The change caused by the dam is relatively insignificant in the larger scheme of things
The Three Gorges Dam, built across the Yangtze River in Hubei province, was first proposed in 1919 by Sun Yat-sen, the provisional first president of the Republic of China, as a measure to control the Yangtze River's flooding and to symbolise China's might. While it took decades to construct the dam, many media reports have claimed that it has an effect on the Earth's rotation.
Is it really altering the Earth's rotation? Reports indicate that the dam holds water at a level 175 meters above sea level, with a weight exceeding 39 trillion kilograms. This massive weight affects the Earth's rotation due to the moment of inertia.
In simple terms, the farther a mass is from its axis, the higher its moment of inertia, which in turn slows the rotational speed.
What is 'moment of inertia'? It is "a quantity expressing a body's tendency to resist angular acceleration, which is the sum of the products of the mass of each particle in the body with the square of its distance from the axis of rotation."
Medium reported that the huge mass of the water above sea level does increase the moment of inertia of our Earth but the change in its rotation is as little as 0.06 microseconds. That is to say, we have days that are only 0.06 microseconds longer now.
The dam had some positive effects, such as controlling flooding and generating massive amounts of power. However, 1.2 million people were forced to relocate for its construction. Erosion of the reservoir has impacted thousands of insect and fish species living in its waters. Additionally, the cost of building the dam is estimated to be a staggering $25 billion, with some estimates reaching as high as $37 billion.
To conclude, NASA scientists have noted that Earth's rotation occasionally fluctuates due to events like natural disasters and the influence of the moon. Therefore, the change caused by the dam is relatively insignificant in the larger scheme of things. However, we cannot overlook the fact that the Three Gorges Dam is the only man-made object to date with the capacity to singularly affect Earth's rotation.