Three Gorges Dam, Ecological Concerns
May 26th 2006 02:07
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Sedimentation:
During the construction lifetime of the Three Gorges Project the construction plan has been significantly altered. Originally, the dam was to be constructed to be filled to a height of 156 metres above sea level in 2007 and raised to a final level of 175 metres in 2013. Later, these project milestones were hastened. It was planned to raise the dam to the interim level by 2006 (which was recently achieved) and then raise the dam to its final level by 2009. The economic benefits of raising the dam ahead of schedule are huge. However, the build up of silt in the reservoir will also occur quicker than as originally planned. Computerised sedimentation-modeling experiments predict that silt accumulation in the reservoir would pose a threat to the port of Chongqing after the dam had been in operation for 20 years. With this forecast the region has started the development of a new port 40 kilometres downstream of Chongqing at an estimated cost of US$175. The exact slope of the Three Gorges reservoir makes sedimentation projections difficult. If there is a slope at the tail end of the reservoir near Chongqing, more land will be flooded and more people will have to be relocated than planned. On the other hand, if there is no slope at all to the reservoir, the buildup of silt will be more serious than forecast. The exact slope of the reservoir has been the subject of much debate, with no consensus reached so far.
Landslides:
The Three Gorges region is a densely populated area. In fact, the Three Gorges reservoir area is so crowded that finding the space nearby to for people to relocated who have been displaced by the dam has been hard. This means that even a moderate geological disaster in the reservoir area can entail enormous human and property losses on a personal, regional and national level. In a rural environment landslides caused by the reservoir would not be a significant concern, however, in the highly populated regions of the Yangtze, landslides could be devastating and there are indications that the dam could contribute to a greater risk of landslides upstream of the dam.
“On the morning of July 12, 2003, just one month after the filling of the reservoir, cracks were discovered in the old Qianjiangping landslide. By evening, cracks had also appeared on the walls of a factory building and were growing rapidly. Most of the factory workers and villagers fled as the dangerous situation developed, though a few remained behind. Several hours later and a huge block of the mountain, 24 million cubic metres in volume, slid into the Qinggan River, completely blocking the 100-metre-wide river. The landslide's crash into the river also created 20-metre-high waves that capsized 22 boats. Within a matter of moments, four factories, 300 homes and over 67 hectares of farmland were destroyed.”
- Chinese National Geographic. May 3, 2006
The lost of human life was relatively low due to the early warning and evacuation, but the economical impact was large and in the time scale of the event, difficult to minimize.
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