Dams and Impounded Rivers - River Dynamics and Integrated River Management - page 440

Along the right edge of the island a longitudinal dam was built within the coffer dam. The right channel
was deepened and widened by excavation to form an open channel capable of conveying a discharge of
70,000 m 3 /s. The open channel was finished in 1997 and was put into use in May 1997. Ships started to
navigate through the open channel in July, 1997. In the meantime, the temporary ship lock was built on
the left bank of the main channel. The river was not substantially narrowed and floods passed through the
river section smoothly. The permanent ship lock was put into use in this phase.
Phase II (1998-2002) —The beginning of the second phase was marked by the successful closure of
the earth coffer dam on the main channel on Nov. 8, 1997. An enclosed area appeared in the river channel
and the flood water flowed through the artificial open channel, as shown in Fig. 7.36(b). The main dam was
constructed on the river bed within the area enclosed by the coffer dam in the period from 1998-2002. In
the fall of 2002 the main dam and the five step ship locks were completed.
Phase III (2003-2009) —In 2002, the coffer dam on the main river channel was removed by explosion
and water began to flow through the bottom outlets of the dam. The open channel was cut off by a coffer
dam again, as shown in Fig. 7.36(c). On Nov. 7, 2002, the open channel coffer dam was closed. The new
cofferdam was built from elevations of 50 to 140 m and constructed with rolled concrete. It formed a
reservoir in conjunction with the main dam. The water level rose to 135-140 m and the turbo-generators
began to generate electricity. The right part of the main dam was built within the coffer dam. Water flowed
through the 23 bottom outlets of the spillway section. The permanent ship locks and the ship lift were used
for ships to pass through the dam.
Fig. 7.36 Phasing of the TGP construction: (a) phase I—build coffer dam on the right channel, excavate the open
channel and build the longitudinal dam along the right edge of Zhongbao island; (b) phase II—build coffer dam on
the main channel of the river, construct the dam and permanent and temporary ship locks and ship-lift; floods flow
through the open channel. (c) phase III—build coffer dam to close the open channel, construct the right part of the great
dam, impound water to 135-140 m and begin to generate electricity, floods flow through the bottom outlets of the dam