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China's Three Gorges Project And Nepal By AB Thapa It has very
recently been reported that the bottom
outlets of the Three Gorges dam has
been closed and the filling of the
reservoir started. Thus the construction of
the Three Gorges Project entered into its stage-3.
The completion date of the construction works of
this giant project that started more
than ten years ago is still far off.
It is scheduled to be completed after
six years from now. Mr. Lu Youmei,
President of China Yangtze Three Gorges Project
Development Corporation writes that the Three
Gorges Project has been a dream for
the Chinese people for more than 70 years as
it is a key part of the scheme for
harnessing and development of the Yangtze
River. Chinese people's relentless efforts
over a very long period to harness
the Yangtze River could serve us as a
reminder that we too should take very
seriously the development of our water
resources since the projects to build
dams on Karnali or the Kosi
rivers are almost comparable to the
Three Gorges Project in magnitude and
also in complexity. Needless to say
that our impatience in handling our large
water resources projects could turn out to
be extremely disastrous to our country
Unfortunately most of us including our
decision makers and also the press are
not really serious even to keep
ourselves well informed about the
water resources related matters. It
really looked ridiculous and at the
same time annoying when a person
who had served as the head of
the water resources related ministry
for quite some time in Nepal was
saying not once in a radio debate
on India's water linkage project that
Nepal is the second richest country in
the world in hydropower resources.
Any common person would not have much
difficulty to guess that the big
countries like the China, Russia, USA and
India were sure to have by
comparison with Nepal far bigger
hydropower potential. Neither the other
water resources experts participating in the
debate nor the convener of the debate
on behalf of the FM radio saw
anything wrong in that statement. The Yangtze
River Dam The Yangtze
is the longest river in China and the third
largest in the world. At the dam site,
the Yangtze brings an annual runoff of
438,000 million cubic meters, and an annual
sediment discharge of 526 million
cubic meters. The Three Gorges Project
is located at Sandoupin in Hubei
Province 1300 km from Shanghai and 660 km
downstream from Chongqing. The 660 km
long Jingjiang Section in the middle
reach of the Yangtze has been under
serious threat of flooding. The dykes
along this stretch of the river protect
more than 15 million people, 1.56
million hectares of farmland and many
industrial sites. At present these dykes
breach whenever there is a flood
greater than the one occurring once in
ten years. Such floods result in a
major disaster. After the completion of the
Three Gorges Project, the flood control
capacity of the Jingjiang Section could
be raised from 10-year to once in
100-year flood. The Three
Gorges Project consists of a 175 m high
concrete dam, two power plants, and a
system of navigation facilities. The spillway
dam section is located on the middle
of the original main river channel, flanked
by the power plant and non-spillway dam
section, one on either side. The two
power stations are at the toes of their
respective dam sections. At the right
bank there is room for an additional
underground power plant to house additional
generation units when the development is
expanded later. Located on the left
bank are the permanent navigation structures. The spillway
section of the dam has a total length
of 483m. To facilitate sediment flushing and
discharging high floods, there are 23 deep
outlets and 22 surface bays. Each of
the deep outlets has a dimension of 7m
by 9m. The surface bays have a
net width of 8m. At the downstream
end of this section, a trajectory
bucket is provided as an energy dissipater.
The maximum flood-releasing capacity of the
project is 113000 cubic meters/s. Upon completion,
the Three Gorges Project would become the
largest hydropower station in the
world, with a total installed capacity
of 18,200MW and annual energy output
of 84710 GWh from 26 sets of 700 MW
generating units. The power generated would
be fed to central and eastern China.
Inland navigation is a very important
component of the Three Gorges Project. Gezhouba
Reregulating Dam The Gezhouba
project is a component part of the Three
Gorges Project. Its reservoir is to function as a reregulating
pool and a downstream navigation step for the
Three Gorges Project. China decided to construct
the Gezhouba dam before the Three Gorges Project
for a number of reasons: to improve the navigation
conditions of the gorge stretch; to produce
hydroelectric power to meet the urgent
demand in the area. Inland Waterway Inland waterways
were very much developed in China
from the time immemorial. Chinese had even
built impressive canals between 3rd century
BC and the Ist century AD. Outstanding were
the Ling Ch'u in Kuangsi, 90 miles long from the
Han capital; Ch'ang-an to the Huang Ho; and
the Pien Canal in Honan. Of later canals the
most spectacular was the Grand Canal, the
first 600-mile section of which was opened
to navigation in 610. This waterway enabled
grain to be transported from the lower
Yangtze and Huai to K'ai-feng and Lo-yang. China's
past and recent experiences of
developing inland navigation by using
natural as well as artificial channels
could be of great interest to Nepal
as well India since both the
countries, Nepal and India, have
decided to carry out jointly a detailed
study of the Kosi navigation canal
linking Chatra in Nepal with the Ganges
waterway. In recent
years the Yangtze river is extensively
used for water transportation. The capacity
of the Yangtze river waterway
constitutes 78% of the China's total
inland rivers transportation capacity. Despite
such extensive uses, the navigation condition of
its natural course could not fully meet
the growing requirements of China's fast
growing economy. There were bottlenecks from
Chongqin in Sichuan province to Yichang in
Hubei province. Here, the river flows
through an area of high mountains and
deep valleys, with considerable turbulence
and dangerous shoals, which had limited
the development of the Yangtze waterway.
Upon completion of the Three Gorges Project, the
reservoir backwater would reach Chonqin and the
annual transportation capacity for freight would
be increased to 50 million tons, with costs
reduced by 35-37 percent. For half of
each year when the reservoir water
level is high, 10000 ton ships would
be able to sail right up to the
Jiulongpo port of Chongqing. During dry
seasons, the navigation conditions of the
river downstream of the dam will also
be improved, due to an increase in the
low water flow. Permanent
double-line locks would be provided as
the main navigation facilities after
the project is commissioned. The locks
would meet the requirements of a
single direction downstream freight volume
of 50 million ton, the projected volume for
the year 2030, and they would allow passage
of 10000 ton ship fleets. A vertical
ship lift is also provided as an
express passage for passenger traffic and also for
certain specific types of ship. Permanent
Navigation Locks The permanent
locks comprising large-scale, multi-step structures
would be provided, with the highest total
head of any lock now in operation
or under construction anywhere in the
world. The effective lock chamber dimensions
of 280m x 34m x 5m have been adopted. The
minimum dimensions of the approach channels are
controlled as follows: length of straight approach line
entrance 930m, radius of bends 1000m, bottom width
180m, minimum upstream water depth 6,0m and
minimum downstream water depth 5.5m. The maximum
allowable river flow for navigation is 56700 cu.m/s,
with allowable maximum water velocity at the
mouth of 2.0m/s (longitudinal) and 0.3m/s (transverse)
and 0.4 m/s (back flow). The double-line
five-step flight locks are situated on the left bank.
The length of the main navigation structures is 1607m, with an
upstream approach channel 2113m long, downstream
approach channel 2722m, and a total lockage route length
of 6442m. Mitre gates are used to operate
the lock. The height of the mitre gates
at lock heads 1 and 2 is 37m and at lock heads 3
ñ 6 it is 39.75m. During opening/closing, the
maximum submerged depth of the gate at the
first lock head is 35m. At the first
lock head, the filling valve is of
the normal tainter type and at lock heads 2
-6, all are reversed tainter gates. The method of
operating the double-line lock under normal
conditions is that one line carries
up bound traffic while the other down bound
traffic. During the periods when one lock is shut
down for repairs, the other line of locks passes
traffic in one direction, changing over to pass
the traffic in the opposite direction at
specific intervals. The filling or emptying
time for the Three Gorges Project lock
chamber would be 12 ñ 13 min. The
time interval( or cycle time) for successive
groups of ships to pass through would
approximately be one hour. Annual one-way capacity
would amount to 51.52 million tons. Transit
time for a group of ships to pass
through the five flight ship locks would be
2.35 hours and the transit time for a group
of ships, from entering the mouth of an
approach channel to leaving the mouth of
another approach channel is expected to be
3.14 hours. Annual water consumption, excluding
flood season, would amount to 1.7 billion
cubic meters. Vertical Ship
Lift Layout The ship lift of the
Three Gorges Project is a counterbalanced vertical
ship lift with steel cable
hoists, with effective dimensions of 120m x 18m x 3.5m,
the same as those of the Gezhouba No.3 lock. The weight
of the ship caisson with water is 11800 tons. It
can carry a large passenger cargo vessel,
a single barge group, consisting of a 1200HD
tug and a 1500 ton barge, or a single barge of
around 3000ton. Temporary ship lock
has been provided to continue navigation
even after the Yangtze river course is
blocked by coffer dam. The temporary lock
consists of upper lock head, lock chamber,; lower
lock head, upstream / downstream approach
channels. The effective dimensions of the lock chamber
are 240m x 24m x 4m. A Lesson
To Learn The volume of the Three Gorges Project storage reservoir is too small to handle the enormous volume of the Yangtze river sediments. It would not take long time to fill up the reservoir. China has made considerable headway with the studies to find ways to preserve the live storage volume of the reservoirs. Their findings are reported in the Journal of the Hydraulic Research published by the American Society of Civil Engineers of the USA. It is being said that the unique mode of the Three Gorges reservoir operation, in particular the low pool level release of silt-laden normal flood under possibly the largest water surface gradient allows most (85%) of the live storage between minimum operating level and the full supply level be preserved for permanent use. In Nepal we could expect to encounter a similar problem in planning the Sunkosi-1 high dam despite the fact that it is a far smaller river by comparison with the Yangtze river. Needless to say that in future the information on the Three Gorges Project reservoir operation would be very valuable to us in planning the Sunkosi-1 or any other similar projects. |
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