The Bane of Three Gorges Dam

Discussion in 'China' started by Daredevil, Aug 12, 2011.

  1. Daredevil

    Daredevil On Vacation! Administrator

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    The Bane of Three Gorges Dam

    The travails of the Three Gorges Dam are a cautionary tale for Laos and its Southeast Asian neighbors as they wrestle with the pros and cons of damming the lower Mekong River.

    BEIJING—Scientists predicted that when the world's largest hydropower project came online in 2003, it would be an environmental bane. The Three Gorges Dam on the Yangtze River has unfortunately lived up to expectations. For that reason China is embarking on a 10-year mitigation effort that sources say will cost $26.45 billion.

    The travails of the Three Gorges Dam are a cautionary tale for Laos and its Southeast Asian neighbors as they wrestle with the pros and cons of damming the lower Mekong River (see main text). Two consequences have proved worse than anticipated: deteriorating water quality and erosion. And the potential for spreading a snail-borne disease apparently wasn't even on planners' radar.

    The decision to build the dam in 1992 came after decades of study and fierce internal debate. Benefits such as power generation and flood control are indisputable. But leaders also knew that the costs would be enormous. The newly created 1080-km2 reservoir submerged wholly or in part 13 cities and 466 towns, displacing roughly 1.3 million people, and triggered thousands of landslides. The reservoir wiped out fish spawning areas and raised an impassable barrier to one endangered mammal—the Yangtze finless porpoise—and two species that were in terminal decline: the Chinese river dolphin, or baiji, and the Chinese paddlefish (Science, 1 August 2008, p. 628).

    Before the Three Gorges Dam began holding back the river in 2003, local Yangtze water by national standards was suitable for drinking. Not anymore. In the past several years, toxic algal blooms have regularly blighted 22 tributaries. Slower tributary flow due to the reservoir and a surfeit of nutrients from land-use changes are to blame, a team led by Fu Bojie, an ecologist at the Research Centre for Eco-Environmental Sciences of the Chinese Academy of Sciences in Beijing, reported last year in Progress in Physical Geography. A second scourge, they say, is increased heavy metal pollution.

    Erosion, too, was underestimated. Because sediments accumulate in the reservoir, water released through the dam's turbines is relatively clear. Sediment-light water scours riverbanks to a degree that “is much higher than the designed and expected levels,” Fu's team states. Severe erosion has caused some riverbank sections to collapse.

    Another headache is schistosomiasis, known as snail fever in China. As many as 1 million Chinese are infected with the parasitic trematode, transmitted by Oncomelania snails. In endemic areas near lakes and wetlands in the Yangtze River Basin, prevalence hovers around 5%. The Three Gorges Dam increased the snail's habitat—and the infection risk. China's health ministry is improving sanitation and implementing other measures in a bid to reduce the infection rate to less than 1% by 2015.

    In May, the State Council announced a massive effort to rein in other potential harms—stabilizing river flow, reinforcing levees, improving water quality—and boost livelihoods of displaced people. “The fact that the government openly acknowledged negative impacts was a significant change toward more openness,” says Lars Skov Andersen of the E.U.-China River Basin Management Programme in Wuhan.

    Since then, however, few details have come to light. One researcher who studies the new reservoir's impact on plant populations told Science that he has been ordered to deliver his reports to the government and cannot speak publicly about his findings. The official authorized to speak to the media was unavailable before Science went to press.

    Secrecy aside, observers are confident that the initiative will have a robust scientific component. Some research lines may break new ground: for instance, probing habitat fragmentation after the reservoir turned dozens of hilltops into islands. But many findings are expected to be a sobering reminder that a big dam can bring unexpected consequences
     
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  3. amoy

    amoy Senior Member Senior Member

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    Colossal lift for ships tested at Three Gorges
    By Xinhua in Wuhan (China Daily)Updated: 2016-09-20 07:09

    Trial operation of a permanent ship-lift at the Three Gorges Dam in Hubei province began on Sunday, marking the completion of the Three Gorges project 22 years after construction began.

    The lift, designed by a Chinese and German team, is the largest and most sophisticated in the world, according to Three Gorges Co, the State-owned company responsible for construction.

    The vertical-hoisting elevator is designed for small and medium-sized ships - those with a maximum displacement of about 3,000 tons - to traverse the dam. The water level behind the dam may be as much as 113 meters higher than the river.

    [​IMG]
    Aerial view of the Three Gorges Dam ship lift (file photo)



    [​IMG]
    the adjacent five-tier ship lock

    The lift is equipped with a ship-chamber, which contains a pool of water 120 meters long, 18 meters wide and 3.5 meters deep. The chamber, its mechanical systems and the water weigh 15,500 metric tons altogether.

    The lift has been installed to complement the adjacent five-tier ship lock, which is also the world's largest. It has allowed ships to pass through since 2003.

    The lock is currently running at full capacity, with cargo throughput of 119.6 million tons in 2015 - a massive increase over its 34.31 million tons a decade earlier. The increase has been attributed to the booming water transportation sector along the mountainous regions of the Three Gorges, including Chongqing municipality.

    It once took a ship about three to four hours to pass the dam via the lock. The lift will cut this time to between 40 minutes and one hour.
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    The Three Gorges project is a multifunctional water control system, consisting of a 2,309-meter long and 185-meter high dam, a five-tier ship lock, 32 hydropower turbogenerators and the new ship-lift.

    The lift was in the original plan passed by the National People's Congress, China's top legislature, in 1992. Because of technical and safety concerns, that part of the project was put on hold in 1994.

    By the end of 2009, all other construction work at the dam had been completed.

    The original plan was to build a lifting mechanism based on a wire-rope hoist. Experts, however, were concerned about its colossal scale and feared the tank used to carry vessels would be unstable, said Lu Youmei, former general manager of China Three Gorges Corp.

    In 2003, gear mechanisms and nut-screw safety measures from Germany were introduced to replace the original plan, and work resumed in 2008.

    The new approach helps keep the lift balanced and is far superior to the wire-rope hoist method, said Lu, who is also an academic with the Chinese Academy of Engineering.

    Over the past eight years, many advances have been made. New standards were set for steel smelting, civil engineering and management, thanks to the construction of the ship-lift, said Wu Xiaoyun, deputy director of the mechanical and electrical engineering department of Three Gorges Co.

    Boosting the shipping capacity of the Yangtze, China's longest river, was one of the three major purposes of the Three Gorges project, along with flood control and power generation.

    Before the creation of the Three Gorges reservoir in 2003, the upper reaches of the Yangtze were off-limits to big vessels
    , as the river was too narrow and shallow, and its many winding and turbulent stretches - known as "ghost gates" - were dangerous for small boats.
    [​IMG]
     
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