15 November 2009

Filling at the Three Gorges Dam suspended due to landslides?

Posted by Dave Petley

Probe International image of a landslide

The Three Gorges Dam in China is one of mankind’s greatest achievements or a folly on a grand scale, depending upon your point of view. Whichever is correct, there is little doubt that its construction is an extraordinary engineering achievement. The final aim of the project was due to be achieved this month as the lake is finally elevated to its maximum level. However, filling of the reservoir has suddenly been suspended four metres short of the maximum level, and there is a great deal of speculation as to why this should be the case.

AP is reporting upon an interesting difference between the official story and that being reported locally. The official story is that filling has had to be suspended due to low river flows caused by a drought downstream in Hunan and Jiangxi, downstream of the dam. However, the AP article speculates that at least in part this cessation of filling may be associated with increasing concerns about the threat of landslides on the gorge walls as the final phase of filling is completed.

So, what is the real situation? Well, there is little doubt that there is a serious drought in southern China at the moment. For example, the China Meteorological Agency reported on 30th October:

“China’s Hunan and Jiangxi provinces, known for their rivers and lakes, are often portrayed as lands abundant with rice and fish. However, even they have not been spared by a drought that has plagued a wide swathe of south and east China since August, usually part of the rainy season. The drought has damaged crops and left 2 million people suffering water shortages and thousands of boats grounded on the shallow rivers or cracked riverbeds...Hunan received 60 percent less rain than normal in August and September. Jiangxi received 60 percent less in September and 90 percent in October.The drought was worsened by unusually high temperatures. The average temperature in Jiangxi was 2.5 degrees Celsius higher than average, and the highest since 1963. The Xiangjiang and Ganjiang rivers, two major tributaries of the Yangtze River running through the provinces, are reporting record low water levels. The water flow in the Xiangjiang River is down to about 500 cubic meters per second, compared to 1,200 cubic meters per second, which is the average for the time of year.”

However, on 6th November the Three Gorges authority reportedly defended the continuing plan to fill the reservoir:
“China Three Gorges Corporation defended the ongoing plan to raise water level in reservoir to 175 meters during dry season, saying its water storage will help prepare for possible worse drought in coming months…Beginning Sunday morning, the Three Gorges project had increased its water flow to downstream to over 9,000 cubic meters per second, about 38 percent more than originally planned, to relieve the drought situation downstream…Demands for the Three Gorges Dam to discharge more reservoir water were on the increase, forcing the project to slow down its water-raising pace to 175 meters, a target that was rescheduled to early November from the end of October. The water level of the Three Gorges reservoir stood at 170.47 meters at around 11:00 a.m. Sunday. Zheng Shouren, Chief Engineer of the Yangtze River Water Resources Committee, said those blaming the drought in Hunan and Jiangxi solely on the Three Gorges project got a partial picture.”

So how likely is it that landslides are the issue? Well, slope instability on the banks of the Three Gorges reservoir has long been a fear (see for example this article from 1999), and there have been many well-documented landslides already. Back in 2007 I wrote an article in China Dialogue expressing concerns about the potential for landslides on the banks of the lake. The concern has certainly increased in recent months, and last week the Chinese investigative magazine Caijing quoted official reports that stated concerns about the likelihood of landslides. AP reports that on 16th October new instability was noted above the township of Quchi, with a tension crack 400 m long being observed.

It is unsurprising that increased movement will be observed as the reservoir rises, although of course as this is the dry season the slopes should be more stable now than they will be in the late summer. However, concerns about instability are of course well-founded, so it will be interesting to watch this story develop.