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.>