Dams and Impounded Rivers - River Dynamics and Integrated River Management - page 438

1) Dam Structure
As shown in Fig. 7.34 the main buildings of the Three Gorges Project consist of the dam, hydroelectric
station, and navigation structures. The Three Gorges Dam is a conventional concrete gravity type dam:
2,335m long and 175 m high, with its crest elevation at 185 m above sea level. The dam is constructed
from right to left (in the picture) in order: right non-spillway section, ship lift, temporary ship lock (for
construction period), non-spillway dam section, right power plant, right guiding wall, spillway, coffer dam
section, left power plant, non-spillway section. The spillway is located at the central section of the river,
composed of 27 dam blocks with 23 deep outlets (7 × 9 m, with a bottom elevation of 90 m), 22 bottom
outlets (6 × 8.5 m, with a bottom elevation of 56 m) and 22 top outlets (8 m wide, with an elevation of 158 m)
between them. The most striking feature of the project is its gargantuan scale. During the construction of
the Three Gorges Dam, the casting volume of concrete was more than 4 million m 3 in the peak years.
Fig. 7.34 A model of the Three Gorges project on the Yangtze River- from right to left: five step ship locks including
the upper and lower approach channels, the ship lift and its channel, the left power house, the spillway, and the right
power house (See color figure at the end of this topic)
2) Power House and Turbine
The two power plants with 26 sets of power generating units compose a total installed capacity of 18,200 MW
and an annual output of 84.7 billion kwh. The hydroelectric station of the Three Gorges Project is huge and
its total installed capacity ranks number one in the world. The installed capacity of each turbo-generator
of the Three Gorges Hydroelectric Power Station is 680,000 kw. The Three Gorges Hydroelectric Power
Station transmits 500-kV alternating current and -500 kV direct current. The profile of the turbo-generator
is shown in Fig. 7.35. The left power house is 600-m long, 35.5-m wide, and 30-m high with 14 turbo-
generator units. The center of the turbo-generator is at an elevation of 57 m. The turbine diameter is 9.5 m
and the turbine weighs 3,350 tons. The generator is 23 m in diameter and weighs 3,800 tons. The rated
revolution of the turbine is 71.4 revolutions per minute.
3) Navigation Structures
The navigation structure consists of two lines of five step permanent ship locks, a ship-lift, and a temporary
ship lock. The total water head of the permanent ship locks is 113 m. The ship locks enable 10,000 t
ships to pass through. The annual transportation capacity of the locks is 50 million t. The size of the
permanent ship locks is 280 × 34 × 5 m (length × width × the minimum depth over the sill). The upstream
water stage of the ship locks is 135-156 m in the initial period and 145-175 m when the project is completed.