Dams and Impounded Rivers - River Dynamics and Integrated River Management - page 434

7.4.1 Construction of the Three Gorges Dam
7.4.1.1 Purposes of the Project
The Yangtze River is the largest and longest river in China, with a drainage area of 1.80 million km 2 . The
Yangtze River basin has an elevation varying from 5,000 m to 0 m with latitude from N25° to N35°. The
river flows through the Qinghai-Tibet Plateau, Yunnan-Guizhou Plateau, Sichuan Basin, Three Gorges,
Jiang-Han Plain, Lower Yangtze Plain, and pours into the East China Sea at Shanghai. From the source
to Yichang (Three Gorges Dam site) is the upper reach, from Yichang to Hukou (Poyang Lake mouth) is
the middle reach, from Hukou to Datong is the lower reach, and below Datong is the estuary.
In China, the Yangtze River is called Changjang (long river), with special names for different stretches:
the lower reaches are called the Yangtze River, the middle reaches are called the Jingjiang River, the reach
from Yichang to Yibin is called the Chuanjiang River, from Yibin to Zhimenda is called the Jinsha River,
and from Zhimenda to the origin is called the Tongtian River (Heaven River). The river has become the
most frequently flooding river in China since the 1950s, before which the Yellow River was the most
disastrous river in China. The Jiang-Han plain is the most flood threatened area, because it is 10-15 m
lower than the flood stage.
The Three Gorges Dam is constructed at Yichang, immediately upstream of the middle reaches of the
river, allowing it to control floods from the upper reaches of the river. The Three Gorges Reservoir is a
river type reservoir, as shown in Fig. 7.32.
Fig. 7.32 Locations of the Three Gorges Dam and the Three Gorges Project reservoir
1) Flood Defense
The most important purpose of the project is to mitigate flood disasters. Historical records show that during
the 2,000 years from the Han Dynasty (206 BC-220) to the late years of the Qing Dynasty (1644-1911),
serious flooding occurred on the Yangtze River 214 times. The 20 th century experienced three immense
floods, two of which, one in 1931 and the other in 1935, flooded 3.4 million and 1.5 million ha of farmland
and killed 145,000 and 142,000 people respectively. Although the 1954 floodwaters of the Yangtze failed
to destroy the Jingjiang dyke and rush into the city of Wuhan, an area of 3.17 million ha of farmland was
inundated, 18.88 million people became victims, and 30,000 others were killed. Direct losses from the flood
reached more than 10 billion Yuan. In addition, the country suffered incalculable, indirect losses from the
flood, such as the Beijing-Guangzhou railway line being unable to offer normal services for 100 days.
The floods of the Yangtze River mainly originate from the Jinsha, Minjiang, Jialing and Hanjiang Rivers,
and the rivers tributary to the Tongting and Poyang Lakes. The main areas of flooding risk are in the