Dams and Landslides

How to fill the Three Gorges reservoir to 175 meters as planned?

(September 1, 2010 ) Deng Hai, from the New Century Weekly, looks at the never-ending plans involved in managing the Three Gorges reservoir. 

This article was originally published by the New Century Weekly (Xinshiji zhoukan) on Aug 17, 2010. It has been translated by Probe International.

On July 29, 2010 the Three Gorges Project Construction Committee (TGPCC)—acting under the State Council—hosted a conference to discuss when to fill Three Gorges’ reservoir this year. The preliminary plan, decided at the conference, is to begin filling the reservoir on September 10, which is earlier than last year.

Since then, the plan has been sent to relevant government departments, provinces and municipalities for their comments.

According to the original feasibility study for Three Gorges, the reservoir should not begin to be filled before October 1st. But in recent years, that date has been moved ahead: in 2008, filling began on September 28, and in 2009 it started much earlier, on September 15. But both attempts have failed to fill the dam to its official, maximum height, or Normal Pool Level (NPL) of 175 metres.

In 2008, the reservoir water level rose to 172.8 metres, but stopped short of 175 metres because of concerns a higher water level would exacerbate landslides and other geological disasters that were occurring upstream. In 2009, the water level reached 171.43 metres before having to release water to relieve the drought-stricken Hunan and Hubei provinces downstream.

Hu Xinge, director of the operation bureau of the dam authority, says the dam has failed to reach its normal pool level of 175 metres is because conditions around the dam are drastically different than they were in 1980, when the project’s feasibility study was concluded. The inflow of water to the Three Gorges reservoir, for example, has steadily declined— particularly during the months of September and October—due to the construction of other large and medium dams upstream on the Yangtze and on its tributaries in the last two decades. Each year, the demand for water in the middle and lower reaches of the river, downstream of the dam, has also increased.

“Based on the original plan, discharging 5,000 cubic meters/second would have been sufficient during the dry season (typically from October to April) for areas downstream,” Hu Xinge explained. “But the situation is different now, because areas below the dam now have a much higher demand for water to meet local water supply and shipping needs.”

In 2009, the Ministry of Water Resources responded to the problems of managing the conflicting demands of the reservoir by establishing a set of rules for its operation. According to the rules, the amount of water discharged from the reservoir would be at least 8,000 metres/second between the 1st to 10th of October, 7,000 metres/second between the 11th and the 20th, and 6,500 metres/second from October 21st to 31st. If the rate of discharge falls below these benchmarks, water would be immediately passed through the dam unimpeded.

Jin Xingping, head of the Operation Team in the Yangtze River Flood Control and Drought Relief Headquarters and deputy chief engineer of Changjiang Water Resources Commission (CWRC), says that their ability to raise the dam’s reservoir to 175 metres depends on the volume of water coming from upstream on the Yangtze.

Hu Xinge adds that filling the reservoir to 175 metres is likely to become even more difficult in future, because construction of more reservoirs upstream on the Yangtze and its tributaries is scheduled.

Under the circumstances, said Cao Guangjing, general manager of the Three Gorges Corporation, when interviewed by reporters from New Century Weekly, they are likely to start filling the Three Gorges reservoir earlier than expected.

Both former senior government officials and experts seem to agree, having already proposed filling the dam as early as September 1st or the end of August.

But many factors should be considered in filling the reservoir before October 1st: floods, sedimentation and—not least important—ensuring a secure water supply and stable geological environment downstream of the reservoir.

Risk of floods

A study by the Changjiang (Yangtze) River Scientific Research Institute (a branch or research centre of CWRC), the earlier officials begin to raise the reservoir, the less effective the dam is at controlling floods. How this issue will be addressed is absolutely vital.

For example, filling the reservoir in September, means the reservoir would be filled in a month that is traditionally part of the flooding season. According to records from Yichang hydrological station, several major floods have occurred at the dam site in September: on September 4, 1896 when maximum flow reached 71,000 cubic metres/second, 67,500 cubic meters/second on September 5, 1945, and 60,800 cubic meters/second on September 9, 2004.

One proposal wants to start filling the reservoir on September 10 and increase it to 163 metres by the end of September—about five meters higher than the water level in the same period in 2009. But the Ministry of Water Resources says the reservoir should be no higher than 160 meters by the end of September—a much different plan than that being discussed by other government departments, provinces and municipalities.

Hu Xinge says the preliminary calculations show that if officials permit filling to begin on September 10—even in the worst case flood scenario—the reservoir would not exceed 171 metres and so would not affect the dam’s ability to control flooding.

But Jin Xingping cautioned, should the September 10 filling date be approved and implemented, the water level at Shashi city and Chenglingji City—both below the dam—should never be allowed to go above the warning level1 and officials should be vigilant in monitoring weather patterns to ensure that downstream flooding doesn’t occur. This would help officials know if and when water should be released from the reservoir—thereby, acting as a flood control tool for the Yangtze.

“Certainly, in the process, we would also take accurate weather forecasts into account,” says Jin Xingping.

Concerns about silt accumulation in the reservoir

Meanwhile Jinxing Ping warns that the problem caused by sediment deposition must be addressed, even though, “in recent years, little attention has been paid to the issue” because so little sediment has been coming into the reservoir from the upper reaches of the river.

“But the issue of sedimentation is vital,” he says, “because the buildup of silt (in the reservoir) not only affects the safety of shipping in Chongqing, but affects the sustainable use of the reservoir.”

Cao Guangjing agrees, adding that from June 2003 to December 2007, the Three Gorges reservoir had an average rate of sedimentation deposition of 130 million tonnes each year—far below original estimates of 320 million to 350 million tonnes annually for this period.

During the project’s feasibility study, a number of experts expressed concern about sedimentation.

“Professor Huang Wanli in the Qinghua University in particular (was concerned),” Cao Guangjing said. At that time, Professor Huang argued that the final water level of the Three Gorges reservoir should not be more than 156 meters, as it would result in a dangerous buildup of silt and the destruction of the Chongqing Port.

Cao says there was a hidden agenda to the first attempt to fill the reservoir to 175 meters in 2008: dam officials wanted to have a first-hand look at how serious sedimentation would be.

“This is a plan with which we’re able to take the offensive and assume the defensive as the situation requires. It means we can fill the reservoir to its final water level if everything works out, and we also can stop filling if anything goes wrong,” he says.

Hu Xinge is less concerned about the sedimentation issue. She says “the problem (with sedimentation) has been reduced.”

According to Hu, if the Three Gorges reservoir begins filling on September 10 this year, the projected amount of sediment at Chongqing and the fluctuating backwater region over the next 20 years would be equivalent to just two years estimated in the feasibility study carried out in the 1980s.

Security of water supply for downstream area

Filling the reservoir is much more than just a bureaucratic game involving several national and local governments: in fact, it involves trading off conflicting goals of flood control, power generation, shipping, downstream water supply and environmental protection against each other. It is easy to see  why conflicts arise and why plans for the reservoir’s management are complicated.

“Basically, while we are filling the reservoir this year, we are making preparations to fill the reservoir next year, with special reports sent to the Office of the TGPCC,” Hu Xinge told a reporter from the New Century Weekly.

Based on the current and past management of the reservoir, the CWRC begins working in April on the current year’s reservoir filling schedule — that will be implemented seven months later, in October, and last until April of the following year. For example, this year’s proposed filling schedule was completed in April 2010 and addressed several issues such as sedimentation, water conditions, riverbank collapse and so on.

Once a plan is worked out, the CWRC starts preparing a schedule for filling the reservoir beginning in October and lasting until April next year.

This plan will be submitted to the TGPCC after consulting experts and modifying its proposal.  Then the TGPCC will meet with experts for further comments, while consulting with officials from Hubei, Hunan provinces and Chongqing (Municipality), Ministry of Water Resources, Ministry of Land Resources, Ministry of Communications and other provinces and government departments to improve the plan. Finally, it will be submitted to the State Council for approval.

“For the past two years, plans to fill the reservoir have been approved by leaders of the Three Gorges Project Construction Committee,” Hu Xinge said.

After receiving approval, a detailed implementation plan, which needs to be approved by flood control authorities, is made. Throughout the approval process, officials from each province and government department make requests based on their needs. Last year, for example, Chongqing wanted to maintain a relatively high reservoir level—higher than 165 meters in March and 160 meters in April—in order to allow for smooth operations at its port. Chongqing, at the tail end of the reservoir, was concerned about its shipping industry, because last year officials at the dam failed to raise the reservoir to 175 metres, as planned, while they allowed water levels to fall quickly.

Hunan (Province) below the dam, however, wants officials to release more water during the dry season in order to increase water supply at Lake Dongting. Liu Kapo, advisor to the government of Hunan and director of Lake Dongting Water Authority, told the New Century Weekly that the lake area desperately needs water in the dry season because of strong demand from industrial and agricultural sectors.

Mr Liu believes that in future, the Three Gorges project should not focus on flood control, but should also consider regulating water resources and protecting the water environment, as these, particularly the cleanliness of the water, directly affect the lives of people living below the dam.

Jin Xingping highlights that the Three Gorges project is constantly having to meet all of these conflicting interests from both upstream and downstream parties. Even in the dry season, for instance, releasing water too fast causes problems upstream. Because of this concern, the Yangtze River Flood Control and Drought Relief Headquarters has now agreed to fill the reservoir a little earlier—hoping to reduce the problems associated with rapidly changing water levels by extending the duration of reservoir filling as long as possible, thereby raising the water level.

Deng Hai’s article was originally published by the New Century Weekly (Xinshiji zhoukan) on Aug 17, 2010. It has been translated by Probe International.

Further Reading from Probe International:

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