The Three Gorges Dam in China is the largest hydroelectric project ever constructed in history, as noted by CNN in a 2020 article. To date, this record remains unbroken.
The entire project cost 200 billion yuan (28.6 billion USD), took nearly two decades to build, and required the relocation of over 1 million people along the Yangtze River. Completed in 2006, the Three Gorges Dam boasts impressive dimensions: it stands 181 meters tall and spans 2,335 meters across the Yangtze River.
When construction began in 1994, this dam was designed not only to generate electricity to spur economic growth in China but also to tame the longest river in Asia (the Yangtze River, known as Chang Jiang – the third longest river in the world) to protect millions from devastating floods.
Blocking the flow of the third longest river in the world at its steepest and most dangerous points marked a significant advancement in the construction of China’s Three Gorges Dam. This super dam is comparable to the efforts of the Pharaohs who built the pyramids of Egypt, as commented by the Washington Post.
An aerial photo taken on July 27, 2020, shows floodwaters being released from the Three Gorges Dam in Hubei Province, central China. (Image: Wang Gang/Xinhua via Getty Images).
Chinese media reports that the Three Gorges Dam is also a “massive electricity producer” with astonishing power generation capacity. The hydroelectric plant at the Three Gorges Dam (completed in 2012) has a total installed capacity of 22,500 megawatts, more than three times the capacity of the Grand Coulee Dam, the largest dam in the U.S., according to CNN.
The ECNS (Chinese news agency) stated that over the past 20 years, the Three Gorges Dam has contributed more than 22 trillion yuan (over 3 trillion USD) to China’s economic development.
In the years 2018, 2020, and 2021, the annual electricity output of the hydroelectric plant at the Three Gorges Dam exceeded 100 billion kilowatt-hours (kWh). In 2020 alone, the Three Gorges Dam generated a total of 111.8 billion kWh of clean electricity, setting a world record.
“Although the Three Gorges project brings enormous comprehensive benefits, there are still urgent issues that need to be addressed,” the Chinese State Council stated in a declaration.
The Challenges of the Three Gorges Dam
Not only has the dam affected the livelihoods of millions of people (due to forced relocation), but the Three Gorges Dam has also had serious geological impacts.
The immense weight of the water behind the Three Gorges Dam has started to erode the banks of the Yangtze River in many areas, and the frequent fluctuations in water levels have resulted in a series of landslides, reported Xinhua.
NASA noted that the most surprising fact is that this dam actually has the ability to slow the rotation of the Earth due to the colossal mass of the reservoir.
Furthermore, the deepest concern at the Three Gorges Dam is sedimentation. By blocking the flow of the Yangtze River, the dam has trapped a large volume of sediment, not only reducing the flood control capacity by filling up the reservoir but also causing significant erosion downstream.
Chinese media reported that 18 years after the construction of the Three Gorges Dam (2006-2024), the dam has accumulated 1.8 billion tons of sediment, enough to form a small mountain.
A 2024 study published on ResearchGate (Europe), conducted by Associate Professor Bas Van Maren (Delft University of Technology, Netherlands) and Professor Shilun Yang (East China Normal University, China), indicated:
“The sediment load of the Yangtze River (China) has been decreasing over the past two decades due to the influence of the Three Gorges Dam.”
The Yangtze River has a watershed area of 1.8×106 km2 and a flow rate of approximately 30×103 m3/second. The long-term average sediment load (from 1950 to 2000) at Yichang (downstream of the Three Gorges Dam today) was 501 million tons/year.”
The inflow rate into the massive Three Gorges Dam was 75,000 cubic meters per second in 2020. (Image: Xinhua/PA).
After the Three Gorges Dam became operational, the sediment load of the Yangtze River has decreased significantly. During the initial phase of dam implementation (2003-2005), 64% of the sediments entering the Three Gorges Reservoir were retained. In subsequent years, over 80% of the sediments entering the reservoir continued to be trapped.
Moreover, the size of sediment particles has also changed before and after the Three Gorges Dam became operational. Before the dam was built, the average annual particle size of the suspended load of the Yangtze River was approximately 10 μm (micrometers). After becoming operational, this number decreased to an average of 4.4 μm.
What does this figure indicate? It means that after the dam became operational, the Yangtze River only released very fine clay and silt from the Three Gorges Dam. Coarser sediments (such as silt and sand) are only released when large flood discharges are made.
The Catastrophic Consequences of Sediment Accumulation
It is important to note that the Three Gorges Dam is built on the Yangtze River. Being a dam, it blocks the river flow to a certain extent. The accumulation of sediment caused by the large volume of water will impact the nearby Chongqing area if it continues for an extended period. Once hidden dangers arise, the consequences could be devastating.
Professor and renowned hydraulic engineer Huang Wanli predicted long ago that the Three Gorges Dam would cause the ports of Chongqing to be clogged with sediment and gravel within a decade.
Professor and hydraulic engineer Huang Wanli. (Image: Huang Wanli).
Washington Post quoted several Chinese hydrologists who argued that the heavy sediment load of the Yangtze River and its shifting gravel layers would hinder the very turbines of the Three Gorges Dam (affecting power generation efficiency), fill the bottom of the reservoir (impacting the ecological environment), and lead to even worse flooding (affecting people and the economy).
“The engineers of the project overlooked the thick layers of gravel and sand at the riverbed that move slowly downstream over time. When combined with the 540 million tons of suspended mud in the water each year, the gravel and sand will accumulate at the bottom of the reservoir, undermining all dredging efforts. The sedimentation of hundreds of millions of tons each year will certainly block the Chongqing port, inundate upstream land, and threaten to cause significant human casualties.” – Professor Huang Wanli warned.
Professor Huang Wanli’s warnings nearly 30 years ago have partially come true. According to statistics after 18 years of operation of the Three Gorges Dam, the dam has accumulated 1.8 billion tons of sediment. Notably, this process is still increasing at a rate of 100 million tons of sediment accumulating each year.
Why can the sedimentation process cause flooding? This is because as sediment increases, the useful capacity of the reservoir decreases. This will diminish the water regulation capability of the reservoir, affecting the flood control processes. As a result, this will increase the risk of flooding in the central and downstream areas of the Yangtze River, which is a densely populated and economically developed region.
This may be a major challenge for China. Addressing the sedimentation issue is not only essential for maintaining the normal operation of the Three Gorges Reservoir, but more importantly, it is crucial for protecting the ecological environment of the Yangtze River, ensuring sustainable use of water resources, and safeguarding human safety.
