Did The Three Gorges Dam Slow Down Earth’s Rotation?

by hridika ahire

Did The Three Gorges Dam Slow Down Earth’s Rotation?

April 22, 2021

A dam can actually have an impact on the rotation of our planet. The Three Gorges Dam in China is the largest hydropower project ever built. The project cost approximately $38 billion and took nearly 12 years to build. Over the years, the dam has been subjected to a lot of criticism both from scientists and environmental activists! It is humongous and can hold 39 billion cubic metres of water, but can this dam slow down the Earth's rotation?

The Three Gorges Dam is a hydroelectric gravity dam that spans the Yangtze River by the town of Sandouping, in Yiling District, Yichang

Earth’s rotation is the spinning of the planet around its own axis. When viewed from the north pole star Polaris, Earth turns in a counter-clockwise direction. The North Pole, also known as the Geographic North Pole, is the point in the Northern Hemisphere where Earth’s rotation axis meets the surface. It is not to be confused with Earth’s Magnetic Pole.

As we have learned in school, Earth rotates once in 24 hours with respect to the Sun, whereas it rotates once every 23 hours, 56 minutes, and 4 seconds with respect to other stars. We experience day and night due to this rotation of Earth. While there are a few different factors that have slowed down Earth’s rotation, the most recent factor is the Three Gorges Dam.

The Origin Of The Three Gorges Dam

The dam was originally envisioned in 1919 by Sun Yat-sen in The International Development of China. He wanted a dam capable of generating about 30 million horsepower that could be built downstream of the Three Gorges, which are three adjacent gorges that run along the middle reach of River Yangtze. The preliminary work, i.e. the planning of the dam, was started by the Nationalist Government, which was led by Chiang Kai-shek.

In 1939, the Japanese military forces conquered Yichang, and as a way of showing dominance over the Chinese, they commissioned and completed the plan named Omani. The United States Bureau of Reclamation’s design engineer, John l. Savage surveyed the area and drew a proposal for the ‘Yangtze River Project” in 1944. According to John’s plan, the dam is supposed to use a unique method of moving ships. The ships will enter locks located in the lower and upper ends of the dam, and the cranes move the ships from one lock to the next.

The original idea of the damn was envisioned in 1919 and it was built as "the project Yangtze" in 1944.

The Construction

After some impediments, the construction of the dam started on December 14, 1994. The dam was supposed to be completed and fully operational in 2009, but due to some additional projects such as the underground power plant and six additional generators, the construction delayed till May 2012.

Finally,  the Three Gorges dam, spread across the Yangtze River in Hubei province, China, was completed in 2015. It became the largest hydroelectric power station in the world and had a total capacity of 22,500MW when it was completed. The maximum limit of the dam is 175 meters (574ft) over sea level, the reservoir created by the dam measures 660 kilometers in length and 1.12 kilometers in width on average. The total surface area of the reservoir made is 1,045 square kilometers, and it floods a total area of 632 square kilometers of land. This reservoir contains about 9.43 cubic miles of water, and the water weighs more than 39 trillion kilograms. After the construction of the Three Gorges Dam, it overtook the Itaipu hydroelectric power plant in Brazil and Paraguay becoming the world’s largest hydroelectric facility.

bch TGDconstruction
The construction of the Three Gorges Dam started on December 1994 and it became fully operational in 2009.

Inertia Affected Due To The Massive Dam

When such a big dam is constructed, it affects the rotation of Earth because of a phenomenon called the moment of inertia. The moment of inertia is the tendency of a body to rotate or the tendency of a rotating body to keep on rotating. The moment of inertia of an object of a given axis describes how difficult it is to change the angular motion about that axis. It means that the longer the distance of a mass to its axis of rotation, the slower it will spin. While you may not notice it, but we see examples of it in our day-to-day life.

You may have noticed that when a figure skater attempts to spin faster, he/she will draw their arms close to their bodies, and that reduces their moment of inertia. Similarly, when a diver wants to somersault faster, they will bring their body into a tucked fetal position.

Yes. The Dam Changed Earth's Rotation

When the dam closes its doors to fill the reservoir, it accumulates 38 trillion kg of water. While this is marginal compared to Earth’s weight, it does affect Earth’s rotation. It increases Earth’s moment of inertia and thus effectively slows down its rotation. NASA scientists have acknowledged this slow down of Earth’s rotation. They even calculated that the shift of such a mass would increase the lengths of days by only 0.06 microseconds.

A minuscule change but important in our calculation of time. The shift in the rotation makes Earth slightly round in the middle and flat on the top. This can even shift the position of the North and South Poles by 2 centimeters. While a lot of factors slow down Earth’s rotations, they usually are the smallest shifts, but collectively, accumulated over a period of time can cause bigger problems.



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