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Of the 3,000 to 4,000 remaining critically endangered Siberian Crane, a large number currently spend the winter in wetlands that will be destroyed by the Three Gorges Dam. The dam also contributed to the functional extinction of the Baiji, the Yangtze river dolphin. In addition, populations of the Yangtze sturgeon are guaranteed to be "negatively affected" by the dam. There are high levels of pollution currently in the Yangtze. Over one billion tons of wastewater are released annually into the river.[52] The dam will significantly decrease the river's flushing capacity and the pollution ratings will increase. For the current amount of pollution, there is an estimated cost of 2.8 billion Yuan to clean the river.
While logging in the area was required for construction which adds to erosion, stopping the periodic and uncontrolled flooding of the river will lessen bank erosion in the long run. The build up of silt in the reservoir will, however, reduce the amount of silt transported by the Yangtze River to the Yangtze Delta and could reduce the effectiveness of the dam for electricity generation and, perhaps more importantly, the lack of silt deposited in the peninsula could result in erosion and sinking of coastal areas.
Effect on local culture and aesthetic values
The 600 kilometer (375 mi) long reservoir has or will flood some 1,300 archaeological sites and alter the appearance of the Three Gorges as the water level rises over one hundred meters at various locations.[53] Cultural and historical relics are being moved to higher ground as they are discovered but the flooding of the Gorge will undoubtedly cover some undiscovered relics. Some other sites cannot be moved because of their location, size or design. For example the hanging coffins site high in the Shen Nong Gorge is inherently part of the sheer cliffs themselves.[54]
These historical sites contain remnants of the homeland of the Ba, an ancient people who settled in the region more than 3000 years ago.[55] One of the traditions of the Ba was to bury the dead in coffins in caves high on the cliff, some of which are submerged and others will soon be submerged.[54]
Sedimentation
There are two hazards uniquely identified with the dam. One is that sedimentation projections are not agreed upon, and the other is that the dam sits on a seismic fault.[56]
The Three Gorges area currently has 10% forestation, down from 20% in the 1950s. At current levels 80% of the land in the area is experiencing erosion causing about 40 million tons of sediment to slide into the Yangtze annually.[57] The relocation of people from the reservoir area will cause further deforestation and erosion due to agricultural needs.
Excessive sedimentation can block the sluice gates which can cause dam failure under some conditions. This was a contributing cause of the Banqiao Dam failure in 1975 that precipitated the failure of 61 other dams and resulted in over 20,000 deaths. Critics believe that the Yangtze will add 530 million tons of silt into the reservoir on average per year; in time, this silt could accumulate behind the walls of the dam, clogging the turbines' entranceway. Further, the absence of silt down stream would have two dramatic effects:
- Some hydrologists think that this could make downstream riverbanks more vulnerable to flooding.[citation needed]
- The city of Shanghai, more than one thousand miles (1600 km) away from the dam, rests on a massive plain of sediment. The "arriving silt -- so long as it does arrive -- strengthens the bed on which Shanghai is built... the less the tonnage of arriving sediment the more vulnerable is this biggest of Chinese cities to inundation..."[58]
Also, the weight of the dam and reservoir can cause induced seismicity, which occurred with the Katse Dam in Lesotho. The Benthic sediment build up is a cause of biological damage and reduction in aquatic biodiversity.[59]
posted on 2008-05-13 10:47
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