China's Dams

Climate change a dam smokescreen?

(November 20, 2012) Poyang, China’s largest freshwater lake, is experiencing a dramatic drop in water levels as a result of drought exacerbated by the effects of ongoing climate change — a dry-up that began in earnest in 2003, according to a report published by China’s state-run Xinhua news agency earlier this year. What the report doesn’t acknowledge is that 2003 also coincides with the year reservoir filling began at the Three Gorges mega-dam 500-km upstream of Poyang, on the Yangtze River. Responding separately to Xinhua’s claims, noted Chinese geologist and environmentalist Fan Xiao points to operations at the dam, as well as rapid development of the Yangtze’s upper reaches, as the culprits behind the distressing changes Poyang and other Yangtze tributaries are experiencing: expect worse, he warns, but not because of climate change.

Saving China’s largest freshwater lake,” published by Xinhua/China Daily on August 27, 2012, reports that a lack of rainfall is shrinking Lake Poyang, in the eastern Chinese province of Jiangxi.

Cracks a fist wide fragment the lakebed of Poyang Lake in east China’s Jiangxi Province, on Jan. 5, 2012. Poyang Lake is fed by five rivers in the province and empties into the nation’s longest river, the Yangtze. [Xinhua/Zhou Ke/China.org]

Throughout the spring and summer of 2011, Lake Poyang and surrounding areas were punished by the worst drought to hit the region in 60 years. The drought completely dried out Poyang, leaving the lakebed arid and cracked in parts wide enough to insert a hand; fish stocks are estimated to have plummeted by more than 60 percent.

Citing data from Jiangxi’s provincial hydrographic bureau, Xinhua reports that the lake’s water level had plunged from its highest level for 2012 (at the time of publication) from 19.65 meters to 17.71 meters, as of August 26. According to bureau statistics, the average precipitation in Jiangxi for 2011 was 21 percent lower than the area’s annual average for the past several years, says Xinhua. Less rainfall, it noted, in combination with aggressive sand dredging and tourism-related exploitation had reduced the size of Lake Poyang from 4,000 square km to about 200 square km.

Xinhua referred to Wang Hao, a water conservancy expert with the China Institute of Water Resources and Hydropower Research, for further insight:

“Poyang has been drying up over the past decade, particularly from 2003 to 2008,” said Wang. “During that time, its annual runoff was 23.2 billion cubic meters, or 15 percent, less than the average of previous years.”

Wang said the situation is likely to worsen due to the growing threat of climate change, which has been blamed for the lake’s decreasing water level alongside human activity.

Wang did concede that dam activity at Three Gorges, and other projects located along the Yangtze’s upper reaches, had caused Lake Poyang’s dry season to arrive prematurely. To ease the strain, he told Xinhua:

“A water conservancy project is needed at the mouth of Poyang, where water from the lake flows into the Yangtze River. The project could maintain water levels during the dry season and won’t disturb water flows during the flood season.”

The article’s publication prompted a detailed response from Chinese geologist and environmentalist Fan Xiao, who argues that nature is not responsible for the devastating water shortages: the Three Gorges dam is. Fan contends that a drop in rainfall does not explain Lake Poyang’s periodic dry-ups dating back to 2003. The precipitation trend for the area actually shows an annual increase, he says, referring to a report on the conservation and development of the Yangtze. The report, compiled by the Chinese Academy of Sciences, found no significant changes in annual precipitation for the Yangtze basin overall, including its middle and lower sections, for the past ten years, with the exception of an annual increase for those parts of the river and its source.

Fan also dismisses the claim that illegal sand excavation and pollution are contributing factors to Lake Poyang’s dramatic dwindling. He said sand mining of the lakebed would only deepen the lake’s basin and make the flow of water out of the lake more difficult. Pollution due to tourism, on the other hand, would affect water quality but not the lake’s water levels.

Fan instead highlighted the severe build-up of sediment behind Three Gorges dam. Sediment (including nutrients promoting species and habitat survival) that would normally flow down the Yangtze and into downstream deltas and estuaries is now trapped. Meanwhile, the resulting silt-load reduction in water flowing out of the dam raises the pace of the water’s flow and that momentum has produced an increased “scouring” effect, he says. The quicker flow is eroding the Yangtze’s middle and lower reaches, undercutting its riverbed and is a major cause, asserts Fan, of declining water tables below the dam.

Referring again to data published by the Chinese Academy of Sciences, Fan said from October 2003 to October 2007 alone, the effects of scouring had deepened the Yangtze and widened the elevation difference between the Yangtze’s riverbed and the lakebeds of both Poyang and Dongting, which not only made it more difficult for the Yangtze to supply those lakes with water, but had also accelerated water flow from Poyang and Dongting into the Yangtze.

The completion of more and more dam projects in the Yangtze’s upper reaches would only aggravate the current situation, said Fan, and intensify environmental crises in downstream sections of the river.

Meanwhile, adding another dam to the mouth of Poyang to hold water within the lake, as suggested by Wang Hao, was “foolish,” said Fan. It would further impede the exchange of water between the Yangtze and its tributaries, cut off ecological corridors for aquatic organisms in both areas, create ecological disasters for instance, the flooding of wetlands –  and speed up water quality deterioration, he said.

Sediment is not the only problem. By withholding water for power generation, the Three Gorges dam further deprived downstream areas of water. Fan points out that in 2003, when the dam was first filled to 135 metres, and from then onwards, outflow from the dam’s reservoir has dropped noticeably and, over time, has led to a dramatic decline in the volume of water entering great lakes, such as Poyang and Dongting.

Writes Fan:

Thus, in the past decade, the periodic drying up experienced by Lake Poyang and Lake Dongting has been due mainly to the impounding of the Three Gorges project on a yearly basis. The deepening of the riverbed was caused by increased scouring in the main channel of the Yangtze River downstream of the Three Gorges dam. The dam has played an important role in the periodic drying up of Lake Poyang and Lake Dongting.

To help remedy the situation, Fan says better coordination between the Yangtze’s upstream and downstream management teams would improve the Three Gorges dam’s capacity for flood-control and its regulation of water levels during the flood season. Increasing sediment discharge out of the dam reservoir would mitigate the current scouring scourge to areas downstream of the dam, he said. Fan also recommended lowering the reservoir’s water level during impoundment and decreasing the speed of impoundment, as well as increasing downstream water discharges after the flood season to ensure basic demands for water were met.


Fan Xiao’s response in full to the China Daily article, Saving China’s largest freshwater lake

September 2, 2012

The Xinhua article mentioned the concerns voiced by fishermen in Lake Poyang: it is still the flood season, but water levels in the Lake Poyang area have plummeted significantly over the past two weeks – an event which has become more common in fall, winter and early spring every year for the past few years. By quoting data from the Hydrological Bureau of Jiangxi Province, the author of the article said that the decline in rainfall was responsible for the dropping of water levels in the Lake Poyang area, as well as its periodic dry ups in recent years. For instance, that  annual precipitation in 2011 had dropped by 21% compared to average rainfall for the area over the past few years. But this data does not explain the periodic dry-up phenomenon Lake Poyang has experienced for the past decade. According to the Report on the Conservation and Development of the Yangtze, compiled by the Chinese Academy of Sciences, there have been no significant changes in annual precipitation for the Yangtze basin as a whole – including its middle and lower reaches – over the past decade, within plus or minus 5% of the rate of change. Even in that regard, there has been a trend towards increased annual precipitation for both the source of the Yangtze and the river’s middle and lower reaches.

This article also mentioned that along with a decline in precipitation, illegal sand excavation of the lakebed in addition to pollution caused by tourism, are also contributing to the dramatic shrinkage of the Lake Poyang area. However, there is no ground or sufficient evidence for this claim. First of all, as mentioned above, there is no meteorological observational data to support the argument that precipitation has continued to decline in the lake area over the last 10 years. Second, sand mining Poyang’s lakebed to a significant extent would deepen the lake basin, and this in turn would make water flow out of the lake more difficult. But what we currently see are massive amounts of water flowing from the lake to the Yangtze in an accelerated manner. Finally, pollution caused by tourism would affect the lake’s water quality but there would be little effect on the dropping of the lake’s water level.

The author of the article has cited Wang Hao, a water expert from the China Institute of Water Resources and Hydropower Research and a member of the Chinese Academy of Sciences, as saying that the Three Gorges dam and other projects built in the Yangtze’s upstream areas caused the lake’s dry season to arrive earlier than usual. Meanwhile, Mr. Wang pointed out that Lake Poyang has been drying up over the past decade, particularly since 2003. Furthermore, Mr. Wang has also suggested that a water conservancy project is needed at the mouth of Poyang, where water from the lake flows into the Yangtze. He says, the project could maintain water levels in Lake Poyang and prevent water flowing from Poyang into the Yangtze during the dry season.

But what I have to point out is that the Three Gorges project started filling the Three Gorges dam reservoir in the year of 2003 for the first time, when it was filled to 135 metres, then to 156 metres in 2006, and 172 metres and higher in 2008, and so on. It was from the very beginning of the impounding of the Three Gorges dam reservoir that the outflow from the reservoir was as low as only 50% of the inflow between September to November of each year, which led to a dramatic decline of the amount of water from the Yangtze entering great lakes such as Poyang and Dongting which are connected to the Yangtze, compared to the natural state (before the construction of the dam).

Meanwhile, a large amount of sand had been deposited in the Three Gorges reservoir and had created a block. As such, clean water discharged from the reservoir produced a strong scouring and erosive effect as it traveled through the middle and lower reaches of the Yangtze, resulting in a deepening of the riverbed and a continued drop in river water levels below the dam. According to data released by the Report on the Conservation and Development of the Yangtze, from October 2003 to October 2007 alone, the total amount of scouring reached 550 million cubic metres in the river section from Yichang to the mouth of Lake Poyang, with the greatest depth of scouring reaching 13 metres on the riverbed section of Jiangjiang River near the shore (below the dam), greatly exceeding original estimates. The increasing deepening of the Yangtze’s riverbed has widened the elevation difference between the riverbed and the lakebeds of Poyang and Dongting, not only making it harder for the Yangtze to supply water to these two big lakes, but also accelerating water flow from both Poyang and Dongting into the Yangtze.

Thus, in the past decade, the periodic drying up experienced by Lake Poyang and Lake Dongting has been due mainly to the impounding of the Three Gorges project on a yearly basis. The deepening of the riverbed was caused by increased scouring in the main channel of the Yangtze River downstream of the Three Gorges dam. The dam has played an important role in the periodic drying up of Lake Poyang and Lake Dongting.

Human overdevelopment and excessive intervention to natural rivers and their ecosystems through the construction of more and more engineering projects have resulted in the deterioration of the water environment and river ecology. The idea of building a dam at the mouth of Poyang to hold water within the lake in order to solve the problem of drying up is nothing but a foolish one: the proposed dam will result in not only the impediment of water exchange between the lake and the Yangtze, but will also cut off ecological corridors for aquatic organisms in both the lake and the river, leading to a series of ecological disasters such as the flooding of large areas of wetland, and the rapid worsening of water quality in Lake Poyang because there is no water exchange with the Yangtze anymore.

As stated above, building the Three Gorges project is the main reason for the periodic drying up of both Poyang and Dongting lakes. And with the completion of more and more hydro dams in the upper reaches of the Yangtze, the situation will get worse and the environmental crisis in the middle and lower reaches of the Yangtze will intensify. Therefore, it is really important to do a good job of taking the whole situation into account and to coordinate the different management departments upstream and downstream of the Three Gorges dam to work together to: lower and maintain the flood-control limit of water levels during flood season, so as to increase the capacity of the dam to discharge sediment out of the reservoir and to mitigate scouring of the riverbed in the river’s middle and lower reaches; to lower the water levels of reservoir impoundment, slow down the speed of impoundment, and increase the outflow in the period after the flood season, so as to ensure basic needs and demands for water are met in the middle and lower sections of the Yangtze River below Three Gorges dam.

Further Reading

Did the Three Gorges Dam create China’s devastating drought?

The Yangtze runs dry

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