over the dam has spread to questions about its impacts on drought and the downstream climate. These complex issues, which interlink with hot topics like climate change, have sustained the dam as a focus of public debate in China.
In recent years, the Yangtze basin – not usually short of water – has been hit by two serious droughts: first the 2006 summer drought in Sichuan and Chongqing and, more recently, the March 2010 drought, also in the south-west. Some people blamed these disasters on the Three Gorges Dam.
Former chief engineer at Hunan’s water authority Nie Fangrong argues that, though the droughts were caused by a decline in rainfall, they were exacerbated by ecosystem changes wrought in the lower Yangtze River by the Three Gorges dam. But Cao Guangjing, chief executive of dam developer the Three Gorges Group, has pointed out that the structure stores water between August and October every year, and releases increasing amounts of water from January onwards, when the reservoir level drops. During that period, the dam is actually helping to relieve drought, rather than holding water back, he said.
Read the full story on China Dialogue.