The Three Gorges Dam, the world’s largest hydropower project, has contained the first large flood of this year with a capacity of 40,000 cubic meters per second, according to the operator on Wednesday.
The flood reached the Three Gorges Reservoir in Yichang, Central China’s Hubei Province at 8 pm, Monday. Due to the heavy rainfall recorded between July 9-11 in the upper stream and tributaries of the Yangtze River, the reservoir has seen a daily rise of the inflow of up to 10,000 cubic meters per second.
Recently, record rains have inundated central China with floods striking an underground subway system, damaging dams and riverbanks, and causing landslides and building collapses.
Fears re-emerge periodically over the structural integrity of the Three Gorges Dam on the upper Yangtze, the world’s largest hydroelectric dam, built in an area criss-crossed by geological faultlines.
In 2020, the Yangtze River encountered several rounds of heavy floods. Water levels reached historic highs in 53 rivers during China’s summer last year, according to China’s ministry of water resources, as authorities warned the Three Gorges Dam is facing the largest flood peak since it began operating in 2003.
What is Three Gorges Dam?
The Three Gorges Dam is a hydroelectric gravity dam that spans the Yangtze River by the town of Sandouping, in Yiling District, Yichang, Hubei province, central China, downstream of the Three Gorges. The Three Gorges Dam has been the world’s largest power station in terms of installed capacity (22,500 MW) since 2012. The dam generates an average 95±20 TWh of electricity per year, depending on annual amount of precipitation in the river basin. After the extensive monsoon rainfalls of 2020, the dam’s annual production nearly reached 112 TWh, breaking the previous world record of ~103 TWh set by Itaipu Dam in 2016.
The dam body was completed in 2006. The power plant of the dam project was completed and fully functional as of July 4, 2012, when the last of the main water turbines in the underground plant began production. Each main water turbine has a capacity of 700 MW. Coupling the dam’s 32 main turbines with two smaller generators (50 MW each) to power the plant itself, the total electric generating capacity of the dam is 22,500 MW. The last major component of the project, the ship lift, was completed in December 2015.
Massive earthquake slashes 30% off power from China’s No.2 and No.3 hydro dams
A reported 30% plummet in electricity output at two sister dams to China’s Three Gorges complex– at 22.6GW, the world’s biggest power plant of any kind – has deepened fears that earthquakes caused by dam building and operation will continue to cripple electricity in one of the world’s most tremor-prone regions.
Power output during 2021’s second three months was down 31.8% and 27.3% respectively at the colossal Xiluoduand Xiangjiaba dams on the upper Yangtze, their operator China Yangtze Power Company told London investors last week.
Operating for only seven years, the two plants are upstream sisters of the Three Gorges complex.
On 21 May this year, 270 miles upstream and south-west of the two stricken hydro plants, the city of Dali close to Tibet suffered a 6.1 magnitude earthquake. Geologists put its epicentre at up to 10 kilometres deep. Deaths from the quake were officially registered by Chinese authorities at three, but with 12,882 properties damaged.
During its filling in 2013, the Xiluodu reservoir suffered at least one catastrophic landslide, as a result of a 6.5 magnitude quake centred 40 kilometres away. The quake reportedly killed 600 and displaced 300,000 more.
Both hydro plants lie 50 miles apart, on the upper Yangtze, Asia’s longest river at 3,915 miles or 6,300 kilometres. Known in its upper reaches as the Jinsha, the river rises in Yunnan province in China’s far south west.
Mountainous Yunnan is riddled with deep geological flaws, in the shadow of the Himalayas and Tibet where the Eurasian and Indian tectonic plates collide.
The province’s decade-long boom in building dams and filling their mega-reservoirs has caused fears among Chinese geologists that reservoir construction may actively cause quakes.
“..when water flows quickly into resulting reservoirs, it can change the stress on faults deep underground, either from the sheer weight of the water, or when water infiltrates the rocks through cracks and pores. These events might accelerate a fault’s natural ‘seismic clock’, hastening an earthquake that is already building, or increase the chance of one occurring at all”.
At least three quakes in the region over eighteen months included one in April 2014 at Yongshan, only seven kilometres from the Xiluodu reservoir. All the quakes had coincided with reservoir filling, according to reports.
(Source: The Energyst)
The fatal design flaw of the Three Gorges Dam
Huang Wanli (1911-2001), a renowned Chinese hydraulic engineer known for his strong opposition to the Three Gorges Dam project, pointed out that the biggest design flaw of the dam is its inability in flood control.