(March 2011) The giant structure located in China has already caused more than 3,400 (so far minor) earthquakes. Scientists are now warning that a much bigger disaster could be looming on the horizon. A survey, published in English by Probe International, helps to explain the numerous landslides and other devastations that have forced 300,00 people to leave their homelands.

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No other large-scale project has triggered so much controversy since its beginnings like Three Gorges Dam in China. Its supporters have traditionally argued that the dam was necessary to improve flood control. It is true that the Yangtze River floods have historically claimed many human lives. In the year 1954 more than 30,000 died, and in 1994 the floods caused 20 billion euros of damage. Other pro-dam arguments were the generation of power and the improvement of conditions for waterway transport. Dam opponents, however, predicted enormous ecological and socio-cultural consequences and early on pinpointed the risk of geological hazards.

With a length of 6,380 kilometres, the Yangtze Kiang is the longest river in China, and the third-longest river in the world. It flows from the Tibetan Highlands through the Red Basin, passes through the Three Gorges and the plains of Yichang, and finally enters into the East China Sea near Shanghai.

The idea to build a barrage downstream of the Three Gorges had existed throughout decades. In the 1980s, when energy shortage turned into a problem, the dam became the flagship project of China’s reform policy. Built between 1993 and 2008, the 150-metre-high and 1,983-meter-long dam banks up the water flow of the Yangtze River for around 600 kilometres. The dam’s hydropower station has a rated generator output of 18,200 MW and is therefore the largest of its kind worldwide.

To build the huge dam, more than eight million people had to be moved to other areas most of them involuntarily. The construction costs were budgeted at 75 billion US dollars (up to 2013).

In addition to the massive ecological damage it causes, the gigantic reservoir of the Three Gorges Dam is now increasingly suspects of being a source of earthquakes. The dam is located in the proximity of a geological fault zone and thus is an area prone to earthquakes.

A recent survey published by seismologists of the state-run China Earthquake Administration (previously the China Seismological Bureau) confirms that “the huge Three Gorges Dam must be regarded as a significant trigger of seismic activities in the reservoir area”. The survey, which was recently published in English language by the research institute Probe International*, underpins Chinese news releases and reports by inhabitants of the Three Gorges Region and helps to explain the numerous landslides and other devastations that have meanwhile forced 300,00 people to leave their homelands.

The survey suggests that between June 2003 (when the Yangtze waters began to be banked up) and December 2009, seismic metering devices in the proximity of the reservoir in the Hubei Province observed as many as 3,429 earthquakes.

“This is a thirty-fold increase compared to the time before the dam was built,” says Patricia Adams, Executive Director of Probe International. “Seismic activities became particularly pronounced when the dam operators abruptly raised or lowered the water level of the reservoir.”

So far, most earthquakes have measured less than 2.9 on the Richter scale and were scientifically classified as “micro-seismic earthquakes”. One earthquake, however, measured 4.1 and occurred when the dam operators tried to raise the water table inside the reservoir to a maximum of 175 metres above sea level. Fan Xiao, senior engineer at the Sichuan Geology and Mineral Bureau, warns that “strong earthquakes are likely to become more frequent at high water level as the many small-damage incidents caused by numerous ‘microquakes’ have made the area sensitive to a much bigger event”.

Scientists have long known that large reservoirs may be the trigger of earthquakes. The cause is a phenomenon called “reservoir-induced seismicity” (RIS). In a report featuring 19 impounded reservoirs in China, which were all affected by RIS, 15 happened to have geological properties similar to those found in the Three Gorges. Interest in the RIS phenomenon further increased when geologists found that the Zipingpu Dam in China’s Sichuan Province was to blame for the deadly earthquake of 2008, during which nearly 90,000 people lost their lives. Since that time, both scientists and the population have been even more concerned about the development in the Three Gorges area. If the dam itself were to break, this would have dramatic implications on millions of people living downstream.

Throughout much time, Chinese authorities used to play down or even ignore public fears and worries. But now a change of mind appears to be taking place. The China State Council just recently acknowledged that taking precautionary measures against geological disasters is one issue in the debate around the Three Gorges Dam which deserves urgent attention.

* The Canadian Energy Probe Research Foundation has been devoted to the issues of sustainability and a fair distribution of resources for thirty years. In carrying out its activities, the Foundation relies on the following divisions: Energy Probe, Probe International, Environment Probe, Urban Renaissance Institute, Environmental Bureau of Investigation, and the Margaret Laurence Fund. For more information visit: http://journal.probeinternational.org