The rising cost of landslides in the Three Gorges dam area

One of the great concerns about the Three Gorges Dam in China has always been the potential for large-scale landslides. As the project nears completion, inevitably very over-budget, the level of the lake is rising and the cost of these landslides in becoming apparent. Today AFP and Xinhua have runs stories that raise concerns still further. These stories report that since September there have been 166 landslide and debris flow events on the banks of the reservoir, forcing the relocation of 28,600 people. The economic losses associated with these slides are approximately US$79 million.

Unfortunately these events have occurred before the onset of this year's rainy season and before the planned further increase in the water level later this year.

Was the Wenchuan (Sichuan) earthquake triggered by humans?

At recent edition of Science carries a really intriguing review piece that examines the triggers of the Wenchuan earthquake. Although earthquake triggering is really beyond the scope of this blog, the huge number of devastating landslides that the earthquake induced means that this is of interest. The article can be read online here.

The article has emerged from work undertaken at two different locations. Christian Klose of Columbia University presented a paper (abstract here) at the AGU Fall meeting in December in which he suggested that the earthquake could have been induced by "local mass imbalances" associated with the accumulation of "at least 320 million tonnes of water" in the upper Min Valley - a clear reference to the construction of the Zipingpu Dam, which is located close to the fault, and which was completed in December 2004. The Google Earth image below shows the dam and lake, although the quality is not great:

The idea is that the additional weight of the water acted in a manner that is very similar to the triggering of landslides on slopes - i.e. it acted to both increase shear stress and to decrease the normal effective stress, rendering the fault more likely to fail (slide). This is apparently backed up by a paper by Lei Xinglin, of the China Earthquake Administration in Beijing and GSK/AIST, which was published in the Chinese journal "Geology and Seismology" last month. That paper is also available online here, but it is in Chinese, so I cannot really tell what it is saying in detail. According to the Science article, the paper apparently also suggests that the reservoir may have been a factor, without coming to a firm conclusion. The diagrams in the paper are worth a look, and have English captions. The abstract is as follows:


So how likely is this? To be honest my gut reaction is not very likely at all, but this certainly needs further work. Klose in his abstract says that:
"Shear stresses increased by >1kPa on the Beichuan fault at the nucleation point in about 20km depth. Normal stresses decreased by <-4kPa and weakened the fault strength. Pore pressure increases might have additionally destabilized the fault locally due to pore pressure diffusion. This effect, however, might be minor in 20km depth, because of low lateral fracture connectivity and permeability between the area of water accumulation and the Beichuan fault."

These stress changes seem to be rather small to have a significant effect. To put this into context, average atmospheric pressure at sea level is 101.325 kPa, so the changes that he is describing are a fraction of this. It is hard to believe that this has had a significant effect at 20 km depth, although the argument seems to be that the fault was so close to rupture that this tipped it over the edge, assisted by pore pressure diffusion. The depth of the earthquake nucleation point also renders this a little dubious, but Klose argues that in fact most of the energy release occurred close to the surface. In addition the fault appears to be rather further from the dam than the article suggests (the Science article says 500 m, but this is surely not the case (I think it is about 30 km to the epicentre for example). Note also that this reservoir is really not very large (c. 8 km long)

It will be very interesting to see how this plays out over the next few months. I remain very doubtful indeed but am certainly open to being persuaded if the science stacks up properly. Of course, if it is the case that the dam was a factor then this would have profound implications legally, socially and in terms of future development, especially given that HEP is coming back into fashion as non-renewable sources of energy decline.

Two interesting recent landslides

Two interesting landslides to report in the last few days.

1. Landslide in Iztapalapa, Mexico City
On Thursday morning a 50 cubic metre landslide in the Itzapalapa, a poor suburb of Mexico City slid onto a house at the toe of the slope, killing two people. Chinagate has published a rather dramatic picture of the site:

The interesting thing about this image is the very large (apparently 5 m high) retaining wall that had been built between the slope and the houses. Clearly the wall has failed under the weight of the landslide (not surprising given the size of those boulders actually), but I wonder who built the wall (surely not the people living in these houses - it is far too big)?

2. Landslide-induced wave on Lake Roosevelt, Washington State, USA
The second is a report from the Spokane arm of Lake Roosevelt near to Spokane in Washington State. The website Spokesman Review is carrying a report that says:

"Property owners in the Spokane arm of Lake Roosevelt were swamped by a huge wave caused by a landslide last Friday. The 17-acre landslide on Jan. 16 near Mill Canyon – northeast of Davenport and downstream from Little Falls Dam – slid into the water, unleashing a wave that reached 30 feet above the full-pool mark across the lake into Breezy Bay, according to Adam Kelsey, chief ranger for the Lake Roosevelt National Recreation Area. Private docks and vessels were destroyed or damaged for at least 1.5 miles downstream from the site."

They also have an image of the site:


It is reasonable to assume that the displaced mass on the far side of the lake is the landslide as the Google Earth image does not show a slide at this site:

It is interesting to note that the section of slope that has failed shows clear signs of toe erosion and some interesting linear features on the Google Earth imagery:

Interestingly, in the years after Lake Roosevelt was filled there were a series of landslides. The Emergency Management Division of Washington Military Department has a document here that describes a series of events as the lake was filled and emptied:

"1944 to 1953 – Massive landslides generated a number of inland tsunamis in Lake Roosevelt in Eastern Washington:
• April 8, 1944 - A four to five million cubic yard landslide from Reed Terrace generated a 30-foot wave, 5,000 feet away on the opposite shore of the lake about 98 miles above Grand Coulee Dam.
• July 27, 1949 - A two to three million cubic yard landslide near the mouth of Hawk Creek created a 65-foot wave that crossed the lake about 35 miles above Grand Coulee Dam; people 20 miles away observed the wave.
• February 23, 1951 – A 100,000 to 200,000 cubic yard landslide just north of Kettle Falls created a wave that picked up logs at the Harter Lumber Company Mill and flung them through the mill 10 feet above lake level.
• April 10 – 13, 1952 – A 15 million cubic yard landslide three miles below the Kettle Falls Bridge created a 65-foot wave that struck the opposite shore of the lake. People observed some waves six miles up the lake.
• October 13, 1952 – A landslide 98 miles upstream of Grand Coulee Dam created a wave that broke tugboats and barges loose from their moorings at the Lafferty Transportation Company six miles away. It also swept logs and other debris over a large area above lake level.
• February 1953 – A series of landslides about 100 miles upstream from Grand Coulee Dam generated a number of waves that crossed the lake and hit the opposite shore 16 feet above lake level. On average, observed waves crossed
the 5,000-foot wide lake in about 90 seconds.
• April – August 1953 – Landslides originating in Reed Terrace caused waves in the lake at least 11 different times. The largest wave to hit the opposite shore was 65 feet high and observed six miles away. Velocity of one of the series of waves was about 45 miles per hour."