Three Gorges Probe

Keep the reservoir level at 156 metres

Lu Qinkan

September 5, 2003

In a third petition to top Chinese authorities, a leading hydrologist issues an urgent appeal for the design and construction of the Three Gorges project to be re-examined.


On March 3, 2000, 53 Chinese engineers and academics submitted a petition to Chinese authorities, urging that the Three Gorges project be operated with a reservoir water level of 156 metres. This was in line with the 1992 National People’s Congress resolution giving the go-ahead for the dam, and was designed to minimize silt deposits and reduce the number of people who would need to be resettled. Four months later, the experts sent a second letter, in response to a reply from the authorities.

Now, Three Gorges Probe has obtained a copy of a third petition, written by leading hydrologist Lu Qinkan and signed by 42 other experts, which was submitted earlier this year during a national conference of the Communist Party in Beijing, and addressed to incoming and outgoing top leaders.

To: Hu Jintao, General Secretary of the Communist Party of China and Jiang Zemin, former general secretary of the CPC Wu Bangguo, Chairman of the National People’s Congress and Li Peng, former chairman of the NPC Wen Jiabao, Premier of China and Zhu Rongji, former premier Jia Qinglin, Chairman of the Communist Party Central Committee and Li Ruihuan, former chairman of the Chinese People’s Political Consultative Conference

Abstract: The Three Gorges Project Resolution submitted to the National People’s Congress by the State Council in 1992 stated that the project should be operated “in the initial stage at the water-storage level of 156 metres in order to proceed with resettlement plans and to evaluate the impact of silt deposits on navigation and the port at the tail of the reservoir.” However, the designers and builders of the Three Gorges project have ignored this stipulation in the resolution.

Three main problems have yet to be resolved:
1) The discharge of silt by the outlets at the base of the dam;
2) The area affected by the project has been greatly underestimated; and
3) Safety issues related to potential missile attacks on the dam.

The design and construction of the project should be re-examined, and the resolution stating that, “The dam should be operated in the initial stage at the water-storage level of 156 metres” should be heeded, or risk serious consequences.

During the 1992 conference at which the Three Gorges project was approved by the NPC on behalf of the State Council, former vice-premier Zou Jiahua stated that, “The project should be operated in the initial stage at the water-storage level of 156 metres in order to proceed with resettlement plans and to evaluate the impact of silt deposits on navigation and the port at the tail of the reservoir.”

He said that, “Many benefits will be achieved when the reservoir is filled to a height of 156 metres above sea level. The backwater of the reservoir will stretch upstream just as far as Tongluo Gorge and, as a result, Chongqing harbour will not be affected by the deposition of silt.”

Mr. Zou concluded that “filling the reservoir in several stages will provide us with a significant period in which to monitor how silt is deposited in the reservoir, so we can attain a thorough understanding of the issue.”

However, after the dam project got under way, the project’s designers and builders no longer paid any attention to the plan to fill the reservoir in several stages that had been approved by the NPC in 1992. Project officials ignored the resolution on a number of different occasions.

In 1997, for example, He Gong, former deputy general manager of the Three Gorges Project Corp., addressed delegates at the mainland-Taiwan technical conference on the Three Gorges dam, saying that, “The Three Gorges Project will be completed by 2009, with the filling of the reservoir to its normal pool level, or 175 metres above sea level.”

After the 1998 floods, Lu Youmei, general manager of the Three Gorges Project Corp., told Xinhua news agency that, “The flood-control capacity of the TGP will be 22.1 billion cubic metres on completion of the project.” To achieve such a flood-control capacity, the reservoir would have to be filled to a height of 175 metres.

Moreover, in 1999, the Ministry of Water Resources issued a document (No. 41) that stated, “The Three Gorges Project will be operated at the normal pool level of 175 metres by 2009, with a flood-control capacity of 22.15 billion cubic metres.”

We are greatly concerned about three serious issues surrounding the construction of the Three Gorges project, and sincerely hope you will pay more attention to them.

1. Problems with the silt-discharge outlets

At the base of the dam, at an elevation of 56 metres above sea level, 22 outlets have been built to discharge floodwater and silt; each is 8.5 metres high and six metres wide. The outlets will play an important role in discharging floodwater after the reservoir is filled to 135 metres. With a flood-carrying capacity of 35,500 cubic metres, the outlets will be able to release 63 per cent of the floodwater that needs to be discharged at the dam site when the water level is at 135 metres.

According to the project’s original design and schedule, however, all those outlets were to have been sealed with concrete during the 11th to 13th year of dam construction (2003-05). Later the timing of this action was changed to the 13th and 14th year (2005-06). But whatever the schedule, the outlets are to be sealed in the end.

The project’s designers and builders claimed that doing so was necessary to safeguard dam safety. Obviously, sealing the outlets will lead to major problems with silt discharge. With their lower elevation (about 56 metres above sea level) beneath the dam, the outlets are crucial to the process of releasing silt from the reservoir.

We should learn important lessons from past experience. The Sanmenxia dam built on the Yellow River provides a case in point. Sanmenxia was the first and most important project in the comprehensive control and management program on the Yellow River. It was designed to solve the problems of flood control, irrigation, navigation and electricity production in a single project. Sanmenxia was approved by the second plenary session of the first NPC in 1955.

In a discussion about the design of the project in 1957, several water experts suggested that the bottom outlets should be retained on completion of the project to release floodwater and in particular, the silt content. However, project designers ignored the suggestion and claimed that leaving the outlets open would pose a threat to dam safety.

The Sanmenxia dam was completed in 1960 and began storing water. Silt began to build up rapidly in the reservoir, extending to the upper reaches of the river and even threatening Xian city. Premier Zhou Enlai, who chaired special meetings called to discuss the problem, concluded: “While cherishing impractical, grandiose ideas, we failed to deal with an issue properly because we often attached more importance to one side of the issue while ignoring the other.”

With Premier Zhou’s direct intervention, the decision was made to rebuild the dam. Two big tunnels were built alongside the dam, and four steel diversion pipes were introduced to release floodwater and silt. However, as the tunnels and pipes were still too high to flush out the silt that was building up on the bottom of the reservoir, a second reconstruction had to be undertaken. This time, 10 outlets at the base of the dam were opened up with great difficulty, which did help flush out silt because these outlets were located at a much lower elevation beneath the dam. The silt deposits in the lower reaches at Tongguan could be flushed out.

Lessons must be learned from the Sanmenxia dam: It is clear that bottom outlets are important for flushing out silt. And it is very difficult to reopen them once they are sealed.

The [Three Gorges] reservoir has experienced six years of sedimentation since the [Yangtze] river was dammed in 1997, which has provided opportunities for us to monitor how much silt has been deposited and how the silt is distributed in the reservoir. Moreover, after the reservoir is filled to 135 metres in June [2003], we should take the opportunity to conduct more monitoring, especially of how silt will be deposited during the flood season and how the bottom outlets will function. These outlets, at an elevation of 56 metres, below the sluice gates at 90 metres, should be more capable than the sluice gates of letting out more and larger silt. Monitoring data will be valuable for further scientific studies if they are made available through publication in the People’s Yangtze [Renmin Changjiang, an academic publication of the Wuhan-based Changjiang Water Resources Commission].

Not having low-elevation bottom outlets will affect the location, shape and size of sedimentation at the dam site and the silt-regulation capacity of the reservoir as a whole. And more research is needed to establish how the bottom outlets can become worn and even damaged so that timely remedial measures can be taken.

With respect to the operating regime of the bottom outlets, we suggest they should be opened wide in early July, to discharge as much muddy and turbid water as possible, and left that way until the end of October. During the flood season, there is no need to adjust the bottom outlets further, while the sluice gates can be employed to regulate the volume of floodwater.

2. The affected area has been greatly underestimated

In Chongqing municipality, calculation of the number of people affected by the Three Gorges dam should be in line with the official rules, such as those contained in “Regulations for designing and planning in dealing with reservoir inundation” issued by the Ministry of Water Resources. This regulation states that, “The flood-control criteria for important cities affected by reservoirs should be in the range of a one-in-50-year to a one-in-100-year flood” [i.e., a flood of a size that naturally occurs once every 50 to 100 years].

But in Chongqing, the largest city in southwest China, only a one-in-20-year flood was used in calculating the size of the population affected by the reservoir. In reality, the backwater of the reservoir will go as far as Danzishi, Mudong town, 30 kilometres downstream of Chaotianmen, the harbour of Chongqing, when the reservoir has a normal pool level of 175 metres – and many residents, houses, shops, factories, ports and warehouses in urban districts along the Yangtze and Jialing rivers that will be affected have been excluded from resettlement, based on the flawed calculations.

By contrast, in flood-control planning for the Yangtze, a one-in-100-year flood, and even a rare one-in-1,000-year flood, such as occurred in 1870, have been employed in the case of medium and large cities along the middle and lower reaches of the same river valley. The guidelines and methods that have been used to calculate the number of people who will be affected in Chongqing are neither legal nor reasonable.

Based on a report by the Chongqing Flood Control Office in 1986, “The water level in the 1981 flood was observed to have risen as high as 193.38 metres, and the runoff reached 85,700 cubic metres per second at Chongqing’s Xuantanmiao Station. The flood was ranked the third highest in 100 years and a one-in-50-year event. Seven districts in three counties and 137,000 people were affected, while 5,322 hectares of farmland and 857 factories were flooded, causing a direct economic loss of around US$24 million.”

Using a one-in-20-year flood to calculate the population requiring resettlement, the maximum predicted floodwater level would be 183.5 metres – 10 metres lower than that recorded in 1981 in Chongqing – when the reservoir is at its normal pool level (NPL) of 175 metres. There is no doubt that the floodwater level in Chongqing can be expected to be much higher than 183.5 metres. Thus we suggest that the number of people affected by the reservoir be recalculated using the data collected from the survey and monitoring of 1981. A new plan to resettle more migrants should be considered.

Another problem is that the buildup of sediment in the Three Gorges reservoir may raise the backwater level. Based on the Changjiang Water Resources Commission’s calculations in 1986, if the normal pool level is set at either 170 metres or 180 metres, the backwater levels at Cuntan Hydraulic Station [about 20 kilometres downstream of urban Chongqing] will be raised by either 1.64 metres or 3.13 metres respectively after 20 years of reservoir operation.

Based on this calculation, it can be estimated that at an NPL of 175 metres, sedimentation will cause the backwater level at Cuntan Station to be raised by 2.4 metres after 20 years of reservoir operation, which is likely to require the resettlement of an additional 150,000-200,000 people. This estimate just covers the population affected by sedimentation along the main channel of the Yangtze, while the impact on people living along the tributaries of the river has not been taken into consideration. What makes the situation worse is that the number of people affected by this problem may continue to grow over the next 30 or 50 years.

3. Safety issues related to possible missile attacks

Shi Jiayang, chief adviser to the Comprehensive Planning and Water Level Group of the Three Gorges Feasibility Study, has on several occasions raised serious concerns about the dam’s vulnerability to attacks from air-to-surface missiles. He submitted a written report to the State Council, called “A proposal to build the Three Gorges dam with a normal water level of 160 metres for dam safety.”

He wrote: “Missiles have been updated and are much more sophisticated in power and accuracy. No matter how strong the dam structures, the dam is likely to be destroyed and collapse immediately.

“A careful calculation shows that there is a significant difference between building the dam with an NPL of 175 metres and 160 metres. With the NPL at 175 metres or 160 metres, the reservoir will have a storage volume of 39 billion and 26.4 billion cubic metres respectively, and the immediate flood crest would peak at either 1.84 million or 1.5 million cubic metres. Under the circumstances, it would take an average of 6.4 or 3.1 days, respectively, to lower the reservoir to a safe level. The consequences could be very severe if an undeclared war were to start between China and an enemy.”

In the worst-case scenario, we believe, the flood crest could reach as high as 200,000 cubic metres per second in the Zhijiang area [110 kilometres below the dam] after going through a series of narrow gorges and valleys, almost double the rate of the 1870 floods, when runoff was recorded at 105,000 cubic metres a second below the dam. That would seriously threaten the Jingjiang dyke and bring disaster to Hubei and Hunan provinces. This is why we still insist that the Three Gorges dam should be operated in the initial stage at the water-storage level of 156 metres, which will result in less damage and loss if the worst-case scenario does occur.

Allow us to use the last sentence of the 1992 Three Gorges Project Resolution approved by the NPC to conclude this letter. “Further studies are needed and proper solutions should be sought to deal with the problems surrounding construction of the dam project.” For this reason, we suggest that the design and construction of the Three Gorges dam should be re-examined, in seminars and by panels, so that the dam project can be carried out in line with operating it “in the initial stage at the water-storage level of 156 metres, based on the principle of filling the reservoir in different stages.”

Petition writer: Lu Qinkan, adviser to the Flood Control Group of the Three Gorges Feasibility Study and member of the sixth and seventh sessions of the Chinese People’s Political Consultative Conference.

Dated: March 18, 2003

(Translated by Mu Lan, editor of the Chinese edition of Three Gorges Probe.)

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