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Three Gorges Dam: The Largest Dam in the World

When we talk about megaprojects, there is one colossus that really stands out. A project both vastly ambitious and hugely controversial. Almost 90 years from its inception to its opening in 2003, it is now the biggest hydroelectric dam anywhere in the world. A true beast, which has shattered countless records for size, weight and power generated. With enough concrete to build eight Hoover Dams and the steel equivalent of sixty-three Eiffel Towers, there’s never been anything quite like the Three Gorges Dam.   

Stretching across the Yangtze River in China’s Hubei district, the Three Gorges Dam has become a symbol of Chinese progress. This staggering project raised the bar of human achievement but came at an eye-watering cost, both in terms of monetary value, but also to those living nearby. This dam was always going to be a balancing act. From its early designs, it was clear that this was a project that could bring huge benefits to a country eager to cement its place as a world leader but also had the potential to cause enormous human and ecological suffering.   

What we see today is truly impressive. At 175 metres(574 ft) in height, 181 metres (593 ft) in width at its base and 1.5 miles (2.4km) in length it is by far the largest dam in the world, capable of producing 22,500 megawatts of electricity. Its reservoir can hold an astonishing 9.43 cubic miles (39.3 cubic km) of water, which would weigh around 43 billion tonnes. This is a man-made concentration of water so large, that it has slowed the rotation of the Earth. NASA has estimated that because of the dam, Earth’s days are now 0.06 microseconds longer (a microsecond being a millionth of a second), while the poles have shifted by about 2cm.  

An Old Idea

While the Three Gorges Dam is a wonder of modern technology and engineering, the idea originated 75 years before construction began in 1994. Sun Yat-Sen, a former president of the Republic of China, first floated the idea of a dam on the Yangtze river in 1919, in order to generate electricity but also an attempt to reduce the impact of the river’s devastating floods. 

At 3915 miles (6300km) the Yangtze is the third-longest river in the world and has an estimated 400 million people living beside it, or close by – that’s over 70 million more than live in the entire United States. When the Yangtze floods it can cause devastation. Sadly this has always been an annual occurrence, but the impact varies greatly from year to year. The worst flood the Yangtze has ever seen came in 1935, which resulted in the deaths of 145,000 people and remains the 5th worst flood in history. But to give you a good idea of just how bad this situation can be in China, the top five worst floods ever have all occurred in the country. The worst of which in 1931 killed between 1 million and 4 million people. 

In 1932 preliminary work began on the dam by the Nationalist government, but came to a grinding halt in 1939 with the Japanese invasion of China. As invasion turned to occupation, the Japanese took up the project themselves, eager for a showcase venture that would celebrate their imminent victory over the Chinese. But as things began to unravel for the Imperial Japanese forces in China, and around Asia, the project was once again abandoned. 

Despite the ongoing fighting, and perhaps with one eye on the future, the Chinese government recruited an American by the name of John L Savage, head design engineer of the United States Bureau of Reclamation to survey the area and put forth a proposal. 

His work was greeted with enthusiasm and 54 Chinese engineers were packed off to the United Stated for training, while surveys and economic studies began to inspect the feasibility of the project. But once again, war broke out. 

The Chinese civil war, which had seen fighting intermittently since 1927, reared its head again in 1947, effectively halting any work on the dam project. What emerged in 1949 was a very different China. The victorious communist rebels led by Mao Zedong quickly took control of the country. Mao himself was a supporter of the project but opted first to draw up plans for the Gezhouba dam in Yichang, a project which was eventually shelved as the disastrous effects of the Great Leap Forward took effect.

A catastrophic flood of the Yangtze in 1954 reignited plans after Mao penned his famous poem, Swimming, in which he speaks lovingly of his desire for a dam. In 1958 Chinese authorities announced the Hundred Flowers Campaign in which people were encouraged to voice their opinions and thoughts about the Communist regime. Numerous engineers spoke out against tentative plans for a dam on the Yangtze and quickly found themselves in jail as a consequence. The entire campaign came to an end with a brutal crackdown on dissent. The tiny window of free speech had slammed shut, and names had been taken. 

It wasn’t until after the death of Mao Zedong in 1976 that plans for the dam began to re-emerge, but it remained highly controversial in terms of its social impact, impacts we’ll be getting to shortly. In 1992 a vote was put forward at the Chinese congress. Now bear in mind that this congress is very different from what we see in other countries. China has effectively been run by a politburo, a group of senior leaders, or an outright leader for as long as could be remembered.  While votes are indeed cast in congress, the process is very much seen as symbolic. In its entire history, the Chinese congress has never voted down a proposal put forward by the politburo. But this was as close as it has ever come. Of the 3000 delegates in congress that day, only 67.75% voted yes.

The Good and the Bad

So what exactly were the doubts? They weren’t so much about the dam itself, but the consequences to the area. The design called for the flooding of three gorges, Qutang, Wu Xia, and Xiling, areas known throughout China for their outstanding beauty. This has always been an area rich in biodiversity, home to some 6,388 different plant species, of which 57% are considered endangered. The proposed 410 mile-long reservoir would flood 244 square miles of land, displacing vast amounts of people and submerging countless cities, towns and villages. Compensation packages had been put in place for those displaced, including money and new homes away from the flooded area, but many remained fearful. Archaeological sites would also disappear beneath the water, including important sites of the Ba people who lived in the area over 4000 years ago.    

On the other hand, proponents of the project argued that the dam would significantly reduce China’s reliance on coal power stations, while also opening up the Yangtze to trade like never before. With a higher water level, they estimated that barge capacity could be raised five or six-fold. Then there were the claims that the dam would be able to regulate water levels meaning terrible flooding would now be a thing of the past.

Work Begins                     

The first phase began in 1993 with the excavation of a side-channel where water could be diverted to from the river during the main construction process. Construction finally began on the dam itself on December 14th 1994 and I’m sure that you won’t be surprised to hear that it was the largest construction project in China at that time. 

One of the biggest obstacles to engineers was the need to keep the river open during construction, for both water flow and river traffic. To do this they began the construction of large concrete structures known as cofferdams which essentially blocked off sections of water to allow construction. These were built on several tons of earth placed onto the dry river bed. Once these were finished they would act as a shield in front of the actual dam built behind them. 

The river was officially ‘dammed’ in November 1997, causing water levels to rise as much as 10 metres and ending the first phase of construction.   

The second phase began shortly after with the addition of the concrete. That sounds like a quick process but what began from the left-hand bank working slowly right, took a total of 4 years. Once the concrete was in place the first turbines and generators were slowly added. The cofferdams were then destroyed with explosives, allowing the water to finally reach their intended destination, the turbines. 

Unsurprisingly, the decision was taken to bring the generators online in stages, that way the dam could begin generating electricity without being complete. Generator No 2, on the north side, holds the distinction of becoming the first active generator on 10th July 2003. The entire north side became operational on 7th September 2005 but ran at reduced power until 18th October 2006, when after the water level in the reservoir reached 156 metres, it finally reached 9,800 MW. 

On the south side, generator No. 22 became operational on 11th June 2007, with successive generators starting up over the following years. 18th December 2007, was an important date for the Three Gorges Dam as it finally reached 14.1 GW, surpassing the Itaipu Dam on the Brazilian/Paraguay border to become the largest hydro dam in the world in terms of output. The final main generator, No. 27, became operational on 23rd May 2012.   

Three Gorges Dam - China 2009
Three Gorges Dam – China 2009 by Rehman is licensed under CC-BY

In total there are thirty-three enormous turbines, each capable of producing 700MW of electricity, along with thirty-four generators weighing 6000 tons each. When the dam is running at full capacity it is producing just over four times the energy of the most powerful nuclear power station in the world, and could provide the daily electricity requirement for around 20 million people in the UK. Water is directed into the dam and down concrete tubes to the turbines, enabling them to spin and activating the generators – and so producing electricity. Of these generators, 14 were installed on the north side of the dam, 12 on the south side and the remaining 6 in the mountains south of the dam.

Perhaps the biggest worry about the dam isn’t what you can see, but what you can’t. The foundations of the Three Gorges Dam is by far the most vital aspect. Any failure here could lead to an unimaginable disaster. To try and alleviate some of the pressure on the foundations, as well as helping to regulate water levels, a 483-metre spillway was installed in the centre of the dam, which can be opened and closed allowing more or less water to travel through. This includes 22 sluice gates, each 8 metres wide which fire water through at an astonishing rate.      

The dam receives over 150 freight ships per day, making it one of the biggest locks in the world. Ships are enclosed within the locks then move up or down, depending on which way they are travelling, a process that takes a total of 5 hours. However, for passenger ships, this time is greatly reduced by using a different method, with a ship lift transporting boats up or down in just forty minutes. This is done by using a helical gear system, by which counterweights within the concrete walls are used to elevate the ships.    

Controversy

This has been a project with plenty of controversy from the very start, and this has continued. Shortly after the filling of the reservoir 80 hairline cracks appeared on the dam’s structure, despite all 163,000 concrete units passing quality control tests. The Chinese government was, of course, quick to dismiss these cracks, but doubts certainly remain. 

Another attack levelled at the dam is that it’s not actually doing what was promised. Remember at the start I mentioned those catastrophic floods? Well, though nothing that bad has happened, many have pointed out that the last decade has seen enormous flooding in the area. It’s likely that there are other causes of this, such as climate change, but considering the project was heavily sold on this aspect, many are understandably questioning the dam’s role. Whatsmore, the percentage of China’s total electricity gained from the dam is also considerably less than first thought. In 1993 it was believed that the dam would eventually be able to generate about 10% of China’s electrical needs, but with soaring use and an ever-growing population, that figure is now just 1.25% of Chinese power supply. 

There has also been an increase in mudslides in the area. In the first four months of 2010 alone, there were no fewer than 97 serious incidents caused by erosion in the reservoir. The Three Gorges Dam was always going to be a balance between the positive and negative outcomes. Apart from human displacement, the most significant impact has been on the environment. From the very beginning, environmentalists warned that the dam would have a serious impact on nutrients downstream, as well as sediment flow. This is likely to have enormous ramifications on eco-systems in the Yangtze, neighbouring rivers, as well as the seacoast areas.    

A report in 2006 found that ratios of silicon to nitrogen in brackish coastal waters fell from 1.5 in 1998 to 0.4 in 2004, a change that could cause significant damage to marine life in coastal areas, leading to the further depletion of fish numbers. While sediment loading, which measures solid matter carried by a river, was found in places to be half of the pre-dam levels, which is likely to lead to increased erosion in tidal wetlands, risking further landslides.    

Lastly, rumblings of corruption have gone on as long as the project has. Though of course, the Chinese government is tight-lipped about this sort of thing, rumours have long circulated. Allegedly, funds for 13,000 farmers in the Gaoyang area disappeared after being sent to the local government. 

Challenges

One problem that you might not have considered about this dam is the incredible amount of rubbish drifting naturally down the river. In 2006 it was estimated that the dam had already blocked ten million tons of rubbish that would otherwise have flowed out to sea. Now you don’t need me to tell you that all of that is going to build up and quickly get into the turbines. Once this happens, at best some of the turbines stop working, at worst it could cause a pressure build-up within the dam that if left could eventually cause huge structural damage. But they have come up with a rather ingenious solution for this. They call it the lapping tongue. A rolling track, a little like the mechanical walkways that you find in airports, attached to a garbage boat, quite literally laps up the rubbish. This device that can consume 300 cubic metres (360 cubic feet) of rubbish per hour. Where it all goes after that, well, we’re not entirely sure. But certainly far away from the dam. 

Over 5 million tons of silt and sediment become trapped at the bottom of the reservoir each year. Such a build-up can eventually have an impact on wildlife, and even mechanical systems, such as piping. With such a huge build-up, the dam needs its own system to push the silt and sediment through to the other side. The sluice gates, that regulate water levels, are also used for this and are periodically opened with the help of hydraulic pistons to push the silt and sediment through the dam and into the river beyond. 

The Final Numbers

The final numbers associated with the dam can make slightly uncomfortable reading. In total, 1.2 million people were displaced by the construction, while 140 towns, 13 cities, and 1,600 settlements disappeared underwater. Though there are no definite numbers, the Chinese government has acknowledged more than 100 deaths during the construction of the dam. 

The final cost is thought to be in the region of $37 billion, though questions have been raised as to whether that could, in fact, be even higher. However, that number doesn’t quite seem so high by the fact that by 2013 the dam had effectively paid for itself through energy output.   

There are few projects that can compare to the financial cost of the Three Gorges Dam, and perhaps none that has had the same humanitarian impact. Most likely we won’t know for many years whether it was all worth it. Will it be remembered as a magnificent human achievement that brought clean energy to China or a bloated ecological disaster that caused great hardship to millions? We’ll have to wait and see.     

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