Yang: 【7】Prediction

In the future, in order to maximize the utility of the Three Gorges Dam and cut down on sedimentation from the Jinsha River, upstream of the Yangtze River before reaching Yibin in Sichuan, authorities plan to build a series of dams downstream of Jinsha, including Wudongde Dam, Baihetan Dam, Xiluodu Dam, and Xiangjiaba Dam. The total capacity of those four dams is 38,500 MW, almost double the capacity of the Three Gorges. Xiluodu and Xiangjiaba are under construction, while Baihetan is preparing for construction and Wudongde is seeking government approval. Another eight dams are in the midstream of the Jinsha and eight more upstream of it.

However, except the problem I have talked before will be worse in the future, there is another hidden trouble will bring big disaster—silting. Changjiang have a water storage capacity of 39 km3 and a dead storage capacity of 17 km3. Of the sediment entering the reservoir during the first 20 years after the TGD’s completion in 2009, it is estimated that only 30% will be discharged from the dam, the remaining 70% being retained within the reservoir. This means that sediment discharge at Yichang will be reduced to 30% of its input value. From 2030 to 2060, about 56% of the sediment will be retained, and by 2060 – 2110 the propor- tion of sediment trapped within the reservoir will be reduced to 19%.
     

The Yangtze River (undammed) carries about 680 million tons of silt to the East China Sea every year, making it one of the most heavily silted rivers in the world. It is estimated that each year 0.5 billion tons of silt will be trapped behind the dam, decreasing the effectiveness of the dam to prevent flood control and increasing the height of riverbeds, and the possibility of secondary pollution from the release of harmful chemicals that may be carried with river silt, which is erosion. For the first two decades after TGD completion, there should be extensive erosion, but the erosion accumulation should gradually balance out by 2060. However, for the first 50 years after TGD completion, scholars hypothesize that the Changjiang deltaic area should undergo significant morphologic and environmental change because of local and regional erosion. Critics also claim the river won’t flow fast enough to keep the turbines turning and dam itself will become inoperable after a few years as a result of silting. (Figure2: Landslide along the river)

Also, based on the current design, the TGD project cannot provide enough water from the Yangtze River for Beijing. For Beijing to make use of the reservoir water, it would be necessary to raise the height of the dam, rebuild pump stations, or dig a new canal. This would cost as much as constructing another Three Georges dam.
     

      

According to the data given, it is obvious that a larger scheme would contain a larger active storage for more reserve volume to generate greater hydroelectric power. However, due to the greater storage volume, there will be a greater chance for a large reservoir to be produced. Reservoir areas are well known for landslides. The erosion of the reservoir banks may trigger large-scale landslides.

Reference：

"Giant Chinese Dam May Cause Earth to Move, Alaska Science Forum." Giant Chinese Dam May Cause Earth to Move, Alaska Science Forum. <http://www2.gi.alaska.edu/ScienceForum/ASF14/1465.html>.

Lim, Theodore. "All About the Three Gorges Dam." Sherwood Institute All About the Three Gorges Dam Comments. 

<http://www.sherwoodinstitute.org/all-about-the-three-gorges-dam/>.

Min, Kris. "Three Gorges, Infinite Reasons." <http://darwin.bio.uci.edu/%7Esustain/state/kmin.html.>

Yang: 【6】Three Gorges Dam and Lower Yangtzee Recent Droughts

CNN: Trouble for the Three Gorges Dam

    

Even the dam’s ability to regulate the notoriously changeable flow of the 3,900-mile-long Yangtze, one of China’s two major rivers, has been called into question. Faced with a historic drought 2011's spring, cities downstream of the dam have been unable to accommodate oceangoing vessels that usually visit their ports, and about 400,000 residents of Hubei Province lost access to drinking water this month. Although no link has been proved, critics say the dam has changed regional water tables, contributing to the shortage.

 Jonathan Watts wrote in The Guardian: “The drought in the spring of 2011 had a profound impact on the middle stretches of the Yangtze. This has left 1,392 reservoirs in Hubei with only "dead water." Chinese media reported this month that the Yangtze water levels near Wuhan hit their lowest point since the dam went into operation in 2003. Long stretches have apparently been closed to water traffic after hundreds of boats ran aground in the shallows.” “There have been claims that the Three Gorges plant has exacerbated the problem by holding back water for electricity generation, but operators claim they have alleviated the problem by releasing 400m cubic meters of water from the reservoir. As a result the levels have fallen below 156 meters — the amount needed for optimum power generation.” [Source: Jonathan Watts, The Guardian, May 20, 2011]

 The dam had lowered the water in two nearby lakes. Worsening matters, the drought has pitted China’s need for water and its need for energy; this is the time annually when China’s hydropower usually ramps up. Instead, the government has been releasing water from dams, dropping water levels and weakening its power generation ability. At Three Gorges Dam — the world’s largest hydroelectric plant — the government has increased the water being released, from 7,000 cubic meters per second on May 7 to 11,000 cubic meters recently, drastically dropping the dam’s water levels.

Reference:

"All About the Three Gorges Dam." Sherwood Institute

            <http://www.sherwoodinstitute.org/all-about-the-three-gorges-dam/>.

"ASIANOW - Asiaweek." ASIANOW - Asiaweek

            <http://www-cgi.cnn.com/ASIANOW/asiaweek/96/0719/ed2.html>.

"Chinese Dam Projects Criticized for Their Human Cost." International Rivers <http://www.internationalrivers.org/resources/chinese-dam-projects-criticized-for-their-human-cost-2978>.

"SPECIAL SERIES; China - Three Gorges Dam - Choking on Growth, Part IV." The New York Times. The New York Times, 19 Nov. 2007 <http://www.nytimes.com/interactive/2007/11/19/world/asia/choking_on_growth_4.html>.