Three Gorges Probe

Updated: Three Gorges Dam reservoir reaches 175m

(October 31, 2011) New update The Three Gorges Dam reached full capacity at 5 pm on October 30, for the second time since its construction. An official stated that twelve turbo-generator units came online on Sunday, with a capacity of 8.2 million kw. Xinhua’s report of the event makes a curious claim: it describes the dam’s functions as hydropower, flood control and – instead of facilitating navigation – “delivering water to the lower reaches to alleviate spring droughts”. This is a singular piece of official nonsense: far from helping to relieve droughts downstream, the megadam on the Yangtze is one of their major causes. Last spring, as the reservoir filled and Poyang Lake dried up, the dam’s operators had to be ordered to let out more water.

(October 20, 2011) China’s Three Gorges reservoir is approaching its full capacity of 175m. As the water level rises, so do the risks.

Probe International

Photo taken on Oct. 18, 2011 of Three Gorges Dam (Xinhua/Zhang Xiaofeng)

China’s Three Gorges reservoir is within one metre of its normal pool level of 175m. On October 20 the reservoir reached 174.28m above sea level in this year’s attempt to bring the reservoir to its full capacity. China Three Gorges Corp., which operates the dam, said it aims to reach 175m (its normal pool level or NPL) by early November.

Probe International, a Canadian environmental organization, monitors the Three Gorges reservoir levels because a rising reservoir level can cause flooding upstream of the dam while causing drought downstream.  Also, a rising reservoir can induce landslides and a falling reservoir can induce earthquakes, putting the public at risk.

A photo from Oct. 18, 2011 of the water level in Yichang, Hubei (Xinhua/Zhang Xiaofeng)

Landslides around the Three Gorges reservoir have killed dozens in the years since the dam was built, and raising the level to 175m could increase the threat as water permeates a wider area.

Seismologists have also discovered that the biggest risk of reservoir-induced seismicity is when a dam goes into drawdown after having reached its full capacity.

This past spring, the impoundment of water in the Three Gorges reservoir also contributed to the severe drought that occurred in the lower reaches of the Yangtze, impeding navigation and threatening fishing and farming. Eventually, Chinese authorities ordered Three Gorges operators to release water, foregoing power production, in order to ease the downstream drought.

A cargo ship in Xiling Gorge, in the upper reaches of the reservoir. Oct. 18, 2011 (Xinhua/Zhang Xiaofeng)

Hydropower output is subject to the vagaries of river flow and the latest reports for China indicate that flows are down in the country’s major rivers, making competition for diminished flows even more intense.

As China’s largest dam, Three Gorges’ operations will be under intense scrutiny over the coming months. Latest readings indicate that the inflow of water is slowing as the reservoir reaches its normal pool level of 175, while the outflow has eased upwards.

Stay tuned with Probe International while we track the Yangtze River’s flow through the reservoir here.

1 reply »

  1. Check with your reservoir-effects experts. You should be told that landslide threats specifically related to changes in reservoir levels (and not to concurrent rains) are related to rapid declines in reservoir levels not to rising in reservoir levels. If the reservoir is kept at a higher level for several months the watertable in the adjacent slope adjusts to the high level, if the reservoir level drops quickly (worst case is a breach in the dam that holds back the water) the pore pressures in the saturated zone below the side slope are higher than atmospheric pressure on the exposed surface of the sideslope above the new low waterlevel. This excess pore pressure reduces the frictrional forces holding the slope in place and ;landslides can occur.

    Hugh Whiteley P. Eng.

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