THREE GORGES WATER CONTROL PROJECT
A DREAM OF CHINESE PEOPLE
AB Thapa
China completed the construction of the world's largest dam on May 20, 2006, in Three Gorges area of the Central China's Hubei Province, signifying the accomplishment of the major structure of the mammoth Three Gorges water control project. The proposed Karnali Chisapani Project and the Kosi High Dam Project are also comparable to the China’s Three Gorges Project ( TGP ). Nepal can greatly benefit from China’s experience of implementing the TGP. We can learn that the implementation of a large water resources project has been a great challenge even for a superpower country like China. A small country, like Nepal, must exercise extreme patience as well as caution. We should not rush to compromise optimum development for the sake of a quick deal.
Since a long time the attention of the whole world is drawn to TGP because of the enormity of its size. According to Lu Youmei, President of China Yangtze TGP Development Corporation, the Three Gorges Project has remained as a dream for the China for more than 70 years. Implementation of the TGP was seen as the greatest challenge before the Chinese people and that country has spared nothing to fulfill the ambition of the Chinese people to harness the mighty Yangtze river even though it is taking such a long time.
Planning Stage
The concept of building the Three Gorges Dam Project was initiated early in the last century. Preliminary investigation and planning were done in 1940s'. From the middle of 1950s to present, more than 40 years of extensive efforts have been made into investigation, planning, design and scientific research needed for the implementation of this project. The study covered a wide variety of fields such as the scientific and technical researches, socio-economy and environment protection studies etc.
It has been reported that thousands of engineers and technicians and a large number of experts and scholars from related universities, research institutes and equipment manufacturers from all over the country participated in the study of this project. The experts from all parts of the country were involved on several occasions in course of verification and review of the project. The review work lasted three years from 1986 to 1989 and 412 experts were involved. Since 1940s a large number of foreign experts from countries such as the former Soviet Union, United States, Canada, , Sweden, Italy, Japan, Belgium, Switzerland, Germany, France, Brazil, etc., have also participated in the research and consultation works.
The major components of the project consist of the dam, two power plants and navigation facilities'. For a long time, experts were involved in the in-depth studies and researches on various alternatives to determine the type, configuration and layout of the structures. And it was only after successfully completing the full analysis based on scientific studies and testing in various fields, such as hydraulics, sedimentation, structure and material, etc., the final decision was made to approve the project.
Completion of Engineering Studies
The feasibility study report was completed towards the end of 1989. An overall review of the feasibility study was done by the Three Gorges Project Examination Committee of the State Council. In April 1992, the Fifth Session of the 7th National People's Congress passed the resolution to implement the Three Gorges Project. In December of the same year, the preliminary design report of the Three Gorges Project on the Yangtze River was also completed, and it was formally approved in July 1993 by the Three Gorges Project Construction Committee (TGPCC) of the State Council.
The technical design included major structures such as the dam, powerhouses, permanent shiplock, vertical shiplift, 2nd stage upstream cofferdam, mechanical and electrical equipments &. facilities, project safety monitoring, habour/piers and navigation channel regulation in the fluctuating backwater region (including effect of the degradation of the river bed downstream and the countermeasures thereto). In the final design the spillway is placed at the center of the river channel, i.e., on the original main river course, while the intake dam sections and non-overflow dam sections are arranged on its both sides. The powerhouses are placed on the back of the intake dam. The permanent navigation structures are located on the left bank side
Premier LiPeng Declared the Formal Start
On April 3 of 1992, the fifth session of 7th National People's Congress passed the resolution on the construction of the Three Gorges Project, which marked the end of the 40-plus-year verification phase and the start of the performance phase. With the first batch of construction teams entering into the site in the early 1993, the implementation of preparatory works and the stage I diversion works started. On Dec' 14, 1994, Premier LiPeng declared the formal start of TGP's construction at the dam site.
The Dam
After repeated study and analysis of 15 dam site alternatives, the site for TGP was finally selected at Sandouping where the dam foundation would be resting on crystalline rock. The total water catchment area hereof is about one million km2 with 451 billion m3 of average annual runoff and 526 million tons of annual sediment discharge.
The dam is of a concrete gravity type. The total length of the dam axis is 2, 309 m, with the crest elevation at 185 m and a maximum height of 175 m.
The spillway dam, which is located in the middle of the river channel, is 483 m long, where there are 23 bottom outlets. Surface sluice gates with a net width of 8 m have been provided. There are flip buckets in the downstream part for energy dissipation. With a maximum discharge capacity of 116, 000 m3/s, the project is able to cope with any possible maximum flood.
Power Stations
Being provided with a total installation of 18, 200 MW generating capacity the TGP will supply a large proportion of its electricity to East China, Central China, and a small proportion to the east Sichuan province and Chongqing Municipality. This means a replacement of 40 to 50 million tons of raw coal combustion each year. And this reliable, cheap and renewable energy will play a very important role in the development of economy and prevention of environmental pollution.
According to the plan, two powerhouses would be placed at the toe of the dam, one on each side. In the left powerhouse, about 643.6 m long, 14 sets of turbine generator units would be installed, while in the right one, 584.2 m in total length, there would be 12 turbine generator units. Thus, there would be 26 sets of turbine generator units in total (the turbine will be of Francis type), 700 MW each, totaling 18,200 MW in total installed capacity.. There would be 15 transmission lines. Central China and east Sichuan Province would be connected with the Three Gorges Project by 500 KV AC lines, and East China. By I 500 kV DC lines.
On the right bank, enough room has been preserved for future underground powerhouse to be equipped with 6 turbine generator units with a total 4, 200 MW installed capacity. The intakes of these units will be constructed now simultaneously with the rest of the project.
Navigation Facilities
The 660km long waterway from Yichang City to Chongqing Municipality would be greatly improved after the completion of the TGP reservoir, making it possible for 10, 000 tons barge fleet to sail upstream directly to the harbour of Chongqing. It is expected that an increase of annual one-way navigation capacity from present 10 million tons to 50 million tons, and a decrease of the navigation cost from 35 % to 37 % would be reached. With the regulation of the Yangtze runoff, the minimum flow downstream Yichang in the dry season would be increased from the present 3,000 m3/s to over 5, 000 m3/s, which would improve the navigation in the middle reaches of the Yangtze River.
The permanent navigation structures consist of a permanent ship-lock and a ship-lift. The ship-lock is a double-way five-step flight lock, and each lock chamber is 280m x 34m x5 m in size which is adequate to pass 10, 000 tons of barge fleet.
The ship-lift is designed as a one step vertical hoisting type with a container 120m x 18 m x 3.5 m in size adequate in capacity for carrying one 3,000 ton passenger or cargo boat each time.
Scheduling
The master schedule of TGP is arranged as hereinafter: (1) Preparation and 1st stage construction - 5 years from 1993 to 1997 (2) 2nd stage construction- 6 years from 1998 to 2003 (3) 3rd stage construction- 6 years from 2004 to 2009.
The total duration of construction will be 17 years taking into account the time for preparation. The main course of the river was to be closed in 1997, and the initial two turbine-generating units was to be put into operation in 2003 (the 11th year). The whole project will be completed in the year of 2009.
Sediment Study
Sediment control is one of the major technical problems to be tackled. Since 1950's, many research institutes and experts have conducted extensive studies on this issue in China. Their findings have been published in many international journals. The successful experience gained from the Gezhouba Project on sediment management has provided solid foundation for the sediment study of the Three Gorges Project.
Comprehensive research methods, such as prototype observation, mathematical model computation, physical model tests, and analogue analysis on existing projects have been adopted for the TGP's sediment study. The results show that the sediment problem of the TGP is resolvable based on the studies conducted in the past by sediment experts in China and aboard.
Discharging the Turbid and Impounding the Clean
The Yangtze River is abundant in runoff' The Three Gorges Dam is to be equipped with 23 bottom discharge outlets at low elevation (90 m). Meanwhile, the reservoir level in the flood season will be maintained at a fairly low elevation (145 m). These two characteristics allow the application of a strategy of reservoir operation summed up in China as "discharging the turbid and impounding the clean' . During the flood season from June to September, when the river carries 84% of the annual sediment load and 61 % of the annual runoff, the reservoir draws down to a 145m level that creates a condition in favour of sediment sluicing, allowing a large discharge of sediment out of the reservoir from the bottom outlets. At the end of the flood season (October) when there is less sediment content in water, the reservoir will be impounded to 175 m level for enhancement of power generation and navigation. Chinese experts are hoping that in this operation manner, most of the sediment will be discharged, the large part of sediment deposited will remain in the dead storage of the reservoir, and most part of the effective storage can be preserved permanently. .
